A route distinguisher (RD) is a value that enables Multiprotocol Label Switching (MPLS)virtual private network (VPN) customers to use overlapping IP address ranges; MPLS VPNs are described in Request for Comments (RFC) 4364. An ingress label switch router (LSR) creates a globally unique VPN version 4 (VPNv4) address by adding the RD to the beginning of an IP address. The LSR then assigns a label to the VPNv4 address prefix and stores the inbound-to-outbound label mapping in the Label Forwarding Information Base (LFIB). Authentication to the MPLS VPN is provided based on logical port and RD information. To create an RD, you should issue the rd value command, where the valueparameter uses one of the following formats:
- AS:nn, where AS is a 16bit autonomous system number (ASN) and nn is a 32bit decimal number
- A.B.C.D:nn, where A.B.C.D is a 32bit IP address and nn is a 16bit decimal number

There are three types of RDs: Type 0, Type 1, and Type 2. The type of RD configuration you create depends on how you issue the value parameter of the rd command and whether you are configuring a multicast VPN environment. Type 0 and Type 1 RDs are used in unicast configurations. A Type 0 RD is configured by issuing the value parameter of the rd command with the 16bit ASN in front of the 32bit decimal number. A Type 1 RD is configured by issuing the value parameter of the rd command with the 32bit decimal number in front of the 16bit ASN. A Type 2 RD is configured similarly to a Type 1 RD but only applies to multicast VPN configurations.

A route target (RT) is a value that is appended to a VPNv4 Border Gateway Protocol (BGP)route to indicate membership in an RFC 4364 MPLS VPN. Export RTs associate each route with one or more VPNs, and import RTs are associated with each VPN routing and forwarding (VRF) table to determine the routes that should be imported into the VRF? a VRF is a routing table instance for a VPN. By configuring import and export RTs, you can configure which sites can reach each other.

For example, you can configure RTs so that CustomerA and CustomerB can communicate with ProviderZ, but CustomerA and CustomerB cannot communicate with one another. To configure RTs, you should issue the routetarget {import | export | both} value command, where the value parameter uses the same formats as the value parameter in the rd command.

A label switched path (LSP) is a path that labeled packets take through an MPLS network from one LSR to another. The 32bit MPLS label is used by LSRs to make forwarding decisions along the LSP. The MPLS label is placed between the Layer 2 header and the Layer 3 header.