BGP RR Loop Prevention

Hello Hobbit,

The cluster ID is used to prevent loops between RRs.

Similar to an AS_Path, a Cluster_List is composed of a series of Cluster_IDs and is generated by an RR. The Cluster_List records all the RRs through which a route passes.

• Before an RR reflects a route between its clients or between its clients and non-clients, the RR adds the local Cluster_ID to the head of the Cluster_List. If a route does not carry any Cluster_List, the RR creates one for the route.

• After the RR receives an updated route, it checks the Cluster_List of the route. If the RR finds that its cluster ID is included in the Cluster_List, the RR discards the route. If its cluster ID is not included in the Cluster_List, the RR adds its cluster ID to the Cluster_List and then reflects the route.

The Originator_ID is used to prevent loops between clients.

The Originator_ID attribute is four bytes long and is generated by an RR. It carries the router ID of the route originator in the local AS.

• When a route is reflected by an RR for the first time, the RR adds the Originator_ID to this route. If a route already carries the Originator_ID attribute, the RR does not create a new one.

• After receiving the route, a BGP speaker checks whether the Originator_ID is the same as its router ID. If Originator_ID is the same as its router ID, the BGP speaker discards this route.