STIGQter: STIG Summary: Cisco IOS XE Router RTR Security Technical Implementation Guide Version: 2 Release: 2 Benchmark Date: 23 Apr 2021:

The Cisco perimeter router must be configured to deny network traffic by default and allow network traffic by exception.

DISA Rule

SV-216662r531086_rule

Vulnerability Number

V-216662

Group Title

SRG-NET-000202-RTR-000001

Rule Version

CISC-RT-000240

Severity

CAT I

CCI(s)

• CCI-001109 - The information system at managed interfaces denies network communications traffic by default and allows network communications traffic by exception (i.e., deny all, permit by exception).

Weight

10

Fix Recommendation

This requirement is not applicable for the DODIN Backbone.

Step 1: Configure an inbound ACL to deny all other traffic by default as shown in the example below:

R1(config)#ip access-list extended EXTERNAL_ACL
R1(config-ext-nacl)#permit tcp any any established
R1(config-ext-nacl)#permit tcp host x.11.1.1 eq bgp host x.11.1.2
R1(config-ext-nacl)#permit tcp host x.11.1.1 host x.11.1.2 eq bgp
R1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo
R1(config-ext-nacl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply
…
…
…
R1(config-ext-nacl)#deny ip any any log-input

Step 2: Apply the ingress filter to all external interfaces.

R1(config)#int g0/2
R1(config-if)#ip access-group EXTERNAL_ACL in

Check Contents

This requirement is not applicable for the DODIN Backbone.

Review the router configuration to verify that the inbound 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 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 tcp host x.11.1.1 eq bgp host x.11.1.2
permit tcp host x.11.1.1 host x.11.1.2 eq bgp
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.

Vulnerability Number

V-216662

Documentable

False

Rule Version

CISC-RT-000240

Severity Override Guidance

This requirement is not applicable for the DODIN Backbone.

Review the router configuration to verify that the inbound 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 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 tcp host x.11.1.1 eq bgp host x.11.1.2
permit tcp host x.11.1.1 host x.11.1.2 eq bgp
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.

Check Content Reference

M

Target Key

4028

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