Information
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.
Satisfies: SRG-NET-000205-RTR-000003, SRG-NET-000205-RTR-000004
NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.
Solution
This requirement is not applicable for the DODIN backbone.
Bind the ingress ACL to the external interface (inbound).
Step 1: Configure the ACL.
LEAF-1A(config)#ip access-list INBOUND
LEAF-1A(config-acl-INBOUND)#10 permit tcp 10.10.10.0/24 host 10.20.10.1 eq ssh telnet
LEAF-1A(config-acl-INBOUND)#20 permit ip 10.10.10.0/24 192.168.10.0/24
LEAF-1A(config-acl-INBOUND)#30 permit udp 10.20.20.0/24 any eq bootps snmp
LEAF-1A(config-acl-INBOUND)#40 deny ip any any log
Step 2: Apply the ACL inbound on all external interfaces.
LEAF-1A(config)#interface ethernet 13
LEAF-1A(config-if-Et13)#ip access-group INBOUND in