VPN Terminology

VPNs include the following types of network devices (see Figure 1):

Provider edge (PE) routers—Routers in the provider’s network that connect to customer edge devices located at customer sites. PE routers support VPN and label functionality. (The label functionality can be provided either by the Resource Reservation Protocol [RSVP] or Label Distribution Protocol [LDP].) Within a single VPN, pairs of PE routers are connected through a tunnel, which can be either a Multiprotocol Label Switching (MPLS) label-switched path (LSP) or an LDP tunnel.
Provider (P) routers—Routers within the core of the provider’s network that are not connected to any routers at a customer site but are part of the tunnel between pairs of PE routers. P routers support MPLS LSP or LDP functionality, but do not need to support VPN functionality.
Customer edge (CE) devices—Routers or switches located at the customer site that connect to the provider’s network. CE devices are typically IP routers, but could also be an Asynchronous Transfer Mode (ATM), Frame Relay, or Ethernet switch.

VPN functionality is provided by the PE routers; the provider and CE routers have no special configuration requirements for VPNs.

Figure 1: Routers in a VPN

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