V-254015

Discussion

Outbound route advertisements belonging to the core can result in traffic either looping or being black holed, or at a minimum, using a nonoptimized path.

Check Content

Review the BGP router configuration to verify that there is a filter defined to block route advertisements for prefixes that belong to the IP core. 

Verify an appropriate prefix-list containing the IP core prefixes is referenced in a policy-statement. For example:
[edit policy-options]
prefix-list ip-core-ipv4 {
    192.0.2.0/24;
}
prefix-list ip-core-ipv6 {
    2001:db8:2::/64;
}
policy-statement advertise-bgp-prefix {
    term exclude-ipv4-core {
        from {
            prefix-list ip-core-ipv4;
        }
        then reject;
    }
    term exclude-ipv6-core {
        from {
            prefix-list ip-core-ipv6;
        }
        then reject;
    }
    term default {
        then accept;
    }
}

The prefix filter must be referenced outbound on the appropriate BGP neighbor statements. For example:
[edit protocols]
bgp {
    group eBGP {
        type external;
        export advertise-bgp-prefix;
        neighbor 192.0.2.11 {
            export advertise-bgp-prefix;
        }
    }
    export advertise-bgp-prefix;
}

Note: Juniper routers support global, group, and neighbor export statements with the more specific definition taking precedence. Ensure more specific export policies (e.g., neighbor and group) do not reverse higher level export statements.

If the router is not configured to reject outbound route advertisements that belong to the IP core, this is a finding.