V-283827

Discussion

Verifying the path a route has traversed will ensure the IP core is not used as a transit network for unauthorized or possibly 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 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.

Review the router bgp configuration to verify enforce-first-as is not configured, as shown in the example below: 

- configure router bgp group "eBGP"
- config>router>bgp>group# info
----------------------------------------------
                family ipv4
                peer-as 65540
                enforce-first-as
                neighbor 10.10.30.1
                exit
----------------------------------------------

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.