V-217054

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

Verify a prefix list has been configured containing prefixes belonging to the local autonomous system as shown in the example below.

policy-options {
    …
    …
    …
    prefix-list OUR_PREFIXES {
        x.x.x.x/16;
    }

Verify that a policy has been configured to reject the local prefixes.

policy-options {
    …
    …
    …
    policy-statement FILTER_ROUTES {
        term REJECT_BOGONS {
            from {
                prefix-list BOGON_PREFIXES;
            }
            then reject;
        }
        term REJECT_OUR_PREFIXES {
            from {
                prefix-list OUR_PREFIXES;
            }
            then reject;
        }
        term ACCEPT_OTHER {
            then accept;
        }
    }
}

Verify that the configured policy to filter local prefixes has been applied to external BGP peers as shown in the example below.

protocols {
    bgp {
        group GROUP_AS4 {
            type external;
            import FILTER_ROUTES;
            peer-as 4;
            neighbor x.x.x.x;
        }
    }

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