If the Diameter request message is originated from a node (SRRP Active) that does not have direct connections to the agent or relevant Diameter servers, the request message must be sent to the inter peer which does have such connections. This is accomplished by designating the inter-peer as a default peer. A default peer is a peer used for all Diameter traffic that does not have an exact match for the destination-realm and application in the realm routing table. A default-peer is application (NASREQ/Gx/Gy) unaware. For routing loop avoidance information, see Diameter routing loop avoidance.
Because both redundant SR nodes have their default peers pointing to each other, a mechanism for routing loop prevention must be in place. This means that a Diameter message received from a peer, is never transmitted in the reverse direction back to this same peer (in other words, looped around).