What Is an MPLS VPN?
MPLS VPN is a technology that uses MPLS to construct VPNs on an IP backbone network. The essence of VPN is to transmit service data across a public network as if it was on a private network. This requires a tunnel to be set up on the public network so that data packets can be transmitted directly to the destination through the tunnel. Generally, MPLS VPN uses LSPs established using MPLS as public network tunnels to transmit private network service data.
VPN technology has been around longer than MPLS. ATM or Frame Relay technologies providing VPN facilities at Layer 2 were very popular. In such a network, the service provider runs ATM or Frame Relay to provide connectivity, which typically forms the backbone network. In case of MPLS VPN, MPLS forms the backbone network over which VPN services are provided. A virtual network built on top of existing network infrastructure(Underlay) is called an Overlay. This technique of overlaying a virtual network on an underlay increases the scalability of the network and supports multi-tenancy, modularity and virtualization.
The basic MPLS VPN model consists of the following roles:
Customer edge (CE): an edge device on a user network. A CE is directly connected to a service provider (SP) network through interfaces. The VPN sites of users are connected to the SP network through the CE. A CE can be a network device or a host. Generally, CEs are unaware of VPNs and do not need to support MPLS.
Provider edge (PE): an edge device on an SP network. A PE is directly connected to a CE. On an MPLS network, PEs function as LSRs and process all MPLS and VPN services. This places high requirements on the performance of PEs.
Provider (P): a backbone device on an SP network. A P is not directly connected to a CE. On an MPLS network, a P functions as an LSR and only needs to process MPLS services. It does not need to maintain VPN information.
Basic MPLS VPN model
MPLS VPN fully leverages the technical advantages of MPLS and is the most widely used VPN technology. MPLS VPN offers the following benefits to users:
An MPLS label corresponds to the data flow of a specified service (specific FEC), which helps to isolate services of different users.
MPLS provides TE and QoS capabilities. Users can use MPLS to fully optimize VPN resource configuration.
In addition, MPLS VPN provides flexible policy control to meet the special requirements of different users and implement value-added services quickly.
