Title

The perimeter router must be configured to filter egress traffic at the internal interface on an inbound direction. (Cat II impact)

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 routers makes use of access lists for restricting access to services on the router itself as well as for filtering traffic passing through the router. Inbound versus Outbound: It should be noted that 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 router can protect itself before damage is inflicted. - The input port is still known and can be filtered upon. - It is more efficient to filter packets before routing them.

Check Content

This requirement is not applicable for the DoDIN Backbone. Review the router configuration to verify that the egress ACL is bound to the internal interface in an inbound direction. If the router is not configured to filter traffic leaving the network at the internal interface in an inbound direction, this is a finding.

Fix Text

This requirement is not applicable for the DoDIN Backbone. Configure an egress ACL bound to the internal interface in an inbound direction to filter traffic leaving the network.

Additional Identifiers

Rule ID: SV-207137r604135_rule

Vulnerability ID: V-207137

Group Title: SRG-NET-000205

Expert Comments

CCIs tied to check.

Controls tied to check. These are derived from the CCIs shown above.