The Cisco perimeter router must be configured to filter ingress traffic at the external interface on an inbound direction.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-216671	CISC-RT-000330	SV-216671r531086_rule		Medium

Description
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.

Description

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.

STIG	Date
Cisco IOS XE Router RTR Security Technical Implementation Guide	2021-03-26

Details

Check Text ( C-17904r287967_chk )
This requirement is not applicable for the DODIN Backbone. Review the router 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 router is not configured to filter traffic entering the network at all external interfaces in an inbound direction, this is a finding.

Check Text ( C-17904r287967_chk )

This requirement is not applicable for the DODIN Backbone.

Review the router 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 router is not configured to filter traffic entering the network at all external interfaces in an inbound direction, this is a finding.

Fix Text (F-17902r287968_fix)
This requirement is not applicable for the DODIN Backbone. Configure the router to use an inbound ACL on all external interfaces as shown in the example below: R1(config)#int g0/2 R1(config-if)#ip access-group EXTERNAL_ACL_INBOUND in