The Arista BGP router must be configured to reject route advertisements from BGP peers that do not list their autonomous system (AS) number as the first AS in the AS_PATH attribute.

Verifying the path a route has traversed will ensure the IP core is not used as a transit network for unauthorized or possibly even internet traffic. All autonomous system boundary routers (ASBRs) must ensure updates received from eBGP peers list their AS number as the first AS in the AS_PATH attribute.

The feature below is enabled by default.

Verify the BGP configuration to deny the updates received from eBGP peer that do not have the proper AS in the AS_PATH_attribute. To verify the BGP config and that the feature is applied, execute the command "show run all | in first".

router bgp 65001 bgp enforce-first-as

If the router is not configured for "enforce-first-as", this is a finding.

Configure all Arista ASBR routers to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute.

LEAF-1A(config)#router bgp 65001 LEAF-1A(config-router-bgp)#bgp enforce-first-as