V-255989

Discussion

Accepting route advertisements belonging to the local AS can result in traffic looping or being black holed, or at a minimum using a non-optimized path.

Check Content

Review the Arista router configuration to verify that it will reject routes belonging to the local AS.

The prefix filter must be referenced inbound on the appropriate BGP neighbor statements.

Step 1: Review the prefix lists configured on the router to filter the local AS prefix (10.12.0.0/16). To verify IP prefix lists are configured, execute the command "show ip prefix-list".

router#sh ip prefix-list
router#ip prefix-list LOCAL_SCOPE_BOUNDARY
   seq 10 deny 10.12.0.0/16
   seq  100 permit  0.0.0.0/0 le32

Step 2: Review the BGP configuration to verify the prefix filter is applied inbound to the BGP neighbor. To verify the BGP config and verify the prefix is applied, execute the command "show run | section router bgp".

router bgp 65000
  router-id 10.11.11.11
  address-family ipv4
    no neighbor 10.11.12.2 prefix-list out     
    neighbor 10.12.0.0 prefix-list LOCAL_SCOPE_BOUNDARY in

If the Arista router is not configured to reject inbound route advertisements belonging to the local AS, this is a finding.