The Arista BGP router must be configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer.

The effects of prefix de-aggregation can degrade router performance due to the size of routing tables and also result in black-holing legitimate traffic. Initiated by an attacker or a misconfigured router, prefix de-aggregation occurs when the announcement of a large prefix is fragmented into a collection of smaller prefix announcements.

This requirement is not applicable for the DODIN backbone.

Review the Arista router configuration to verify there is a filter to reject inbound route advertisements that are greater than /24 or the least significant prefixes issued to the customer, whichever is larger.

Step 1: To verify there is a filter to reject inbound route advertisements that are greater than /24 or the least significant prefixes issued to the customer, whichever is larger, execute the command "sh ip prefix-list".

ip prefix-list ADVERTISE_ROUTES deny 0.0.0.0/0 ge 25 ip prefix-list ADVERTISE_ROUTES permit 0.0.0.0/0 le 32

Step 2: Verify the prefix-list is applied in BGP process. Execute the command "sh run section router bgp".

router bgp 65000 neighbor 10.1.12.2 prefix-list ADVERTISE_ROUTES in

If the Arista router is not configured to limit the prefix size on any inbound route advertisement to /24 or the least significant prefixes issued to the customer, this is a finding.

This requirement is not applicable for the DODIN backbone.

Ensure all eBGP Arista routers are configured to limit the prefix size on any route advertisement to /24 or the least significant prefixes issued to the customer.

Step 1: Configure the prefix-list.

ip prefix-list ADVERTISE_ROUTES deny 0.0.0.0/0 ge 25 ip prefix-list ADVERTISE_ROUTES permit 0.0.0.0/0 le 32

Step 2: Apply the prefix-list in the BGP process inbound.

LEAF-1A(config)#router bgp 65000 LEAF-1A(config)# neighbor 10.1.12.2 prefix-list ADVERTISE_ROUTES in