MPLS Route Distinguisher

When implementing MPLS VPNs, we use a Route Distinguisher or RD to allow PE routers to determine to which customer a particular prefix belongs.

RDs must be unique for different VRFs on the same PE, but for two corresponding VRFs on two different PEs, they may or may not be the same. In smaller deployments, you may find that administrators will configure them to be the same for simplicity, but in larger and more complex deployments, you'll find that they are different.

An RD should not be confused with a Route Target.

Links

https://networklessons.com/mpls/mpls-layer-3-vpn-explained#RD_Route_Distinguisher