Every advertised prefix contains an AS-Path attribute. However, in some cases this attribute can be empty.
For compatibility purposes, the IRP Bgpd has a few algorithms handling the AS-Path attribute:
- The advertised prefix will be marked with a recovered AS-Path attribute.
Recovered AS-Path is composed of consecutive AS-Numbers that are collected during exploring process. Please note that recovered AS-Path may differ from the actual BGP Path. - The advertised prefix will be marked with the AS-Path from the aggregate received via BGP.
- If the advertised prefix, for whatever reason, has an empty AS-Path, it can be announced or ignored, depending on the Bgpd configuration.
For a detailed description refer to bgpd.as_path.
In case certain routes should be preferred over decisions made by IRP, use one of the following ways:
– Routers may be configured to have more preferable localpref / weight values for such routes so the best path algorithm always selects these routes instead of the routes injected by the Bgpd daemon.
– Routes may be filtered or have lower localpref / weight set up, using incoming route-map applied to BGP session with IRP.
– Networks that must be completely ignored by IRP can be specified in global.ignored.asn, global.ignorednets parameters or marked with a BGP Community listed in global.ignored_communities, so no probing / improving / announcing will be made by IRP.
If split announcements are enabled in IRP (refer bgpd.updates.split) the routes announced by IRP will be more specific.