A site link bridge represents a set of site links which are capable of communicating with one another. Usually the site link bridge is a Router 
. A dedicated device or a multihomed computer configured for IP forwarding, which passes data packets from one network to another. or group of routers. Site link bridges maximize replication.
If your network is
fully routed, you do not need to create site link bridges because all site links for a specific protocol are bridged by default.