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The Cisco perimeter router must be configured to deny network traffic by default and allow network traffic by exception.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
|---|---|---|---|---|
| V-216752 | CISC-RT-000240 | SV-216752r531087_rule | High |
| Description |
|---|
| A deny-all, permit-by-exception network communications traffic policy ensures that only connections that are essential and approved are allowed. This requirement applies to both inbound and outbound network communications traffic. All inbound and outbound traffic must be denied by default. Firewalls and perimeter routers should only allow traffic through that is explicitly permitted. The initial defense for the internal network is to block any traffic at the perimeter that is attempting to make a connection to a host residing on the internal network. In addition, allowing unknown or undesirable outbound traffic by the firewall or router will establish a state that will permit the return of this undesirable traffic inbound. |
| STIG | Date |
|---|---|
| Cisco IOS XR Router RTR Security Technical Implementation Guide | 2024-06-06 |
Details
| Check Text ( C-17984r288645_chk ) |
|---|
| 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 GigabitEthernet0/0/0/1 ipv4 address x.11.1.2 255.255.255.252 ipv4 access-group EXTERNAL_ACL_INBOUND ingress Step 2: Review inbound ACL to verify that it is configured to deny all other traffic that is not explicitly allowed. ipv4 access-list EXTERNAL_ACL_INBOUND 10 permit tcp host x.11.1.1 eq bgp host x.11.1.2 20 permit tcp host x.11.1.1 host x.11.1.2 eq bgp 30 permit icmp host x.11.1.1 host x.11.1.2 echo 40 permit icmp host x.11.1.1 host x.11.1.2 echo-reply 50 deny ipv4 any host x.11.1.1 log-input 60 permit tcp any any established … … … 140 deny ipv4 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. |
| Fix Text (F-17982r288646_fix) |
|---|
| 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. RP/0/0/CPU0:R3(config)#ipv4 access-list EXTERNAL_ACL_INBOUND RP/0/0/CPU0:R3(config-ipv4-acl)#permit tcp host x.11.1.1 eq bgp host x.11.1.2 RP/0/0/CPU0:R3(config-ipv4-acl)#permit tcp host x.11.1.1 host x.11.1.2 eq bgp RP/0/0/CPU0:R3(config-ipv4-acl)#permit icmp host x.11.1.1 host x.11.1.2 echo RP/0/0/CPU0:R3(config-ipv4-acl)#permit icmp host x.11.1.1 host x.11.1.2 echo-reply RP/0/0/CPU0:R3(config-ipv4-acl)#deny ip any host x.11.1.1 log-input RP/0/0/CPU0:R3(config-ipv4-acl)#permit tcp any any established … … … RP/0/0/CPU0:R3(config-ipv4-acl)#deny ip any any log-input RP/0/0/CPU0:R3(config-ipv4-acl)#exit Step 2: Apply the ingress filter to all external interfaces RP/0/0/CPU0:R3(config)#int g0/0/0/1 RP/0/0/CPU0:R3(config-if)#ipv4 access-group EXTERNAL_ACL_INBOUND in RP/0/0/CPU0:R3(config-if)#end |