V-216711

Discussion

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.

Check Content

Step 1: Review the router configuration to verify that an ingress ACL is applied to all external or CE-facing interfaces. 

interface GigabitEthernet0/2
 ip address x.1.12.2 255.255.255.252
 ip access-group BLOCK_TO_CORE in

Step 2: Verify that the ingress ACL discards and logs packets destined to the IP core address space. 

ip access-list extended BLOCK_TO_CORE
 deny   ip any 10.1.x.0 0.0.255.255 log-input
 permit ip any any
!

If the PE router is not configured to block any traffic with a destination address assigned to the IP core infrastructure, this is a finding.

Note: Internet Control Message Protocol (ICMP) echo requests and traceroutes will be allowed to the edge from external adjacent neighbors.