V-253978

Discussion

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.

Check Content

Review the BGP router configuration to verify the router is configured to deny updates received from eBGP peers that do not list their AS number as the first AS in the AS_PATH attribute.

Verify the configuration of "enforce-first-as" at either the BGP global or group level.
[edit protocols bgp]
group eBGP {
    enforce-first-as;
    neighbor <address>;
}
enforce-first-as;

If the router is not configured to reject updates from peers that do not list their AS number as the first AS in the AS_PATH attribute, this is a finding.