The Cisco perimeter switch must be configured to have Link Layer Discovery Protocol (LLDP) disabled on all external interfaces.
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.
Disable LLDP transmit on all external interfaces as shown in the example below: SW1(config)#int g0/1 SW1(config-if)#no lldp transmit
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.