In a Diameter multi-chassis configuration, the SR node with SRRP in an Active state (where the subscriber is active) and the SR node with open relevant Diameter peering connections may not be co-located. As a result, it is possible that the RAR message is received on the SR node where the Diameter application (for example, Gx) is not active. In this case, the RAR message is re-routed from the default peer to the peering SR node where the SRRP is in the Active state, and the Diameter application is active.
If the default peer is not available, the RAR message is dropped and a DIAMETER_UNABLE_TO_DELIVER error message is sent back to the peer from which the RAR message was received.