Information
As a best practice, a service provider should only accept customer prefixes that have been assigned to that customer and any peering autonomous systems. A multi-homed customer with BGP speaking routers connected to the internet or other external networks could be breached and used to launch a prefix de-aggregation attack. Without ingress route filtering of customers, the effectiveness of such an attack could impact the entire IP core and its customers.
NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.
Solution
Step 1: Configure Arista eBGP routers to reject inbound route advertisements from a CE router for prefixes that are not allocated to that specific customer.
LEAF-1A(config)#ip access-list BGP_Enclave_Gateway_Filter_IN
LEAF-1A(config-acl-BGP_Enclave_Gateway_Filter_IN)# 10 permit ip 172.16.50.0/30 any
LEAF-1A(config-acl-BGP_Enclave_Gateway_Filter_IN)# 20 permit ip 10.1.1.0/24 any
LEAF-1A(config-acl-BGP_Enclave_Gateway_Filter_IN)# 30 permit ip 12.15.4.9/32 any
LEAF-1A(config-acl-BGP_Enclave_Gateway_Filter_IN)# 40 deny ip any any log
Step 2: Configure a route-map to match the ACL.
LEAF-1A(config-ip-pfx)#route-map FILTER_INBOUND permit 10
LEAF-1A(config-route-map-FILTER_INBOUND)#match ip address access-list BGP_Enclave_Gateway_Filter_IN
Step 3: Configure the route-map to be applied inbound to the appropriate CE customer neighbor.
LEAF-1A(config)#router bgp 65001
LEAF-1A(config-router-bgp)#neighbor 100.2.1.1 route-map FILTER_INBOUND in