Information
IP/MPLS networks providing VPN and transit services must provide, at the least, the same level of protection against denial-of-service (DoS) attacks and intrusions as Layer 2 networks. Although the IP core network elements are hidden, security should never rely entirely on obscurity.
IP addresses can be guessed. Core network elements must not be accessible from any external host. Protecting the core from any attack is vital for the integrity and privacy of customer traffic as well as the availability of transit services. A compromise of the IP core can result in an outage or, at a minimum, non-optimized forwarding of customer traffic. Protecting the core from an outside attack also prevents attackers from using the core to attack any customer. Hence, it is imperative that all routers at the edge deny traffic destined to any address belonging to the IP core infrastructure.
NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.
Solution
Configure protection for the IP core to be implemented at the edges by blocking any traffic with a destination address assigned to the IP core infrastructure.
Step 1: Configure an ingress ACL to drop any traffic with destination address assigned to the IP core infrastructure.
router(config)#ip access-list DROP_INBOUND
router(config-acl-DROP_INBOUND)#deny ip any 172.16.0.0/16 log
router(config-acl-DROP_INBOUND)#permit icmp any any
router(config-acl-DROP_INBOUND)#permit ip any any
router(config-acl-DROP_INBOUND)#exit
Step 2: Apply the ACL to all CE-facing interfaces inbound to drop all the traffic coming toward the CE.
router(config)#interface Ethernet 2
router(config-if-Et2)#ip access-group DROP_INBOUND in
router(config-if-Et2)#end