Cisco IOS Switch RTR Security Technical Implementation Guide
| Version 1 Release 1 |
| 2020-05-08 |
| U_Cisco_IOS_Switch_RTR_STIG_V1R1_Manual-xccdf.xml |
| This Security Technical Implementation Guide is published as a tool to improve the security of Department of Defense (DoD) information systems. The requirements are derived from the National Institute of Standards and Technology (NIST) 800-53 and related documents. Comments or proposed revisions to this document should be sent via email to the following address: disa.stig_spt@mail.mil. |
Vulnerabilities (49)
The Cisco switch must be configured to enforce approved authorizations for controlling the flow of information within the network based on organization-defined information flow control policies.
Discussion
Information flow control regulates where information is allowed to travel within a network and between interconnected networks. The flow of all network traffic must be monitored and controlled so it does not introduce any unacceptable risk to the network infrastructure or data. Information flow control policies and enforcement mechanisms are commonly employed by organizations to control the flow of information between designated sources and destinations (e.g., networks, individuals, and devices) within information systems. Enforcement occurs, for example, in boundary protection devices (e.g., gateways, switches, guards, encrypted tunnels, and firewalls) that employ rule sets or establish configuration settings that restrict information system services, provide a packet-filtering capability based on header information, or provide a message-filtering capability based on message content (e.g., implementing key word searches or using document characteristics).
Fix Text
Configure ACLs to allow or deny traffic for specific source and destination addresses as well as ports and protocols between various subnets as required. The commands below were used to create the configuration as shown in the check content: SW1(config)#ip access-list extended FILTER_SERVER_TRAFFIC SW1(config-ext-nacl)#permit tcp any 10.1.12.0 0.0.0.255 eq 515 631 9100 SW1(config-ext-nacl)#permit tcp any 10.1.13.0 0.0.0.255 eq 1433 1434 4022 SW1(config-ext-nacl)#permit icmp any any SW1(config-ext-nacl)#permit ospf any any SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#interface g0/1 SW1(config-if)#ip access-group FILTER_SERVER_TRAFFIC in SW1(config-if)#end Alternate: Inter-VLAN routing SW1(config)#ip access-list extended FILTER_PRINTER_VLAN SW1(config-ext-nacl)#permit tcp any any eq lpd 631 9100 SW1(config-ext-nacl)#permit icmp any any SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#ip access-list extended FILTER_SQL_VLAN SW1(config-ext-nacl)#permit tcp any any eq 1433 1434 4022 SW1(config-ext-nacl)#permit icmp any any SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#interface vlan 12 SW1(config-if)#ip access-group FILTER_PRINTER_VLAN out SW1(config-if)#exit SW1(config)#interface vlan 13 SW1(config-if)#ip access-group FILTER_SQL_VLAN out SW1(config-if)#end
Check Content
Review the switch configuration to verify that ACLs are configured to allow or deny traffic for specific source and destination addresses as well as ports and protocols. For example, the configuration below will allow only printer traffic into subnet 10.1.12.0/24 and SQL traffic into subnet 10.1.13.0/24. ICMP is allowed for troubleshooting and OSPF is the routing protocol used within the network. interface GigabitEthernet0/1 no switchport ip address 10.2.1.1 255.255.255.252 ip access-group FILTER_SERVER_TRAFFIC in … … … ip access-list extended FILTER_SERVER_TRAFFIC permit tcp any 10.1.12.0 0.0.0.255 eq lpd 631 9100 permit tcp any 10.1.13.0 0.0.0.255 eq 1433 1434 4022 permit icmp any any permit ospf any any deny ip any any Alternate: Inter-VLAN routing interface Vlan12 ip address 10.1.12.1 255.255.255.0 ip access-group FILTER_PRINTER_VLAN out ! interface Vlan13 ip address 10.1.13.1 255.255.255.0 ip access-group FILTER_SQL_VLAN out … … … ip access-list extended FILTER_PRINTER_VLAN permit tcp any any eq lpd 631 9100 permit icmp any any deny ip any any ip access-list extended FILTER_SQL_VLAN permit tcp any any eq 1433 1434 4022 permit icmp any any deny ip any any If the switch is not configured to enforce approved authorizations for controlling the flow of information within the network based on organization-defined information flow control policies, this is a finding.
The Cisco switch must be configured to implement message authentication for all control plane protocols.
Discussion
A rogue switch could send a fictitious routing update to convince a site's perimeter switch to send traffic to an incorrect or even a rogue destination. This diverted traffic could be analyzed to learn confidential information about the site's network or used to disrupt the network's ability to communicate with other networks. This is known as a "traffic attraction attack" and is prevented by configuring neighbor switch authentication for routing updates. This requirement applies to all IPv4 and IPv6 protocols that are used to exchange routing or packet forwarding information; this includes all Interior Gateway Protocols (such as OSPF, EIGRP, and IS-IS) and Exterior Gateway Protocols (such as BGP), MPLS-related protocols (such as LDP), and multicast-related protocols.
Fix Text
Configure authentication to be enabled for every protocol that affects the routing or forwarding tables. The example configuration commands below enables OSPF and EIGRP authentication. EIGRP example: SW1(config)#key chain EIGRP_KEY SW1(config-keychain)#key 1 SW1(config-keychain-key)#key-string xxxxx SW1(config-keychain-key)#exit SW1(config-keychain)#exit SW1(config)#int g0/0 SW1(config-if)#ip authentication mode eigrp 1 md5 SW1(config-if)#ip authentication key-chain eigrp 1 EIGRP_KEY SW1(config-if)#end OSPF example: SW1(config)#int g0/0 SW1(config-if)#ip ospf authentication-key xxxxx SW1(config-if)#end
Check Content
Review the switch configuration. Verify that authentication is enabled for all routing protocols. The configuration examples below depict OSPF and EIGRP authentication. EIGRP example: key chain EIGRP_KEY key 1 key-string xxxxxxx … … … interface GigabitEthernet0/0 no switchport ip address x.x.x.x 255.255.255.0 ip authentication mode eigrp 1 md5 ip authentication key-chain eigrp 1 EIGRP_KEY OSPF example: interface GigabitEthernet0/0 no switchport ip address x.x.x.x 255.255.255.0 ip ospf authentication-key xxxxx If authentication is not enabled on all routing protocols, this is a finding.
The Cisco switch must be configured to use keys with a duration not exceeding 180 days for authenticating routing protocol messages.
Discussion
If the keys used for routing protocol authentication are guessed, the malicious user could create havoc within the network by advertising incorrect routes and redirecting traffic. Some routing protocols allow the use of key chains for authentication. A key chain is a set of keys that is used in succession, with each having a lifetime of no more than 180 days. Changing the keys frequently reduces the risk of them eventually being guessed. Keys cannot be used during time periods for which they are not activated. If a time period occurs during which no key is activated, neighbor authentication cannot occur, and therefore routing updates will fail. Therefore, ensure that for a given key chain, key activation times overlap to avoid any period of time during which no key is activated.
Fix Text
Configure each key used for routing protocol authentication to have a lifetime of no more than 180 days as shown in the example below: SW1(config)#key chain OSPF_KEY_CHAIN SW1(config-keychain)#key 1 SW1(config-keychain-key)#key-string xxxxxx SW1(config-keychain-key)#send-lifetime 00:00:00 Jan 1 2018 23:59:59 Mar 31 2018 SW1(config-keychain-key)#accept-lifetime 00:00:00 Jan 1 2018 01:05:00 Apr 1 2018 SW1(config-keychain-key)#exit SW1(config-keychain)#key 2 SW1(config-keychain-key)#key-string yyyyyyy SW1(config-keychain-key)#send-lifetime 00:00:00 Apr 1 2018 23:59:59 Jun 30 2018 SW1(config-keychain-key)#accept-lifetime 23:55:00 Mar 31 2018 01:05:00 Jul 1 2018 SW1(config-keychain-key)#end
Check Content
Review the start times for each key within the configured key chains used for routing protocol authentication as shown in the example below: key chain OSPF_KEY_CHAIN key 1 key-string xxxxxxx send-lifetime 00:00:00 Jan 1 2018 23:59:59 Mar 31 2018 accept-lifetime 00:00:00 Jan 1 2018 01:05:00 Apr 1 2018 key 2 key-string yyyyyyy send-lifetime 00:00:00 Apr 1 2018 23:59:59 Jun 30 2018 accept-lifetime 23:55:00 Mar 31 2018 01:05:00 Jul 1 2018 Note: Key chains must be configured to authenticate routing protocol messages, as it is the only way to set an expiration. If any key has a lifetime of more than 180 days, this is a finding.
The Cisco switch must be configured to use encryption for routing protocol authentication.
Discussion
A rogue switch could send a fictitious routing update to convince a site's perimeter switch to send traffic to an incorrect or even a rogue destination. This diverted traffic could be analyzed to learn confidential information about the site's network or used to disrupt the network's ability to communicate with other networks. This is known as a "traffic attraction attack" and is prevented by configuring neighbor switch authentication for routing updates. However, using clear-text authentication provides little benefit since an attacker can intercept traffic and view the authentication key. This would allow the attacker to use the authentication key in an attack. This requirement applies to all IPv4 and IPv6 protocols that are used to exchange routing or packet forwarding information; this includes all Interior Gateway Protocols (such as OSPF, EIGRP, and IS-IS) and Exterior Gateway Protocols (such as BGP), MPLS-related protocols (such as LDP), and multicast-related protocols.
Fix Text
Configure all routing protocol authentications to encrypt the authentication key. EIGRP example: SW2(config)#int g0/1 SW2(config-if)#ip authentication mode eigrp 1 md5 SW2(config-if)#ip authentication key-chain eigrp 1 EIGRP_KEY_CHAIN OSPF example: SW1(config)#int g1/0 SW1(config-if)#ip ospf authentication message-digest SW1(config-if)#ip ospf message-digest-key 1 md5 xxxxxx RIP example: SW2(config)#int g1/0 SW2(config-if)#ip rip authentication mode md5 SW2(config-if)#ip rip authentication key-chain RIP_KEY_CHAIN
Check Content
Review the switch configuration. For every routing protocol that affects the routing or forwarding tables, verify that the switch is encrypting the authentication key as shown in the examples below: EIGRP example: interface GigabitEthernet1/0 no switchport ip address x.x.x.x 255.255.255.0 ip authentication mode eigrp 1 md5 ip authentication key-chain eigrp 1 EIGRP_KEY_CHAIN OSPF example: interface GigabitEthernet1/0 no switchport ip address x.x.x.x 255.255.255.0 ip ospf authentication message-digest ip ospf message-digest-key 1 md5 xxxxxx RIP example: interface GigabitEthernet1/0 no switchport ip rip authentication mode md5 ip rip authentication key-chain RIP_KEY_CHAIN If the routing protocol is not encrypting the authentication key, this is a finding.
The Cisco switch must be configured to authenticate all routing protocol messages using NIST-validated FIPS 198-1 message authentication code algorithm.
Discussion
A rogue switch could send a fictitious routing update to convince a site's perimeter switch to send traffic to an incorrect or even a rogue destination. This diverted traffic could be analyzed to learn confidential information about the site's network or used to disrupt the network's ability to communicate with other networks. This is known as a "traffic attraction attack" and is prevented by configuring neighbor switch authentication for routing updates. However, using clear-text authentication provides little benefit since an attacker can intercept traffic and view the authentication key. This would allow the attacker to use the authentication key in an attack. Since MD5 is vulnerable to "birthday" attacks and may be compromised, routing protocol authentication must use FIPS 140-2 validated algorithms and modules to encrypt the authentication key. This requirement applies to all IPv4 and IPv6 protocols that are used to exchange routing or packet forwarding information; this includes all Interior Gateway Protocols (such as OSPF, EIGRP, and IS-IS) and Exterior Gateway Protocols (such as BGP), MPLS-related protocols (such as LDP), and multicast-related protocols.
Fix Text
Configure routing protocol authentication to use a NIST-validated FIPS 198-1 message authentication code algorithm as shown in the example below: SW1(config)#key chain OSPF_KEY_CHAIN SW1(config-keychain)#key 1 SW1(config-keychain-key)#key-string xxxxxx SW1(config-keychain-key)#send-lifetime 00:00:00 Jan 1 2018 23:59:59 Mar 31 2018 SW1(config-keychain-key)#accept-lifetime 00:00:00 Jan 1 2018 01:05:00 Apr 1 2018 SW1(config-keychain-key)#cryptographic-algorithm hmac-sha-256 SW1(config-keychain-key)#exit SW1(config-keychain)#key 2 SW1(config-keychain-key)#key-string yyyyyyy SW1(config-keychain-key)#send-lifetime 00:00:00 Apr 1 2018 23:59:59 Jun 30 2018 SW1(config-keychain-key)#accept-lifetime 23:55:00 Mar 31 2018 01:05:00 Jul 1 2018 SW1(config-keychain-key)#cryptographic-algorithm hmac-sha-256 SW1(config-keychain-key)#end SW1(config)#interface GigabitEthernet0/2 SW1(config-if)#ip ospf authentication key-chain OSPF_KEY_CHAIN
Check Content
Review the switch configuration to verify it is using a NIST-validated FIPS 198-1 message authentication code algorithm to authenticate routing protocol messages. OSPF example: key chain OSPF_KEY_CHAIN key 1 key-string xxxxxxx send-lifetime 00:00:00 Jan 1 2018 23:59:59 Mar 31 2018 accept-lifetime 00:00:00 Jan 1 2018 01:05:00 Apr 1 2018 cryptographic-algorithm hmac-sha-256 key 2 key-string yyyyyyy send-lifetime 00:00:00 Apr 1 2018 23:59:59 Jun 30 2018 accept-lifetime 23:55:00 Mar 31 2018 01:05:00 Jul 1 2018 cryptographic-algorithm hmac-sha-256 … … … interface GigabitEthernet0/1 no switchport ip address x.x.x.x 255.255.255.0 ip ospf authentication key-chain OSPF_KEY_CHAIN If a NIST-validated FIPS 198-1 message authentication code algorithm is not being used to authenticate routing protocol messages, this is a finding.
The Cisco switch must be configured to have all inactive Layer 3 interfaces disabled.
Discussion
An inactive interface is rarely monitored or controlled and may expose a network to an undetected attack on that interface. Unauthorized personnel with access to the communication facility could gain access to a switch by connecting to a configured interface that is not in use. If an interface is no longer used, the configuration must be deleted and the interface disabled. For sub-interfaces, delete sub-interfaces that are on inactive interfaces and delete sub-interfaces that are inactive. If the sub-interface is no longer necessary for authorized communications, it must be deleted.
Fix Text
Disable all inactive interfaces as shown below: SW1(config)#interface GigabitEthernet3 SW1(config-if)#shutdown SW1(config)#interface GigabitEthernet4 SW1(config-if)#shutdown
Check Content
Review the switch configuration and verify that inactive interfaces have been disabled as shown below: interface GigabitEthernet3 no switchport shutdown ! interface GigabitEthernet4 no switchport shutdown If an interface is not being used but is configured or enabled, this is a finding.
The Cisco switch must be configured to have all non-essential capabilities disabled.
Discussion
A compromised switch introduces risk to the entire network infrastructure, as well as data resources that are accessible via the network. The perimeter defense has no oversight or control of attacks by malicious users within the network. Preventing network breaches from within is dependent on implementing a comprehensive defense-in-depth strategy, including securing each device connected to the network. This is accomplished by following and implementing all security guidance applicable for each node type. A fundamental step in securing each switch is to enable only the capabilities required for operation.
Fix Text
Disable the following services if enabled as shown in the example below: SW2(config)#no boot network SW2(config)#no ip boot server SW2(config)#no ip bootp server SW2(config)#no ip dns server SW2(config)#no ip identd SW2(config)#no ip finger SW2(config)#no ip http server SW2(config)#no ip rcmd rcp-enable SW2(config)#no ip rcmd rsh-enable SW2(config)#no service config SW2(config)#no service finger SW2(config)#no service tcp-small-servers SW2(config)#no service udp-small-servers SW2(config)#no service pad
Check Content
Review the switch configuration to verify that the switch does not have any unnecessary or non-secure services enabled. For example, the following commands should not be in the configuration: boot network ip boot server ip bootp server ip dns server ip identd ip finger ip http server ip rcmd rcp-enable ip rcmd rsh-enable service config service finger service tcp-small-servers service udp-small-servers service pad If any unnecessary services are enabled, this is a finding.
The Cisco switch must not be configured to have any feature enabled that calls home to the vendor.
Discussion
Call home services will routinely send data such as configuration and diagnostic information to the vendor for routine or emergency analysis and troubleshooting. There is a risk that transmission of sensitive data sent to unauthorized persons could result in data loss or downtime due to an attack.
Fix Text
Disable the call home feature as shown below: SW1(config)#no call-home
Check Content
Review the switch configuration to determine if the call home service is enabled as shown in the example below: call-home contact-email-addr username@example.com phone-number "+1-800-555-4567" customer-id "Customer1234" contract-id "Company1234" If the call home feature is configured to call home to the vendor, this is a finding.
The Cisco switch must not be configured to have any zero-touch deployment feature enabled when connected to an operational network.
Discussion
Network devices that are configured via a zero-touch deployment or auto-loading feature can have their startup configuration or image pushed to the device for installation via TFTP or Remote Copy (rcp). Loading an image or configuration file from the network is taking a security risk because the file could be intercepted by an attacker who could corrupt the file, resulting in a denial of service.
Fix Text
Disable configuration auto-loading if enabled using the following commands: SW1(config)#no boot network SW1(config)#no service config Disable CNS zero-touch deployment if enabled as shown in the example below: SW2(config)#no cns config initial SW2(config)#no cns exec SW2(config)#no cns image SW2(config)#no cns trusted-server config x.x.x.x SW2(config)#no cns trusted-server image x.x.x.x
Check Content
Review the device configuration to determine if auto-configuration or zero-touch deployment via Cisco Networking Services (CNS) is enabled. Auto-configuration example: version 15.0 service config … … … boot-start-marker boot network tftp://x.x.x.x/R5-config boot-end-marker CNS Zero-Touch example: cns trusted-server config x.x.x.x cns trusted-server image x.x.x.x cns config initial x.x.x.x 80 cns exec 80 cns image If a configuration auto-loading feature or zero-touch deployment feature is enabled, this is a finding. Note: Auto-configuration or zero-touch deployment features can be enabled when the switch is offline for the purpose of image loading or building out the configuration. In addition, this would not be applicable to the provisioning of virtual switches via a software-defined network (SDN) orchestration system.
The Cisco switch must be configured to protect against or limit the effects of denial-of-service (DoS) attacks by employing control plane protection.
Discussion
The Route Processor (RP) is critical to all network operations because it is the component used to build all forwarding paths for the data plane via control plane processes. It is also instrumental with ongoing network management functions that keep the switches and links available for providing network services. Any disruption to the RP or the control and management planes can result in mission-critical network outages. A DoS attack targeting the RP can result in excessive CPU and memory utilization. To maintain network stability and RP security, the switch must be able to handle specific control plane and management plane traffic that is destined to the RP. In the past, one method of filtering was to use ingress filters on forwarding interfaces to filter both forwarding path and receiving path traffic. However, this method does not scale well as the number of interfaces and the size of the ingress filters grow. Control plane policing increases the security of switches and multilayer switches by protecting the RP from unnecessary or malicious traffic. Filtering and rate limiting the traffic flow of control plane packets can be implemented to protect switches against reconnaissance and DoS attacks, allowing the control plane to maintain packet forwarding and protocol states despite an attack or heavy load on the switch or multilayer switch.
Fix Text
Configure the Cisco switch to protect against known types of DoS attacks on the route processor. Implementing a CoPP policy as shown in the example below is a best practice method: Step 1: Configure ACL specific traffic types. SW1(config)#ip access-list extended CoPP_CRITICAL SW1(config-ext-nacl)#remark our control plane adjacencies are critical SW1(config-ext-nacl)#permit ospf host x.x.x.x any SW1(config-ext-nacl)#permit ospf host x.x.x.x any SW1(config-ext-nacl)#permit pim host x.x.x.x any SW1(config-ext-nacl)#permit pim host x.x.x.x any SW1(config-ext-nacl)#permit igmp any 224.0.0.0 15.255.255.255 SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#ip access-list extended CoPP_IMPORTANT SW1(config-ext-nacl)#permit tcp host x.x.x.x eq tacacs any SW1(config-ext-nacl)#permit tcp x.x.x.x 0.0.0.255 any eq 22 SW1(config-ext-nacl)#permit udp host x.x.x.x any eq snmp SW1(config-ext-nacl)#permit udp host x.x.x.x eq ntp any SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#ip access-list extended CoPP_NORMAL SW1(config-ext-nacl)#remark we will want to rate limit ICMP traffic SW1(config-ext-nacl)#permit icmp any any echo SW1(config-ext-nacl)#permit icmp any any echo-reply SW1(config-ext-nacl)#permit icmp any any time-exceeded SW1(config-ext-nacl)#permit icmp any any unreachable SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#ip access-list extended CoPP_UNDESIRABLE SW1(config-ext-nacl)#remark management plane traffic that should not be received SW1(config-ext-nacl)#permit udp any any eq ntp SW1(config-ext-nacl)#permit udp any any eq snmp SW1(config-ext-nacl)#permit tcp any any eq 22 SW1(config-ext-nacl)#permit tcp any any eq 23 SW1(config-ext-nacl)#remark control plane traffic not configured on switch SW1(config-ext-nacl)#permit eigrp any any SW1(config-ext-nacl)#permit udp any any eq rip SW1(config-ext-nacl)#deny ip any any SW1(config-ext-nacl)#exit SW1(config)#ip access-list extended CoPP_DEFAULT SW1(config-ext-nacl)#permit ip any any SW1(config-ext-nacl)#exit Step 2: Configure class-maps referencing each of the ACLs. SW1(config)#class-map match-all CoPP_CRITICAL SW1(config-cmap)#match access-group name CoPP_CRITICAL SW1(config-cmap)#class-map match-any CoPP_IMPORTANT SW1(config-cmap)#match access-group name CoPP_IMPORTANT SW1(config-cmap)#match protocol arp SW1(config-cmap)#class-map match-all CoPP_NORMAL SW1(config-cmap)#match access-group name CoPP_NORMAL SW1(config-cmap)#class-map match-any CoPP_UNDESIRABLE SW1(config-cmap)#match access-group name CoPP_UNDESIRABLE SW1(config-cmap)#class-map match-all CoPP_DEFAULT SW1(config-cmap)#match access-group name CoPP_DEFAULT SW1(config-cmap)#exit Step 3: Configure a policy-map referencing the configured class-maps and apply appropriate bandwidth allowance and policing attributes. SW1(config)#policy-map CONTROL_PLANE_POLICY SW1(config-pmap)#class CoPP_CRITICAL SW1(config-pmap-c)#police 512000 8000 conform-action transmit exceed-action transmit SW1(config-pmap-c-police)#class CoPP_IMPORTANT SW1(config-pmap-c)#police 256000 4000 conform-action transmit exceed-action drop SW1(config-pmap-c-police)#class CoPP_NORMAL SW1(config-pmap-c)#police 128000 2000 conform-action transmit exceed-action drop SW1(config-pmap-c-police)#class CoPP_UNDESIRABLE SW1(config-pmap-c)#police 8000 1000 conform-action drop exceed-action drop SW1(config-pmap-c-police)#class CoPP_DEFAULT SW1(config-pmap-c)#police 64000 1000 conform-action transmit exceed-action drop SW1(config-pmap-c-police)#exit SW1(config-pmap-c)#exit SW1(config-pmap)#exit Step 4: Apply the policy-map to the control plane. SW1(config)#control-plane SW1(config-cp)#service-policy input CONTROL_PLANE_POLICY SW1(config-cp)#end
Check Content
Review the Cisco switch configuration to verify that is protects against known types of DoS attacks by employing organization-defined security safeguards. Step 1: Verify traffic types have been classified based on importance levels. The following is an example configuration: class-map match-all CoPP_CRITICAL match access-group name CoPP_CRITICAL class-map match-any CoPP_IMPORTANT match access-group name CoPP_IMPORTANT match protocol arp class-map match-all CoPP_NORMAL match access-group name CoPP_NORMAL class-map match-any CoPP_UNDESIRABLE match access-group name CoPP_UNDESIRABLE class-map match-all CoPP_DEFAULT match access-group name CoPP_DEFAULT Step 2: Review the access control lists (ACLs) referenced by the class maps to determine if the traffic is being classified appropriately. The following is an example configuration: ip access-list extended CoPP_CRITICAL remark our control plane adjacencies are critical permit ospf host [OSPF neighbor A] any permit ospf host [OSPF neighbor B] any permit pim host [PIM neighbor A] any permit pim host [PIM neighbor B] any permit pim host [RP addr] any permit igmp any 224.0.0.0 15.255.255.255 deny ip any any ip access-list extended CoPP_IMPORTANT permit tcp host [TACACS server] eq tacacs any permit tcp [management subnet] 0.0.0.255 any eq 22 permit udp host [SNMP manager] any eq snmp permit udp host [NTP server] eq ntp any deny ip any any ip access-list extended CoPP_NORMAL remark we will want to rate limit ICMP traffic permit icmp any any echo permit icmp any any echo-reply permit icmp any any time-exceeded permit icmp any any unreachable deny ip any any ip access-list extended CoPP_UNDESIRABLE remark other management plane traffic that should not be received permit udp any any eq ntp permit udp any any eq snmp permit tcp any any eq 22 permit tcp any any eq 23 remark other control plane traffic not configured on switch permit eigrp any any permit udp any any eq rip deny ip any any ip access-list extended CoPP_DEFAULT permit ip any any Note: Explicitly defining undesirable traffic with ACL entries enables the network operator to collect statistics. Excessive ARP packets can potentially monopolize Route Processor resources, starving other important processes. Currently, ARP is the only Layer 2 protocol that can be specifically classified using the match protocol command. Step 3: Review the policy-map to determine if the traffic is being policed appropriately for each classification. The following is an example configuration: policy-map CONTROL_PLANE_POLICY class CoPP_CRITICAL police 512000 8000 conform-action transmit exceed-action transmit class CoPP_IMPORTANT police 256000 4000 conform-action transmit exceed-action drop class CoPP_NORMAL police 128000 2000 conform-action transmit exceed-action drop class CoPP_UNDESIRABLE police 8000 1000 conform-action drop exceed-action drop class CoPP_DEFAULT police 64000 1000 conform-action transmit exceed-action drop Step 4: Verify that the Control Plane Policing (CoPP) policy is enabled. The following is an example configuration: control-plane service-policy input CONTROL_PLANE_POLICY Note: Control Plane Protection (CPPr) can be used to filter as well as police control plane traffic destined to the RP. CPPr is very similar to CoPP and has the ability to filter and police traffic using finer granularity by dividing the aggregate control plane into three separate categories: 1) host, 2) transit, and 3) CEF-exception. Hence, a separate policy-map could be configured for each traffic category. If the Cisco switch is not configured to protect against known types of DoS attacks by employing organization-defined security safeguards, this is a finding.
The Cisco switch must be configured to restrict traffic destined to itself.
Discussion
The route processor handles traffic destined to the switch. This is the key component used to build forwarding paths and is instrumental with all network management functions. Hence, any disruption or denial-of-service (DoS) attack to the route processor can result in mission-critical network outages.
Fix Text
Step 1: Configure the ACL for any external interfaces as shown in the example below: SW1(config)#ip access-list extended EXTERNAL_ACL SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply SW1(config-ext-nacl)#deny ip any host x.11.1.1 log-input SW1(config-ext-nacl)#permit … … … … SW1(config-ext-nacl)#deny ip any any log-input Step 2: Configure the ACL for any external interfaces as shown in the example below: SW1(config)#ip access-list extended INTERNAL_ACL SW1(config-ext-nacl)#permit ospf host 10.1.12.1 host 10.1.12.2 SW1(config-ext-nacl)#permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq 22 SW1(config-ext-nacl)#permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq tacacs SW1(config-ext-nacl)#permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq snmp SW1(config-ext-nacl)#permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq ntp SW1(config-ext-nacl)#deny ip any host 10.1.12.2 log-input SW1(config-ext-nacl)#permit … … … … SW1(config-ext-nacl)#permit ip any any log-input SW1(config-ext-nacl)#exit Note: Best practice is to configure the ACL statements relative to traffic destined to the switch first followed by ACL statements for transit traffic. Step 3: Apply the ACLs to the appropriate interface as shown in the example below: SW1(config)#int g0/2 SW1(config-if)#ip access-group EXTERNAL_ACL in SW1(config)#int g0/3 SW1(config-if)#ip access-group INTERNAL_ACL in
Check Content
Review the external and internal access control lists (ACLs) to verify that the switch is configured to only allow specific management and control plane traffic from specific sources destined to itself. Step 1: Verify that ACLs have been configured as shown in the example below that matches expected control plane and management plane traffic. With the exception of Internet Control Message Protocol (ICMP), all other traffic destined to the switch should be dropped. ip access-list extended EXTERNAL_ACL permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp host x.11.1.1 host x.11.1.2 echo-reply deny ip any host x.11.1.1 log-input permit … … … … deny ip any any log-input ip access-list extended INTERNAL_ACL permit icmp any any permit ospf host 10.1.12.1 host 10.1.12.2 permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq 22 permit tcp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq tacacs permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq snmp permit udp 10.2.1.0 0.0.0.255 host 10.1.12.2 eq ntp deny ip any host 10.1.12.2 log-input permit … … … … deny ip any any log-input Note: For the internal ACL example, all switches within the hypothetical network (10.1.0.0/16) have been configured to use the loopback address to source all management traffic (not shown); hence, the loopbacks are the only allowable destination address for management traffic. In addition, all management traffic destined to the switch must originate from the management network (10.2.1.0/24). With the exception of link-local control plane traffic and ICMP, all other traffic destined to any physical interface address will be dropped. Step 2: Verify that the ACL has been applied to the appropriate interface as shown in the example below: interface GigabitEthernet0/2 no switchport ip address x.11.1.2 255.255.255.254 ip access-group EXTERNAL_ACL in interface GigabitEthernet0/3 no switchport ip address 10.1.12.2 255.255.255.0 ip access-group INTERNAL_ACL in If the switch is not configured to restrict traffic destined to itself, this is a finding.
The Cisco switch must be configured to drop all fragmented Internet Control Message Protocol (ICMP) packets destined to itself.
Discussion
Fragmented ICMP packets can be generated by hackers for denial-of-service (DoS) attacks such as Ping O' Death and Teardrop. It is imperative that all fragmented ICMP packets are dropped.
Fix Text
Configure the external and internal ACLs to drop all fragmented ICMP packets destined to itself as shown in the example below: SW1(config)#ip access-list extended EXTERNAL_ACL SW1(config-ext-nacl)#deny icmp any host x.11.1.2 fragments SW1(config)#ip access-list extended INTERNAL_ACL SW1(config-ext-nacl)#deny icmp any host 10.1.12.2 fragments Note: Ensure the above statement is before any permit statements for ICMP.
Check Content
Review the external and internal access control lists (ACLs) to verify that the switch is configured drop all fragmented ICMP packets destined to itself. ip access-list extended EXTERNAL_ACL deny icmp any host x.11.1.2 fragments permit icmp host x.11.1.1 host x.11.1.2 echo … … deny ip any any ! ip access-list extended INTERNAL_ACL deny icmp any host 10.1.12.2 fragments permit icmp any any Note: Ensure the statement to deny ICMP fragments is before any permit statements for ICMP. If the switch is not configured to drop all fragmented ICMP packets destined to itself, this is a finding.
The Cisco switch must be configured to have gratuitous ARP disabled on all external interfaces.
Discussion
A gratuitous ARP is an ARP broadcast in which the source and destination MAC addresses are the same. It is used to inform the network about a host IP address. A spoofed gratuitous ARP message can cause network mapping information to be stored incorrectly, causing network malfunction.
Fix Text
Disable gratuitous ARP as shown in the example below: SW1(config)#no ip gratuitous-arps
Check Content
Review the configuration to determine if gratuitous ARP is disabled. The following command should not be found in the switch configuration: ip gratuitous-arps Note: With Cisco IOS, gratuitous ARP is enabled and disabled globally. If gratuitous ARP is enabled on any external interface, this is a finding.
The Cisco switch must be configured to have IP directed broadcast disabled on all interfaces.
Discussion
An IP directed broadcast is a datagram sent to the broadcast address of a subnet that is not directly attached to the sending machine. The directed broadcast is routed through the network as a unicast packet until it arrives at the target subnet, where it is converted into a link-layer broadcast. Because of the nature of the IP addressing architecture, only the last switch in the chain, which is connected directly to the target subnet, can conclusively identify a directed broadcast. IP directed broadcasts are used in the extremely common and popular smurf, or denial-of-service (DoS), attacks. In a smurf attack, the attacker sends Internet Control Message Protocol (ICMP) echo requests from a falsified source address to a directed broadcast address, causing all the hosts on the target subnet to send replies to the falsified source. By sending a continuous stream of such requests, the attacker can create a much larger stream of replies, which can completely inundate the host whose address is being falsified. This service should be disabled on all interfaces when not needed to prevent smurf and DoS attacks. Directed broadcast can be enabled on internal-facing interfaces to support services such as Wake-On-LAN. Case scenario may also include support for legacy applications where the content server and the clients do not support multicast. The content servers send streaming data using UDP broadcast. Used in conjunction with the IP multicast helper-map feature, broadcast data can be sent across a multicast topology. The broadcast streams are converted to multicast and vice versa at the first-hop switches and last-hop switches before entering and leaving the multicast transit area respectively. The last-hop switch must convert the multicast to broadcast. Hence, this interface must be configured to forward a broadcast packet (i.e., a directed broadcast address is converted to the all nodes broadcast address).
Fix Text
Disable IP directed broadcast on all interfaces as shown in the example below: SW1(config)#int g0/1 SW1(config-if)#no ip directed-broadcast SW1(config)#int vlan11 SW1(config-if)#no ip directed-broadcast
Check Content
Review the switch configuration to determine if IP directed broadcast is disabled. The IP directed broadcast command must not be found on any interface as shown in the example below: interface GigabitEthernet0/1 no switchport ip address x.x.x.x 255.255.255.0 ip directed-broadcast … … … Interface Vlan11 no switchport ip address x.x.x.x 255.255.255.0 ip directed-broadcast If IP directed broadcast is not disabled on all interfaces, this is a finding.
The Cisco switch must be configured to have Internet Control Message Protocol (ICMP) unreachable messages disabled on all external interfaces.
Discussion
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Switches automatically send ICMP messages under a wide variety of conditions. Host unreachable ICMP messages are commonly used by attackers for network mapping and diagnosis.
Fix Text
Step 1: Disable ip unreachables on all external interfaces. SW1(config)#int g0/1 SW1(config-if)#no ip unreachables Step 2: Disable ip unreachables on the Null0 interface if it is used to backhole packets. SW1(config-if)#int null 0 SW1(config-if)#no ip unreachables Alternative - DODIN Backbone: Configure the PE switch to rate limit ICMP unreachable messages as shown in the example below: SW1(config)#ip icmp rate-limit unreachable df 100 SW1(config)#ip icmp rate-limit unreachable 100000 SW1(config)#end Alternative - Non-DODIN Backbone: An alternative for non-backbone networks (e.g., enclave, base, camp, etc.) is to filter messages generated by the switch and silently drop ICMP Administratively Prohibited and Host Unreachable messages using the following configuration steps: Step 1: Configure ACL to include ICMP Type 3 Code 1 (Host Unreachable) and Code 13 (Administratively Prohibited) as shown in the example below: SW1(config)#ip access-list ext ICMP_T3C1C13 SW1(config-ext-nacl)#permit icmp any any host-unreachable SW1(config-ext-nacl)#permit icmp any any administratively-prohibited SW1(config-ext-nacl)#exit Step 2: Create a route-map to forward these ICMP messages to the Null0 interface. SW1(config)#route-map LOCAL_POLICY SW1(config-route-map)#match ip address ICMP_T3C1C13 SW1(config-route-map)#set interface Null0 SW1(config-route-map)#exit Step 3: Configure no ip unreachables on the Null0 interface. SW1(config)#int null 0 SW1(config-if)#no ip unreachables SW1(config-if)#exit Step 4: Apply the policy to filter messages generated by the switch. SW1(config)#ip local policy route-map LOCAL_POLICY SW1(config)#end
Check Content
Review the configuration to verify the no ip unreachables command has been configured on all external interfaces as shown in the configuration example below: interface GigabitEthernet0/1 ip address x.x.x.x 255.255.255.0 no ip unreachables If ICMP unreachable notifications are sent from any external or null0 interface, this is a finding. Alternative - DODIN Backbone: Verify that the PE switch is configured to rate limit ICMP unreachable messages as shown in the example below: ip icmp rate-limit unreachable 60000 ip icmp rate-limit unreachable DF 1000 Note: In the example above, packet-too-big message (ICMP Type 3 Code 4) can be sent once every second, while all other destination unreachable messages can be sent once every minute. This will avoid disrupting Path MTU Discovery for traffic traversing the backbone while mitigating the risk of an ICMP unreachable DoS attack. If the PE switch is not configured to rate limit ICMP unreachable messages, this is a finding.
The Cisco switch must be configured to have Internet Control Message Protocol (ICMP) mask reply messages disabled on all external interfaces.
Discussion
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Switches automatically send ICMP messages under a wide variety of conditions. Mask Reply ICMP messages are commonly used by attackers for network mapping and diagnosis.
Fix Text
Disable ip mask-reply on all external interfaces as shown below: SW1(config)#int g0/1 SW1(config-if)#no ip mask-reply
Check Content
Review the switch configuration and verify that ip mask-reply command is not enabled on any external interfaces as shown in the example below: interface GigabitEthernet0/1 ip address x.x.x.x 255.255.255.0 ip mask-reply If the ip mask-reply command is configured on any external interface, this is a finding.
The Cisco switch must be configured to have Internet Control Message Protocol (ICMP) redirect messages disabled on all external interfaces.
Discussion
The ICMP supports IP traffic by relaying information about paths, routes, and network conditions. Switches automatically send ICMP messages under a wide variety of conditions. Redirect ICMP messages are commonly used by attackers for network mapping and diagnosis.
Fix Text
Disable ICMP redirects on all external interfaces as shown in the example below: SW1(config)#int g0/1 SW1(config-if)#no ip redirects
Check Content
Review the switch configuration to verify that the no ip redirects command has been configured on all external interfaces as shown in the example below: interface GigabitEthernet0/1 ip address x.x.x.x 255.255.255.0 no ip redirects If ICMP Redirect messages are enabled on any external interfaces, this is a finding.
The Cisco switch must be configured to log all packets that have been dropped at interfaces via an access control list (ACL).
Discussion
Auditing and logging are key components of any security architecture. It is essential for security personnel to know what is being done or attempted to be done, and by whom, to compile an accurate risk assessment. Auditing the actions on network devices provides a means to recreate an attack or identify a configuration mistake on the device.
Fix Text
Configure ACLs to log packets that are dropped as shown in the example below: SW1(config)#ip access-list extended INGRESS_FILTER … … … SW1(config-ext-nacl)#deny ip any any log
Check Content
Review all ACLs used to filter traffic and verify that packets being dropped at interfaces via an ACL are logged as shown in the configuration below: ip access-list extended INGRESS_FILTER permit tcp any any established permit tcp any host x.11.1.5 eq www permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp any any echo-reply … … … deny ip any any log If packets being dropped are not logged, this is a finding.
The Cisco switch must be configured to produce audit records containing information to establish where the events occurred.
Discussion
Without establishing where events occurred, it is impossible to establish, correlate, and investigate the events leading up to an outage or attack. To compile an accurate risk assessment and provide forensic analysis, it is essential for security personnel to know where events occurred, such as switch components, modules, device identifiers, node names, and functionality. Associating information about where the event occurred within the network provides a means of investigating an attack, recognizing resource utilization or capacity thresholds, or identifying an improperly configured switch.
Fix Text
Configure the switch to log events containing information to establish where the events occurred as shown in the example below: SW1(config)#ip access-list extended INGRESS_FILTER … … … SW1(config-ext-nacl)#deny ip any any log-input
Check Content
Review the switch configuration to verify that events are logged containing information to establish where the events occurred as shown in the example below: ip access-list extended INGRESS_FILTER permit tcp any any established permit tcp any host x.11.1.5 eq www permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp any any echo-reply … … … deny ip any any log-input Note: When the log-input parameter is configured on deny statements, the log record will contain the interface where the ingress packet has been dropped. If the switch is not configured to produce audit records containing information to establish to establish where the events occurred, this is a finding.
The Cisco switch must be configured to produce audit records containing information to establish the source of the events.
Discussion
Without establishing the source of the event, it is impossible to establish, correlate, and investigate the events leading up to an outage or attack. To compile an accurate risk assessment and provide forensic analysis, security personnel need to know the source of the event. In addition to logging where events occur within the network, the audit records must also identify sources of events such as IP addresses, processes, and node or device names.
Fix Text
Configure the switch to log events containing information to establish where the events occurred as shown in the example below: SW1(config)#ip access-list extended INGRESS_FILTER … … … SW1(config-ext-nacl)#deny ip any any log-input
Check Content
Review the switch configuration to verify that events are logged containing information to establish the source of the events as shown in the example below: ip access-list extended INGRESS_FILTER permit tcp any any established permit tcp any host x.11.1.5 eq www permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp any any echo-reply … … … deny ip any any log-input Note: When the log-input parameter is configured on deny statements, the log record will contain the Layer 2 address of the forwarding device for any packet being dropped. If the switch is not configured to produce audit records containing information to establish the source of the events, this is a finding.
The Cisco switch must be configured to disable the auxiliary port unless it is connected to a secured modem providing encryption and authentication.
Discussion
The use of POTS lines to modems connecting to network devices provides clear text of authentication traffic over commercial circuits that could be captured and used to compromise the network. Additional war dial attacks on the device could degrade the device and the production network. Secured modem devices must be able to authenticate users and must negotiate a key exchange before full encryption takes place. The modem will provide full encryption capability (Triple DES) or stronger. The technician who manages these devices will be authenticated using a key fob and granted access to the appropriate maintenance port; thus, the technician will gain access to the managed device. The token provides a method of strong (two-factor) user authentication. The token works in conjunction with a server to generate one-time user passwords that will change values at second intervals. The user must know a personal identification number (PIN) and possess the token to be allowed access to the device.
Fix Text
Disable the auxiliary port. SW2(config)#line aux 0 SW2(config-line)#no exec SW2(config-line)#transport input none
Check Content
Review the configuration and verify that the auxiliary port is disabled unless a secured modem providing encryption and authentication is connected to it. line aux 0 no exec Note: transport input none is the default; hence, it will not be shown in the configuration. If the auxiliary port is not disabled or is not connected to a secured modem when it is enabled, this is a finding.
The Cisco perimeter switch must be configured to deny network traffic by default and allow network traffic by exception.
Discussion
A deny-all, permit-by-exception network communications traffic policy ensures that only connections that are essential and approved are allowed. This requirement applies to both inbound and outbound network communications traffic. All inbound and outbound traffic must be denied by default. Firewalls and perimeter switches should only allow traffic through that is explicitly permitted. The initial defense for the internal network is to block any traffic at the perimeter that is attempting to make a connection to a host residing on the internal network. In addition, allowing unknown or undesirable outbound traffic by the firewall or switch will establish a state that will permit the return of this undesirable traffic inbound.
Fix Text
Step 1: Configure an inbound ACL to deny all other traffic by default as shown in the example below: SW1(config)#ip access-list extended EXTERNAL_ACL SW1(config-ext-nacl)#permit tcp any any established SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply … … … SW1(config-ext-nacl)#deny ip any any log-input Step 2: Apply the ingress filter to all external interfaces. SW1(config)#int g0/2 SW1(config-if)#ip access-group EXTERNAL_ACL in
Check Content
Review the switch configuration to verify that the inbound access control list (ACL) applied to all external interfaces is configured to allow specific ports and protocols and deny all other traffic. Step 1: Verify that an inbound ACL is applied to all external interfaces as shown in the example below: interface GigabitEthernet0/2 ip address x.11.1.2 255.255.255.254 ip access-group EXTERNAL_ACL in Step 2: Review the inbound ACL to verify that it is configured to deny all other traffic that is not explicitly allowed. ip access-list extended EXTERNAL_ACL permit tcp any any established permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp host x.11.1.1 host x.11.1.2 echo-reply … … … deny ip any any log-input If the ACL is not configured to allow specific ports and protocols and deny all other traffic, this is a finding. If the ACL is not configured inbound on all external interfaces, this is a finding.
The Cisco perimeter switch must be configured to enforce approved authorizations for controlling the flow of information between interconnected networks in accordance with applicable policy.
Discussion
Information flow control regulates authorized information to travel within a network and between interconnected networks. Controlling the flow of network traffic is critical so it does not introduce any unacceptable risk to the network infrastructure or data. An example of a flow control restriction is blocking outside traffic claiming to be from within the organization. For most switches, internal information flow control is a product of system design.
Fix Text
Step 1: Configure an ACL to allow or deny traffic as shown in the example below: R1(config)#ip access-list extended FILTER_PERIMETER R1(config-ext-nacl)#permit tcp any any established R1(config-ext-nacl)#permit tcp host x.12.1.9 host x.12.1.10 eq bgp R1(config-ext-nacl)#permit tcp host x.12.1.9 eq bgp host x.12.1.10 R1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo R1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo-reply R1(config-ext-nacl)#permit tcp any host x.12.1.22 eq www R1(config-ext-nacl)#deny ip any any log-input R1(config-ext-nacl)#exit Step 2: Apply the ACL inbound on all external interfaces. R2(config)#int g0/0 R1(config-if)#ip access-group FILTER_PERIMETER in R1(config-if)#end
Check Content
Review the switch configuration to verify that access control lists (ACLs) are configured to allow or deny traffic for specific source and destination addresses as well as ports and protocols. In the example below, ICMP echo and echo-reply packets are allowed for troubleshooting connectivity. WWW traffic is permitted inbound to the NIPRNet host-facing web server (x.12.1.22). interface GigabitEthernet0/1 description Link to DISN ip address x.12.1.10 255.255.255.0 ip access-group FILTER_PERIMETER in … … … ip access-list extended FILTER_PERIMETER permit tcp any any established permit icmp host x.12.1.9 host x.12.1.10 echo permit icmp host x.12.1.9 host x.12.1.10 echo-reply permit tcp any host x.12.1.22 eq www deny ip any any log-input If the switch is not configured to enforce approved authorizations for controlling the flow of information between interconnected networks, this is a finding.
The Cisco perimeter switch must be configured to only allow incoming communications from authorized sources to be routed to authorized destinations.
Discussion
Unrestricted traffic may contain malicious traffic that poses a threat to an enclave or to other connected networks. Additionally, unrestricted traffic may transit a network, which uses bandwidth and other resources. Traffic can be restricted directly by an access control list (ACL), which is a firewall function, or by Policy Routing. Policy Routing is a technique used to make routing decisions based on a number of different criteria other than just the destination network, including source or destination network, source or destination address, source or destination port, protocol, packet size, and packet classification. This overrides the switch's normal routing procedures used to control the specific paths of network traffic. It is normally used for traffic engineering but can also be used to meet security requirements; for example, traffic that is not allowed can be routed to the Null0 or discard interface. Policy Routing can also be used to control which prefixes appear in the routing table. This requirement is intended to allow network administrators the flexibility to use whatever technique is most effective.
Fix Text
Configure the switch to allow only incoming communications from authorized sources to be routed to authorized destinations. SW1(config)#ip access-list extended FILTER_PERIMETER SW1(config-ext-nacl)#permit udp host x.12.1.9 host x.12.1.21 eq ntp SW1(config-ext-nacl)#end
Check Content
Review the switch configuration to determine if the switch allows only incoming communications from authorized sources to be routed to authorized destinations. The hypothetical example below allows inbound NTP from server x.1.12.9 only to host x.12.1.21. ip access-list extended FILTER_PERIMETER permit tcp any any established … … … permit udp host x.12.1.9 host x.12.1.21 eq ntp deny ip any any log-input If the switch does not restrict incoming communications to allow only authorized sources and destinations, this is a finding.
The Cisco perimeter switch must be configured to block inbound packets with source Bogon IP address prefixes.
Discussion
Packets with Bogon IP source addresses should never be allowed to traverse the IP core. Bogon IP networks are RFC1918 addresses or address blocks that have never been assigned by the IANA or have been reserved.
Fix Text
Configure the perimeter to block inbound packets with Bogon source addresses. Step 1: Configure an ACL containing the current Bogon prefixes as shown below: SW1(config)#ip access-list extended FILTER_PERIMETER SW1(config-ext-nacl)#deny ip 0.0.0.0 0.255.255.255 any log-input SW1(config-ext-nacl)#deny ip 10.0.0.0 0.255.255.255 any log-input SW1(config-ext-nacl)#deny ip 100.64.0.0 0.63.255.255 any log-input SW1(config-ext-nacl)#deny ip 127.0.0.0 0.255.255.255 any log-input SW1(config-ext-nacl)#deny ip 169.254.0.0 0.0.255.255 any log-input SW1(config-ext-nacl)#deny ip 172.16.0.0 0.15.255.255 any log-input SW1(config-ext-nacl)#deny ip 192.0.0.0 0.0.0.255 any log-input SW1(config-ext-nacl)#deny ip 192.0.2.0 0.0.0.255 any log-input SW1(config-ext-nacl)#deny ip 192.168.0.0 0.0.255.255 any log-input SW1(config-ext-nacl)#deny ip 198.18.0.0 0.1.255.255 any log-input SW1(config-ext-nacl)#deny ip 198.51.100.0 0.0.0.255 any log-input SW1(config-ext-nacl)#deny ip 203.0.113.0 0.0.0.255 any log-input SW1(config-ext-nacl)#deny ip 224.0.0.0 31.255.255.255 any log-input SW1(config-ext-nacl)#deny ip 240.0.0.0 31.255.255.255 any log-input SW1(config-ext-nacl)#permit tcp any any established SW1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo SW1(config-ext-nacl)#permit icmp host x.12.1.9 host x.12.1.10 echo-reply … … … SW1(config-ext-nacl)#deny ip any any log-input SW1(config-ext-nacl)#end Step 2: Apply the ACL inbound on all external interfaces. SW1(config)#int g0/0 SW1(config-if)#ip access-group FILTER_PERIMETER in SW1(config-if)#end
Check Content
Review the switch configuration to verify that an ingress access control list (ACL) applied to all external interfaces is blocking packets with Bogon source addresses. Step 1: Verify that an ACL has been configured containing the current Bogon prefixes as shown in the example below: ip access-list extended FILTER_PERIMETER deny ip 0.0.0.0 0.255.255.255 any log-input deny ip 10.0.0.0 0.255.255.255 any log-input deny ip 100.64.0.0 0.63.255.255 any log-input deny ip 127.0.0.0 0.255.255.255 any log-input deny ip 169.254.0.0 0.0.255.255 any log-input deny ip 172.16.0.0 0.15.255.255 any log-input deny ip 192.0.0.0 0.0.0.255 any log-input deny ip 192.0.2.0 0.0.0.255 any log-input deny ip 192.168.0.0 0.0.255.255 any log-input deny ip 198.18.0.0 0.1.255.255 any log-input deny ip 198.51.100.0 0.0.0.255 any log-input deny ip 203.0.113.0 0.0.0.255 any log-input deny ip 224.0.0.0 31.255.255.255 any log-input permit tcp any any established permit icmp host x.12.1.9 host x.12.1.10 echo permit icmp host x.12.1.9 host x.12.1.10 echo-reply … … … deny ip any any log-input Step 2: Verify that the inbound ACL applied to all external interfaces will block all traffic from Bogon source addresses. interface GigabitEthernet0/1 description Link to DISN ip address x.12.1.10 255.255.255.254 ip access-group FILTER_PERIMETER in If the switch is not configured to block inbound packets with source Bogon IP address prefixes, this is a finding.
The Cisco perimeter switch must be configured to restrict it from accepting outbound IP packets that contain an illegitimate address in the source address field via egress filter or by enabling Unicast Reverse Path Forwarding (uRPF).
Discussion
A compromised host in an enclave can be used by a malicious platform to launch cyberattacks on third parties. This is a common practice in "botnets", which are a collection of compromised computers using malware to attack other computers or networks. DDoS attacks frequently leverage IP source address spoofing to send packets to multiple hosts that in turn will then send return traffic to the hosts with the IP addresses that were forged. This can generate significant amounts of traffic. Therefore, protection measures to counteract IP source address spoofing must be taken. When uRPF is enabled in strict mode, the packet must be received on the interface that the device would use to forward the return packet, thereby mitigating IP source address spoofing.
Fix Text
Configure the switch to ensure that an egress ACL or uRPF is configured on internal interfaces to restrict the switch from accepting any outbound IP packet that contains an illegitimate address in the source field. The example below enables uRPF. SW1(config)#int g0/1 SW1(config-if)#ip verify unicast source reachable-via rx
Check Content
Review the switch configuration to verify that uRPF or an egress ACL has been configured on all internal interfaces to restrict the switch from accepting outbound IP packets that contain an illegitimate address in the source address field. uRPF example: interface GigabitEthernet0/1 description downstream link to LAN ip address 10.1.25.5 255.255.255.0 ip verify unicast source reachable-via rx Egress ACL example: interface GigabitEthernet0/1 description downstream link to LAN ip address 10.1.25.5 255.255.255.0 ip access-group EGRESS_FILTER in … … … ip access-list extended EGRESS_FILTER permit udp 10.1.15.0 0.0.0.255 any eq domain permit tcp 10.1.15.0 0.0.0.255 any eq ftp permit tcp 10.1.15.0 0.0.0.255 any eq ftp-data permit tcp 10.1.15.0 0.0.0.255 any eq www permit icmp 10.1.15.0 0.0.0.255 any permit icmp 10.1.15.0 0.0.0.255 any echo deny ip any any If uRPF or an egress ACL to restrict the switch from accepting outbound IP packets that contain an illegitimate address in the source address field has not been configured on all internal interfaces in an enclave, this is a finding.
The Cisco perimeter switch must be configured to filter traffic destined to the enclave in accordance with the guidelines contained in DoD Instruction 8551.1.
Discussion
Vulnerability assessments must be reviewed by the System Administrator, and protocols must be approved by the Information Assurance (IA) staff before entering the enclave. Access control lists (ACLs) are the first line of defense in a layered security approach. They permit authorized packets and deny unauthorized packets based on port or service type. They enhance the posture of the network by not allowing packets to reach a potential target within the security domain. The lists provided are highly susceptible ports and services that should be blocked or limited as much as possible without adversely affecting customer requirements. Auditing packets attempting to penetrate the network that are stopped by an ACL will allow network administrators to broaden their protective ring and more tightly define the scope of operation. If the perimeter is in a Deny-by-Default posture and what is allowed through the filter is in accordance with DoD Instruction 8551.1, and if the permit rule is explicitly defined with explicit ports and protocols allowed, then all requirements related to PPS being blocked would be satisfied.
Fix Text
Configure the switch to use an inbound ACL on all external interfaces as shown in the example below to restrict traffic in accordance with the guidelines contained in DoD Instruction 8551.1. SW1(config)#ip access-list extended EXTERNAL_ACL_INBOUND SW1(config-ext-nacl)#permit tcp any any established SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo SW1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply … … < must be in accordance with DoD Instruction 8551.1> … SW1(config-ext-nacl)#deny ip any any log-input SW1(config-ext-nacl)#exit SW1(config)#int g0/2 SW1(config-if)#ip access-group EXTERNAL_ACL_INBOUND in
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Review the switch configuration to verify that the ingress ACL is in accordance with DoD 8551.1. Step 1: Verify that an inbound ACL is configured on all external interfaces. interface GigabitEthernet0/2 ip address x.11.1.2 255.255.255.254 ip access-group EXTERNAL_ACL_INBOUND in Step 2. Review the inbound ACL to verify that it is filtering traffic in accordance with DoD 8551.1. ip access-list extended EXTERNAL_ACL_INBOUND permit tcp any any established permit icmp host x.11.1.1 host x.11.1.2 echo permit icmp host x.11.1.1 host x.11.1.2 echo-reply … … < must be in accordance with DoD Instruction 8551.1> … deny ip any any log-input If the switch does not filter traffic in accordance with the guidelines contained in DoD 8551.1, this is a finding.
The Cisco perimeter switch must be configured to filter ingress traffic at the external interface on an inbound direction.
Discussion
Access lists are used to separate data traffic into that which it will route (permitted packets) and that which it will not route (denied packets). Secure configuration of switches makes use of access lists to restrict access to services on the switch itself as well as filter traffic passing through the switch. Inbound versus Outbound: Some operating systems' default access lists are applied to the outbound queue. The more secure solution is to apply the access list to the inbound queue for three reasons: - The switch can protect itself before damage is inflicted. - The input port is still known and can be filtered on. - It is more efficient to filter packets before routing them.
Fix Text
Configure the switch to use an inbound ACL on all external interfaces as shown in the example below: SW1(config)#int g0/2 SW1(config-if)#ip access-group EXTERNAL_ACL_INBOUND in
Check Content
Review the switch configuration to verify that an inbound ACL is configured on all external interfaces as shown in the example below: interface GigabitEthernet0/2 ip address x.11.1.2 255.255.255.254 ip access-group EXTERNAL_ACL_INBOUND in If the switch is not configured to filter traffic entering the network at all external interfaces in an inbound direction, this is a finding.
The Cisco perimeter switch must be configured to filter egress traffic at the internal interface on an inbound direction.
Discussion
Access lists are used to separate data traffic into that which it will route (permitted packets) and that which it will not route (denied packets). Secure configuration of switches makes use of access lists to restrict access to services on the switch itself as well as filter traffic passing through the switch. Inbound versus Outbound: Some operating systems' default access lists are applied to the outbound queue. The more secure solution is to apply the access list to the inbound queue for three reasons: - The switch can protect itself before damage is inflicted. - The input port is still known and can be filtered on. - It is more efficient to filter packets before routing them.
Fix Text
Configure the switch to use an inbound ACL on all internal interfaces as shown in the example below: SW1(config)#int g0/2 SW1(config-if)#ip access-group EGRESS_FILTER in
Check Content
Review the switch configuration to verify that the egress access control list (ACL) is bound to the internal interface in an inbound direction. interface interface GigabitEthernet0/2 description downstream link to LAN ip address 10.1.25.5 255.255.255.0 ip access-group EGRESS_FILTER in If the switch is not configured to filter traffic leaving the network at the internal interface in an inbound direction, this is a finding.
The Cisco perimeter switch must be configured to block all packets with any IP options.
Discussion
Packets with IP options are not fast switched and henceforth must be punted to the switch processor. Hackers who initiate denial-of-service (DoS) attacks on switches commonly send large streams of packets with IP options. Dropping the packets with IP options reduces the load of IP options packets on the switch. The end result is a reduction in the effects of the DoS attack on the switch and on downstream switches.
Fix Text
Configure the switch to drop all packets with IP options. SW1(config)#ip access-list extended EXTERNAL_ACL SW1(config-ext-nacl)#15 deny ip any any option any-options
Check Content
Review the switch configuration to determine if it will block all packets with IP options. ip access-list extended EXTERNAL_ACL permit tcp any any established deny ip any any option any-options permit … … … … deny ip any any log-input If the switch is not configured to drop all packets with IP options, this is a finding.
The Cisco perimeter switch must be configured to have Cisco Discovery Protocol (CDP) disabled on all external interfaces.
Discussion
CDP is a Cisco proprietary neighbor discovery protocol used to advertise device capabilities, configuration information, and device identity. CDP is media-and-protocol-independent as it runs over Layer 2; therefore, two network nodes that support different Layer 3 protocols can still learn about each other. Allowing CDP messages to reach external network nodes provides an attacker a method to obtain information of the network infrastructure that can be useful to plan an attack.
Fix Text
Disable CDP on all external interfaces via no cdp enable command or disable CDP globally via no cdp run command.
Check Content
Step 1: Verify if CDP is enabled globally as shown below: cdp run By default, CDP is not enabled globally or on any interface. If CDP is enabled globally, proceed to Step 2. Step 2: Verify CDP is not enabled on any external interface as shown in the example below: interface GigabitEthernet2 ip address z.1.24.4 255.255.255.252 … … … cdp enable If CDP is enabled on any external interface, this is a finding.
The Cisco perimeter switch must be configured to have Proxy ARP disabled on all external interfaces.
Discussion
When Proxy ARP is enabled on a switch, it allows that switch to extend the network (at Layer 2) across multiple interfaces (LAN segments). Because proxy ARP allows hosts from different LAN segments to look like they are on the same segment, proxy ARP is only safe when used between trusted LAN segments. Attackers can leverage the trusting nature of proxy ARP by spoofing a trusted host and then intercepting packets. Proxy ARP should always be disabled on switch interfaces that do not require it unless the switch is being used as a LAN bridge.
Fix Text
Disable Proxy ARP on all external interfaces as shown in the example below: SW1(config)#int g0/1 SW1(config-if)#no ip proxy-arp
Check Content
Review the switch configuration to determine if IP Proxy ARP is disabled on all external interfaces as shown in the example below: interface GigabitEthernet0/1 description link to DISN ip address x.1.12.2 255.255.255.252 no ip proxy-arp Note: By default, Proxy ARP is enabled on all interfaces; hence, if enabled, it will not be shown in the configuration. If IP Proxy ARP is enabled on any external interface, this is a finding.
The Cisco perimeter switch must be configured to block all outbound management traffic.
Discussion
For in-band management, the management network must have its own subnet in order to enforce control and access boundaries provided by Layer 3 network nodes, such as switches and firewalls. Management traffic between the managed network elements and the management network is routed via the same links and nodes as that used for production or operational traffic. Safeguards must be implemented to ensure that the management traffic does not leak past the perimeter of the managed network.
Fix Text
Configure the perimeter switch of the managed network with an outbound ACL on the egress interface to block all management traffic. Step 1: Configure an ACL to block egress management traffic. SW1(config)#ip access-list extended EXTERNAL_ACL_OUTBOUND SW1(config-ext-nacl)#deny tcp any any eq tacacs log-input SW1(config-ext-nacl)#deny tcp any any eq 22 log-input SW1(config-ext-nacl)#deny udp any any eq snmp log-input SW1(config-ext-nacl)#deny udp any any eq snmptrap log-input SW1(config-ext-nacl)#deny udp any any eq syslog log-input SW1(config-ext-nacl)#permit tcp any any eq www SW1(config-ext-nacl)#deny ip any any log-input SW1(config-ext-nacl)#exit Note: Permit commands would be configured to allow applicable outbound traffic. The example above is allowing web traffic. Step 2: Configure the external interfaces with the outbound ACL. SW1(config)#int g0/2 SW1(config-if)#ip access-group EXTERNAL_ACL_OUTBOUND out
Check Content
Verify that the perimeter switch of the managed network is configured with an outbound ACL on the egress interface to block all management traffic as shown in the example below: Step 1: Verify that all external interfaces has been configured with an outbound ACL as shown in the example below: interface GigabitEthernet0/2 description link to DISN ip address x.11.1.2 255.255.255.254 ip access-group EXTERNAL_ACL_OUTBOUND out Step 2: Verify that the outbound ACL discards management traffic as shown in the example below: ip access-list extended EXTERNAL_ACL_OUTBOUND deny tcp any any eq tacacs log-input deny tcp any any eq 22 log-input deny udp any any eq snmp log-input deny udp any any eq snmptrap log-input deny udp any any eq syslog log-input permit tcp any any eq www log-input deny ip any any log-input If management traffic is not blocked at the perimeter, this is a finding.
The Cisco perimeter switch must be configured to have Link Layer Discovery Protocol (LLDP) disabled on all external interfaces.
Discussion
LLDP is a neighbor discovery protocol used to advertise device capabilities, configuration information, and device identity. LLDP is media-and-protocol-independent as it runs over Layer 2; therefore, two network nodes that support different Layer 3 protocols can still learn about each other. Allowing LLDP messages to reach external network nodes provides an attacker a method to obtain information of the network infrastructure that can be useful to plan an attack.
Fix Text
Disable LLDP transmit on all external interfaces as shown in the example below: SW1(config)#int g0/1 SW1(config-if)#no lldp transmit
Check Content
Step 1: Verify LLDP is not enabled globally via the command. lldp run By default, LLDP is not enabled globally. If LLDP is enabled, proceed to Step 2. Step 2: Verify LLDP is not enabled on any external interface as shown in the example below: interface GigabitEthernet0/1 ip address x.1.12.1 255.255.255.252 no lldp transmit Note: LLDP is enabled by default on all interfaces once it is enabled globally; hence the command "lldp transmit" will not be visible on the interface configuration. If LLDP transmit is enabled on any external interface, this is a finding.
The Cisco switch must be configured to only permit management traffic that ingresses and egresses the out-of-band management (OOBM) interface.
Discussion
The OOBM access switch will connect to the management interface of the managed network elements. The management interface can be a true OOBM interface or a standard interface functioning as the management interface. In either case, the management interface of the managed network element will be directly connected to the OOBM network. An OOBM interface does not forward transit traffic, thereby providing complete separation of production and management traffic. Since all management traffic is immediately forwarded into the management network, it is not exposed to possible tampering. The separation also ensures that congestion or failures in the managed network do not affect the management of the device. If the device does not have an OOBM port, the interface functioning as the management interface must be configured so that management traffic does not leak into the managed network and production traffic does not leak into the management network.
Fix Text
If the management interface is not a dedicated OOBM interface, it must be configured with both an ingress and egress ACL. Step 1: Configure an ingress ACL as shown in the example below: SW1(config)#ip access-list extended INGRESS_MANAGEMENT_ACL SW1(config-ext-nacl)#permit tcp any host 10.11.1.22 eq tacacs SW1(config-ext-nacl)#permit tcp any host 10.11.1.22 eq 22 SW1(config-ext-nacl)#permit udp any host 10.11.1.22 eq snmp SW1(config-ext-nacl)#permit udp any host 10.11.1.22 eq snmptrap SW1(config-ext-nacl)#permit udp any host 10.11.1.22 eq ntp SW1(config-ext-nacl)#permit icmp any host 10.11.1.22 SW1(config-ext-nacl)#deny ip any any log-input SW1(config-ext-nacl)#exit Step 2: Configure an egress ACL as shown in the example below: SW1(config)#ip access-list extended EGRESS_MANAGEMENT_ACL SW1(config-ext-nacl)#deny ip any any log-input SW1(config-ext-nacl)#exit Step 3: Apply the ACLs to the OOBM interfaces. SW1(config)#int g0/7 SW1(config-if)#ip access-group INGRESS_MANAGEMENT_ACL in SW1(config-if)#ip access-group EGRESS_MANAGEMENT_ACL out
Check Content
This requirement is only applicable where management access to the switch is via an OOBM interface, which is not a true OOBM interface. Step 1: Verify that the managed interface has an inbound and outbound access control list (ACL) configured. interface GigabitEthernet0/7 no switchport description link to OOBM access switch ip address 10.11.1.22 255.255.255.0 ip access-group INGRESS_MANAGEMENT_ACL in ip access-group EGRESS_MANAGEMENT_ACL in Step 2: Verify that the ingress ACL only allows management and ICMP traffic. ip access-list extended INGRESS_MANAGEMENT_ACL permit tcp any host 10.11.1.22 eq tacacs permit tcp any host 10.11.1.22 eq 22 permit udp any host 10.11.1.22 eq snmp permit udp any host 10.11.1.22 eq snmptrap permit udp any host 10.11.1.22 eq ntp permit icmp any host 10.11.1.22 deny ip any any log-input Step 3: Verify that the egress ACL blocks any transit traffic. ip access-list extended EGRESS_MANAGEMENT_ACL deny ip any any log-input Note: On Cisco switches, local generated packets are not inspected by outgoing interface access lists. Hence, the above configuration would drop any packets not generated by the switch, blocking any transit traffic. If the switch does not restrict traffic that ingresses and egresses the management interface, this is a finding.
The Cisco PE switch providing MPLS Layer 2 Virtual Private Network (L2VPN) services must be configured to authenticate targeted Label Distribution Protocol (LDP) sessions used to exchange virtual circuit (VC) information using a FIPS-approved message authentication code algorithm.
Discussion
LDP provides the signaling required for setting up and tearing down pseudowires (virtual circuits used to transport Layer 2 frames) across an MPLS IP core network. Using a targeted LDP session, each PE switch advertises a virtual circuit label mapping that is used as part of the label stack imposed on the frames by the ingress PE switch during packet forwarding. Authentication provides protection against spoofed TCP segments that can be introduced into the LDP sessions.
Fix Text
The severity level can be downgraded to a CAT III if the switch is configured to authenticate targeted LDP sessions using MD5 as shown in the example below: SW1(config)#mpls ldp neighbor 10.1.1.2 password xxxxxxxx
Check Content
The Cisco switch is not compliant with this requirement; hence, it is a finding. However, the severity level can be downgraded to a CAT III if the switch is configured to authenticate targeted LDP sessions using MD5 as shown in the configuration example below: mpls ldp neighbor 10.1.1.2 password xxxxxxx mpls label protocol ldp If the switch is not configured to authenticate targeted LDP sessions using MD5, the finding will remain as a CAT II.
The Cisco PE switch must be configured to block any traffic that is destined to the IP core infrastructure.
Discussion
IP addresses can be guessed. Core network elements must not be accessible from any external host. Protecting the core from any attack is vital for the integrity and privacy of customer traffic as well as the availability of transit services. A compromise of the IP core can result in an outage or, at a minimum, non-optimized forwarding of customer traffic. Protecting the core from an outside attack also prevents attackers from using the core to attack any customer. Hence, it is imperative that all switches at the edge deny traffic destined to any address belonging to the IP core infrastructure.
Fix Text
Configure protection for the IP core to be implemented at the edges by blocking any traffic with a destination address assigned to the IP core infrastructure. Step 1: Configure an ingress ACL to discard and log packets destined to the IP core address space. SW2(config)#ip access-list extended BLOCK_TO_CORE SW2(config-ext-nacl)#deny ip any 10.1.x.0 0.0.255.255 log-input SW2(config-ext-nacl)#exit Step 2: Apply the ACL inbound to all external or CE-facing interfaces. SW2(config)#int SW1(config)#int g0/2 SW2(config-if)#ip access-group BLOCK_TO_CORE in SW2(config-if)#end
Check Content
Step 1: Review the switch configuration to verify that an ingress ACL is applied to all external or CE-facing interfaces. interface GigabitEthernet0/2 no switchport ip address x.1.12.2 255.255.255.252 ip access-group BLOCK_TO_CORE in Step 2: Verify that the ingress ACL discards and logs packets destined to the IP core address space. ip access-list extended BLOCK_TO_CORE deny ip any 10.1.x.0 0.0.255.255 log-input permit ip any any ! If the PE switch is not configured to block any traffic with a destination address assigned to the IP core infrastructure, this is a finding. Note: Internet Control Message Protocol (ICMP) echo requests and traceroutes will be allowed to the edge from external adjacent neighbors.
The Cisco PE switch must be configured with Unicast Reverse Path Forwarding (uRPF) loose mode enabled on all CE-facing interfaces.
Discussion
The uRPF feature is a defense against spoofing and denial-of-service (DoS) attacks by verifying if the source address of any ingress packet is reachable. To mitigate attacks that rely on forged source addresses, all provider edge switches must enable uRPF loose mode to guarantee that all packets received from a CE switch contain source addresses that are in the route table.
Fix Text
Configure uRPF loose mode on all CE-facing interfaces as shown in the example below: SW2(config)#int SW1(config)#int g0/2 SW2(config-if)#ip verify unicast source reachable-via any SW2(config-if)#end
Check Content
Review the switch configuration to determine if uRPF loose mode is enabled on all CE-facing interfaces. interface GigabitEthernet0/2 no switchport ip address x.1.12.2 255.255.255.252 ip access-group BLOCK_TO_CORE in ip verify unicast source reachable-via any If uRPF loose mode is not enabled on all CE-facing interfaces, this is a finding.
The Cisco PE switch must be configured to ignore or drop all packets with any IP options.
Discussion
Packets with IP options are not fast-switched and therefore must be punted to the switch processor. Hackers who initiate denial-of-service (DoS) attacks on switches commonly send large streams of packets with IP options. Dropping the packets with IP options reduces the load of IP options packets on the switch. The end result is a reduction in the effects of the DoS attack on the switch and on downstream switches.
Fix Text
Configure the switch to ignore or drop all packets with IP options as shown in the examples below: SW1(config)#ip options ignore or SW1(config)#ip options drop
Check Content
Review the switch configuration to determine if it will ignore or drop all packets with IP options as shown in the examples below: ip options drop or ip options ignore If the switch is not configured to drop or block all packets with IP options, this is a finding.
The Cisco PE switch must be configured to enforce a Quality-of-Service (QoS) policy in accordance with the QoS GIG Technical Profile.
Discussion
Different applications have unique requirements and toleration levels for delay, jitter, bandwidth, packet loss, and availability. To manage the multitude of applications and services, a network requires a QoS framework to differentiate traffic and provide a method to manage network congestion. The Differentiated Services Model (DiffServ) is based on per-hop behavior by categorizing traffic into different classes and enabling each node to enforce a forwarding treatment to each packet as dictated by a policy. Packet markings such as IP Precedence and its successor, Differentiated Services Code Points (DSCP), were defined along with specific per-hop behaviors for key traffic types to enable a scalable QoS solution. DiffServ QoS categorizes network traffic, prioritizes it according to its relative importance, and provides priority treatment based on the classification. It is imperative that end-to-end QoS is implemented within the IP core network to provide preferred treatment for mission-critical applications.
Fix Text
Configure a QoS policy in accordance with the QoS GIG Technical Profile. Step 1: Configure class-maps to match on DSCP values as shown in the configuration example below: SW1(config)#class-map match-all PREFERRED_DATA SW1(config-cmap)#match ip dscp af33 SW1(config-cmap)#class-map match-all CONTROL_PLANE SW1(config-cmap)#match ip dscp cs6 SW1(config-cmap)#class-map match-all VIDEO SW1(config-cmap)#match ip dscp af41 SW1(config-cmap)#class-map match-all VOICE SW1(config-cmap)#match ip dscp ef SW1(config-cmap)#class-map match-all C2_VOICE SW1(config-cmap)#match ip dscp 47 SW1(config-cmap)#exit Step 2: Configure a policy map to be applied to the core-layer-facing interface that reserves the bandwidth for each traffic type as shown in the example below: SW1(config)#policy-map QOS_POLICY SW1(config-pmap)#class CONTROL_PLANE SW1(config-pmap-c)#priority percent 10 SW1(config-pmap-c)#class C2_VOICE SW1(config-pmap-c)#priority percent 10 SW1(config-pmap-c)#class VOICE SW1(config-pmap-c)#priority percent 15 SW1(config-pmap-c)#class VIDEO SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class PREFERRED_DATA SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class class-default SW1(config-pmap-c)#bandwidth percent 15 SW1(config-pmap-c)#exit SW1(config-pmap)#exit Step 3: Apply the output service policy to all interfaces as shown in the configuration example below: SW1(config)#int g1/1 SW1(config-if)#service-policy output QOS_POLICY SW1(config-if)#exit SW1(config)#int g1/2 SW1(config-if)#service-policy output QOS_POLICY SW1(config-if)#end
Check Content
Review the switch configuration and verify that a QoS policy has been configured to provide preferred treatment for mission-critical applications in accordance with the QoS GIG Technical Profile. Step 1: Verify that the class-maps are configured to match on DSCP values as shown in the configuration example below: class-map match-all C2_VOICE match ip dscp af47 class-map match-all VOICE match ip dscp ef class-map match-all VIDEO match ip dscp af41 class-map match-all CONTROL_PLANE match ip dscp cs6 class-map match-all PREFERRED_DATA match ip dscp af33 Step 2: Verify that the policy map reserves the bandwidth for each traffic type as shown in the example below: policy-map QOS_POLICY class C2_VOICE priority percent 10 class VOICE priority percent 15 class VIDEO bandwidth percent 25 class CONTROL_PLANE priority percent 10 class PREFERRED_DATA bandwidth percent 25 class class-default bandwidth percent 15 Step 3: Verify that an output service policy is bound to all interfaces as shown in the configuration example below: interface GigabitEthernet1/1 no switchport ip address 10.1.15.1 255.255.255.252 service-policy output QOS_POLICY ! interface GigabitEthernet1/2 no switchport ip address 10.1.15.4 255.255.255.252 service-policy output QOS_POLICY Note: Enclaves must mark or re-mark their traffic to be consistent with the DODIN backbone admission criteria to gain the appropriate level of service. A general DiffServ principle is to mark or trust traffic as close to the source as administratively and technically possible. However, certain traffic types might need to be re-marked before handoff to the DODIN backbone to gain admission to the correct class. If such re-marking is required, it is recommended that the re-marking be performed at the CE egress edge. Note: The GTP QOS document (GTP-0009) can be downloaded via the following link: https://intellipedia.intelink.gov/wiki/Portal:GIG_Technical_Guidance/GTG_GTPs/GTP_Development_List If the switch is not configured to enforce a QoS policy in accordance with the QoS GIG Technical Profile, this is a finding.
The Cisco P switch must be configured to implement a Quality-of-Service (QoS) policy in accordance with the QoS GIG Technical Profile.
Discussion
Different applications have unique requirements and toleration levels for delay, jitter, bandwidth, packet loss, and availability. To manage the multitude of applications and services, a network requires a QoS framework to differentiate traffic and provide a method to manage network congestion. The Differentiated Services Model (DiffServ) is based on per-hop behavior by categorizing traffic into different classes and enabling each node to enforce a forwarding treatment to each packet as dictated by a policy. Packet markings such as IP Precedence and its successor, Differentiated Services Code Points (DSCP), were defined along with specific per-hop behaviors for key traffic types to enable a scalable QoS solution. DiffServ QoS categorizes network traffic, prioritizes it according to its relative importance, and provides priority treatment based on the classification. It is imperative that end-to-end QoS is implemented within the IP core network to provide preferred treatment for mission-critical applications.
Fix Text
Configure a QoS policy in accordance with the QoS GIG Technical Profile. Step 1: Configure class-maps to match on DSCP values as shown in the configuration example below: SW1(config)#class-map match-all PREFERRED_DATA SW1(config-cmap)#match ip dscp af33 SW1(config-cmap)#class-map match-all CONTROL_PLANE SW1(config-cmap)#match ip dscp cs6 SW1(config-cmap)#class-map match-all VIDEO SW1(config-cmap)#match ip dscp af41 SW1(config-cmap)#class-map match-all VOICE SW1(config-cmap)#match ip dscp ef SW1(config-cmap)#class-map match-all C2_VOICE SW1(config-cmap)#match ip dscp 47 SW1(config-cmap)#exit Step 2: Configure a policy map to be applied to the core-layer-facing interface that reserves the bandwidth for each traffic type as shown in the example below: SW1(config)#policy-map QOS_POLICY SW1(config-pmap)#class CONTROL_PLANE SW1(config-pmap-c)#priority percent 10 SW1(config-pmap-c)#class C2_VOICE SW1(config-pmap-c)#priority percent 10 SW1(config-pmap-c)#class VOICE SW1(config-pmap-c)#priority percent 15 SW1(config-pmap-c)#class VIDEO SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class PREFERRED_DATA SW1(config-pmap-c)#bandwidth percent 25 SW1(config-pmap-c)#class class-default SW1(config-pmap-c)#bandwidth percent 15 SW1(config-pmap-c)#exit SW1(config-pmap)#exit Step 3: Apply the output service policy to all interfaces as shown in the configuration example below: SW1(config)#int g1/1 SW1(config-if)#service-policy output QOS_POLICY SW1(config-if)#exit SW1(config)#int g1/2 SW1(config-if)#service-policy output QOS_POLICY SW1(config-if)#end
Check Content
Review the switch configuration and verify that a QoS policy has been configured to provide preferred treatment for mission-critical applications in accordance with the QoS GIG Technical Profile. Step 1: Verify that the class-maps are configured to match on DSCP values as shown in the configuration example below: class-map match-all PREFERRED_DATA match ip dscp af33 class-map match-all CONTROL_PLANE match ip dscp cs6 class-map match-all VIDEO match ip dscp af41 class-map match-all VOICE match ip dscp ef class-map match-all C2_VOICE match ip dscp 47 Step 2: Verify that the policy map reserves the bandwidth for each traffic type as shown in the example below: policy-map QOS_POLICY class CONTROL_PLANE priority percent 10 class C2_VOICE priority percent 10 class VOICE priority percent 15 class VIDEO bandwidth percent 25 class PREFERRED_DATA bandwidth percent 25 class class-default bandwidth percent 15 Step 3: Verify that an output service policy is bound to all interfaces as shown in the configuration example below: interface GigabitEthernet1/1 no switchport ip address 10.1.15.5 255.255.255.252 service-policy output QOS_POLICY ! interface GigabitEthernet1/2 no switchport ip address 10.1.15.8 255.255.255.252 service-policy output QOS_POLICY Note: The GTP QOS document (GTP-0009) can be downloaded via the following link: https://intellipedia.intelink.gov/wiki/Portal:GIG_Technical_Guidance/GTG_GTPs/GTP_Development_List If the switch is not configured to enforce a QoS policy in accordance with the QoS GIG Technical Profile, this is a finding.
The Cisco switch must be configured to enforce a Quality-of-Service (QoS) policy to limit the effects of packet flooding denial-of-service (DoS) attacks.
Discussion
DoS is a condition when a resource is not available for legitimate users. Packet flooding distributed denial-of-service (DDoS) attacks are referred to as volumetric attacks and have the objective of overloading a network or circuit to deny or seriously degrade performance, which denies access to the services that normally traverse the network or circuit. Volumetric attacks have become relatively easy to launch using readily available tools such as Low Orbit Ion Cannon or botnets. Measures to mitigate the effects of a successful volumetric attack must be taken to ensure that sufficient capacity is available for mission-critical traffic. Managing capacity may include, for example, establishing selected network usage priorities or quotas and enforcing them using rate limiting, Quality of Service (QoS), or other resource reservation control methods. These measures may also mitigate the effects of sudden decreases in network capacity that are the result of accidental or intentional physical damage to telecommunications facilities (such as cable cuts or weather-related outages).
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Step 1: Configure a class-map for the SCAVENGER class. SW1(config)#class-map match-all SCAVENGER SW1(config-cmap)#match ip dscp cs1 Step 2: Add the SCAVENGER class to the policy-map as shown in the example below: SW1(config)#policy-map QOS_POLICY SW1(config-pmap-c)#no class class-default SW1(config-pmap)#class SCAVENGER SW1(config-pmap-c)#bandwidth percent 5 SW1(config-pmap-c)#class class-default SW1(config-pmap-c)#bandwidth percent 10 SW1(config-pmap-c)#end
Check Content
Review the switch configuration to determine if it is configured to enforce a QoS policy to limit the effects of packet flooding DoS attacks. Step 1: Verify that a class-map has been configured for the Scavenger class as shown in the example below: class-map match-all SCAVENGER match ip dscp cs1 Step 2: Verify that the policy-map includes the SCAVENGER class with low priority as shown in the example below: policy-map QOS_POLICY class CONTROL_PLANE priority percent 10 class C2_VOICE priority percent 10 class VOICE priority percent 15 class VIDEO bandwidth percent 25 class PREFERRED_DATA bandwidth percent 25 class SCAVENGER bandwidth percent 5 class class-default bandwidth percent 10 Note: Traffic out of profile must be marked at the customer access layer or CE egress edge. If the switch is not configured to enforce a QoS policy to limit the effects of packet flooding DoS attacks, this is a finding.
The Cisco multicast switch must be configured to disable Protocol Independent Multicast (PIM) on all interfaces that are not required to support multicast routing.
Discussion
If multicast traffic is forwarded beyond the intended boundary, it is possible that it can be intercepted by unauthorized or unintended personnel. Limiting where, within the network, a given multicast group's data is permitted to flow is an important first step in improving multicast security. A scope zone is an instance of a connected region of a given scope. Zones of the same scope cannot overlap, while zones of a smaller scope will fit completely within a zone of a larger scope. For example, Admin-local scope is smaller than Site-local scope, so the administratively configured boundary fits within the bounds of a site. According to RFC 4007 IPv6 Scoped Address Architecture (section 5), scope zones are also required to be "convex from a routing perspective"; that is, packets routed within a zone must not pass through any links that are outside of the zone. This requirement forces each zone to be one contiguous island rather than a series of separate islands. As stated in the DoD IPv6 IA Guidance for MO3, "One should be able to identify all interfaces of a zone by drawing a closed loop on their network diagram, engulfing some switches and passing through some switches to include only some of their interfaces." Therefore, it is imperative that the network engineers have documented their multicast topology and know which interfaces are enabled for multicast. Once this is done, the zones can be scoped as required.
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Document all enabled interfaces for PIM in the network's multicast topology diagram. Disable support for PIM on interfaces that are not required to support it. SW1(config)#int g1/1 SW1(config-if)#no ip pim sparse-mode
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Step 1: Review the network's multicast topology diagram. Step 2: Review the switch configuration to verify that only the PIM interfaces as shown in the multicast topology diagram are enabled for PIM as shown in the example below: interface GigabitEthernet1/1 no switchport ip address 10.1.3.3 255.255.255.0 ip pim sparse-mode If an interface is not required to support multicast routing and it is enabled, this is a finding.
The Cisco multicast switch must be configured to bind a Protocol Independent Multicast (PIM) neighbor filter to interfaces that have PIM enabled.
Discussion
PIM is a routing protocol used to build multicast distribution trees for forwarding multicast traffic across the network infrastructure. PIM traffic must be limited to only known PIM neighbors by configuring and binding a PIM neighbor filter to interfaces that have PIM enabled. If a PIM neighbor filter is not applied to interfaces that have PIM enabled, unauthorized switches can join the PIM domain, discover and use the rendezvous points, and advertise their rendezvous points into the domain. This can result in a denial of service by traffic flooding or in the unauthorized transfer of data.
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Configure neighbor ACLs to only accept PIM control plane traffic from documented PIM neighbors. Bind neighbor ACLs to all PIM-enabled interfaces. Step 1: Configure ACL for PIM neighbors. SW2(config)#ip access-list standard PIM_NEIGHBORS SW2(config-std-nacl)#permit 10.1.2.6 SW2(config-std-nacl)#exit Step 2: Apply the ACL to all interfaces enabled for PIM. SW2(config)#int g1/1 SW2(config-if)#ip pim neighbor-filter PIM_NEIGHBORS
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Step 1: Verify that all interfaces enabled for PIM have a neighbor access control list (ACL) bound to the interface as shown in the example below: interface GigabitEthernet1/1 no switchport ip address 10.1.2.2 255.255.255.0 ip pim neighbor-filter PIM_NEIGHBORS ip pim sparse-mode Step 2: Review the configured ACL for filtering PIM neighbors as shown in the example below: ip access-list standard PIM_NEIGHBORS permit 10.1.2.6 If PIM neighbor ACLs are not bound to all interfaces that have PIM enabled, this is a finding.
The Cisco multicast edge switch must be configured to establish boundaries for administratively scoped multicast traffic.
Discussion
If multicast traffic is forwarded beyond the intended boundary, it is possible that it can be intercepted by unauthorized or unintended personnel. Administrative scoped multicast addresses are locally assigned and are to be used exclusively by the enterprise network or enclave. Administrative scoped multicast traffic must not cross the enclave perimeter in either direction. Restricting multicast traffic makes it more difficult for a malicious user to access sensitive traffic. Admin-Local scope is encouraged for any multicast traffic within a network intended for network management, as well as for control plane traffic that must reach beyond link-local destinations.
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Step 1: Configure the ACL to deny packets with multicast administratively scoped destination addresses as shown in the example below: SW2(config)#ip access-list standard MULTICAST_SCOPE SW2(config-std-nacl)#deny 239.0.0.0 0.255.255.255 SW2(config-std-nacl)#permit any SW2(config-std-nacl)#exit Step 2: Apply the multicast boundary at the appropriate interfaces as shown in the example below: SW2(config)#int g1/2 SW2(config-if)#ip multicast boundary MULTICAST_SCOPE SW2(config-if)#end
Check Content
Review the switch configuration and verify that admin-scope multicast traffic is blocked at the external edge as shown in the example below: interface GigabitEthernet1/2 no switchport ip address x.1.12.2 255.255.255.252 ip pim sparse-mode ip multicast boundary MULTICAST_SCOPE … … … ip access-list standard MULTICAST_SCOPE deny 239.0.0.0 0.255.255.255 permit any If the switch is not configured to establish boundaries for administratively scoped multicast traffic, this is a finding.
The Cisco multicast Designated switch (DR) must be configured to filter the Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Report messages to allow hosts to join only multicast groups that have been approved by the organization.
Discussion
Real-time multicast traffic can entail multiple large flows of data. Large unicast flows tend to be fairly isolated (i.e., someone doing a file download here or there), whereas multicast can have broader impact on bandwidth consumption, resulting in extreme network congestion. Hence, it is imperative that there is multicast admission control to restrict which multicast group's hosts are allowed to join via IGMP or MLD.
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Configure the DR to filter the IGMP or MLD Membership Report messages to allow hosts to join only multicast groups that have been approved. Step 1: Configure the ACL to filter IGMP Membership Report messages as shown in the example below: SW2(config)#ip access-list standard IGMP_JOIN_FILTER SW2(config-std-nacl)#deny 239.8.0.0 0.0.255.255 SW2(config-std-nacl)#permit any SW2(config-std-nacl)#exit Step 2: Apply the filter to all host-facing Layer 3 and VLAN interfaces. SW2(config)#int vlan3 SW2(config-if)#ip igmp access-group IGMP_JOIN_FILTER
Check Content
Review the configuration of the DR to verify that it is filtering IGMP or MLD Membership Report messages, allowing hosts to join only groups that have been approved. Step 1: Verify that all host-facing Layer 3 and VLAN interfaces are configured to filter IGMP Membership Report messages (IGMP joins) as shown in the example below: interface Vlan3 ip address 10.3.3.3 255.255.255.0 ip pim sparse-mode ip igmp access-group IGMP_JOIN_FILTER ip igmp version 3 Step 2: Verify that the ACL denies unauthorized groups or permits only authorized groups. The example below denies all groups from 239.8.0.0/16 range. ip access-list standard IGMP_JOIN_FILTER deny 239.8.0.0 0.0.255.255 permit any Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. This requirement is not applicable to Any Source Multicast (ASM) since the filtering is being performed by the Rendezvous Point switch. If the DR is not filtering IGMP or MLD Membership Report messages, this is a finding.
The Cisco multicast Designated switch (DR) must be configured to limit the number of mroute states resulting from Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Host Membership Reports.
Discussion
The current multicast paradigm can let any host join any multicast group at any time by sending an IGMP or MLD membership report to the DR. In a Protocol Independent Multicast (PIM) Sparse Mode network, the DR will send a PIM Join message for the group to the RP. Without any form of admission control, this can pose a security risk to the entire multicast domain, specifically the multicast switches along the shared tree from the DR to the RP that must maintain the mroute state information for each group join request. Hence, it is imperative that the DR is configured to limit the number of mroute state information that must be maintained to mitigate the risk of IGMP or MLD flooding.
Fix Text
Configure the DR on a global or interface basis to limit the number of mroute states resulting from IGMP or MLD membership reports. SW2(config)#int vlan3 SW2(config-if)#ip igmp limit 2
Check Content
Review the DR configuration to verify that it is limiting the number of mroute states via IGMP or MLD. Verify IGMP limits have been configured globally or on each host-facing Layer 3 and VLAN interface via the ip igmp limit command as shown in the example below: interface Vlan3 ip address 10.3.3.3 255.255.255.0 … … … ip igmp limit nn If the DR is not limiting multicast join requests via IGMP or MLD on a global or interfaces basis, this is a finding.
The Cisco multicast Designated switch (DR) must be configured to set the shortest-path tree (SPT) threshold to infinity to minimalize source-group (S, G) state within the multicast topology where Any Source Multicast (ASM) is deployed.
Discussion
ASM can have many sources for the same groups (many-to-many). For many receivers, the path via the RP may not be ideal compared with the shortest path from the source to the receiver. By default, the last-hop switch will initiate a switch from the shared tree to a source-specific SPT to obtain lower latencies. This is accomplished by the last-hop switch sending an (S, G) Protocol Independent Multicast (PIM) Join toward S (the source). When the last-hop switch begins to receive traffic for the group from the source via the SPT, it will send a PIM Prune message to the RP for the (S, G). The RP will then send a Prune message toward the source. The SPT switchover becomes a scaling issue for large multicast topologies that have many receivers and many sources for many groups because (S, G) entries require more memory than (*, G). Hence, it is imperative to minimize the amount of (S, G) state to be maintained by increasing the threshold that determines when the SPT switchover occurs.
Fix Text
Configure the DR to increase the SPT threshold or set it to infinity to minimalize (S, G) state within the multicast topology where ASM is deployed. SW2(config)#ip pim spt-threshold infinity
Check Content
Review the DR configuration to verify that the SPT switchover threshold is increased (default is "0") or set to infinity (never switch over). ip pim rp-address 10.2.2.2 ip pim spt-threshold infinity If the DR is not configured to increase the SPT threshold or set to infinity to minimalize (S, G) state, this is a finding.
The Cisco multicast Designated switch (DR) must be configured to filter the Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Report messages to allow hosts to join a multicast group only from sources that have been approved by the organization.
Discussion
Real-time multicast traffic can entail multiple large flows of data. Large unicast flows tend to be fairly isolated (i.e., someone doing a file download here or there), whereas multicast can have broader impact on bandwidth consumption, resulting in extreme network congestion. Hence, it is imperative that there is multicast admission control to restrict which multicast groups hosts are allowed to join via IGMP or MLD.
Fix Text
Configure the DR to filter the IGMP and MLD report messages to allow hosts to join only multicast groups from sources that have been approved as shown in the example below: SW2(config)#ip access-list extended IGMP_JOIN_FILTER SW2(config-ext-nacl)#deny ip any 232.8.0.0 0.0.255.255 SW2(config-ext-nacl)#permit ip x.0.0.0 0.255.255.255 any SW2(config-ext-nacl)#deny ip any any SW2(config-ext-nacl)#exit Step 2: Apply the filter to all host-facing Layer 3 and VLAN interfaces. SW2(config)#int vlan3 SW2(config-if)#ip igmp access-group IGMP_JOIN_FILTER
Check Content
Review the configuration of the DR to verify that it is filtering IGMP or MLD report messages, allowing hosts to only join multicast groups from sources that have been approved. Step 1: Verify that all host-facing Layer 3 and VLAN interfaces are configured to filter IGMP Membership Report messages (IGMP joins) as shown in the example below: interface Vlan3 ip address 10.3.3.3 255.255.255.0 ip pim sparse-mode ip igmp access-group IGMP_JOIN_FILTER ip igmp version 3 Step 2: Verify that the ACL denies unauthorized sources or allows only authorized sources. The example below denies all groups from the 232.8.0.0/16 range and permits sources only from the x.0.0.0/8 network. ip access-list extended IGMP_JOIN_FILTER deny ip any 232.8.0.0 0.0.255.255 permit ip x.0.0.0 0.255.255.255 any deny ip any any Note: This requirement is only applicable to Source Specific Multicast (SSM) implementation. If the DR is not filtering IGMP or MLD report messages, this is a finding.