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V-74107

The Cisco IOS XE router must protect an enclave connected to an Alternate Gateway by using an inbound filter that only permits packets with destination addresses within the sites address space.

Finding ID
CISR-RT-000006
Rule ID
SV-88781r2_rule
Severity
Cat I
CCE
(None)
Group Title
SRG-NET-000019-RTR-000009
CCI
CCI-001414
Target Key
(None)
Documentable
No
Discussion

Enclaves with Alternate Gateway connections must take additional steps to ensure there is no compromise on the enclave network or NIPRNet. Without verifying the destination address of traffic coming from the site's Alternate Gateway, the perimeter router could be routing transit data from the Internet into the NIPRNet. This could also make the perimeter router vulnerable to a DoS attack as well as provide a backdoor into the NIPRNet. The DoD enclave must ensure the ingress filter applied to external interfaces on a perimeter router connecting to an Approved Gateway is secure through filters permitting packets with a destination address belonging to the DoD enclave's address block.

Fix Text

Configure the Cisco IOS XE router to permit packets with destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the Alternate Gateway network service provider. The configuration would look similar to the example below: interface GigabitEthernet 0/0/1 description Alternate Gateway link ip address x.x.x.x 255.255.255.0 ip access-group Alternate_Gateway_ACL in ... ip access-list extended Alternate_Gateway_ACL permit ip 1.1.1.0 0.0.0.255 any log ...

Check Content

Review the configuration of each router interface connecting to an Alternate Gateway on the Cisco IOS XE router. Verify each permit statement of the ingress filter only permits packets with destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the Alternate Gateway network service provider. If the ingress filter permits packets with addresses other than those specified, such as destination addresses of the site's NIPRNet address space or a destination address belonging to the address block assigned by the Alternate Gateway network service provider, this is a finding.