V-220445

Discussion

Vulnerability assessments must be reviewed by the System Administrator, and protocols must be approved by the Information Assurance (IA) staff before entering the enclave. Access control lists (ACLs) are the first line of defense in a layered security approach. They permit authorized packets and deny unauthorized packets based on port or service type. They enhance the posture of the network by not allowing packets to reach a potential target within the security domain. The lists provided are highly susceptible ports and services that should be blocked or limited as much as possible without adversely affecting customer requirements. Auditing packets attempting to penetrate the network that are stopped by an ACL will allow network administrators to broaden their protective ring and more tightly define the scope of operation. If the perimeter is in a Deny-by-Default posture and what is allowed through the filter is in accordance with DoD Instruction 8551.1, and if the permit rule is explicitly defined with explicit ports and protocols allowed, then all requirements related to PPS being blocked would be satisfied.

Check Content

Review the switch configuration to verify that the ingress ACL is in accordance with DoD 8551.1. 

Step 1: Verify that an inbound ACL is configured on all external interfaces. 

interface GigabitEthernet0/2 
 ip address x.11.1.2 255.255.255.254 
 ip access-group EXTERNAL_ACL_INBOUND in 

Step 2. Review the inbound ACL to verify that it is filtering traffic in accordance with DoD 8551.1. 

ip access-list extended EXTERNAL_ACL_INBOUND 
 permit tcp any any established 
 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 
… 
 … < must be in accordance with DoD Instruction 8551.1> 
… 
deny ip any any log-input 

If the switch does not filter traffic in accordance with the guidelines contained in DoD 8551.1, this is a finding.