MultiProtocol Label Switching (MPLS) is Originally developed by Cisco in the form of tag switching, MPLS was adopted as an Internet standard by the Internet Engineering Task Force (IETF). Service providers are the primary implementers of the technology. With MPLS networks, service providers can offer services similar to traditional WAN technologies at lower costs and provide additional IP-based services previously not available.

MPLS provides an encapsulation scheme that serves as an alternative to traditional routing. When a packet comes into the service provider edge, a router assigns a tag to the packet based on the destination IP network. The tag is a type of shorthand for a traditional IP-based route. After the tag is applied, the router forwards the packet into the MPLS core. The core routers read the label, apply the appropriate services, and forward the packet based on the label. As soon as the packet reaches the destination edge of the service provider network, the MPLS label is removed, and the IP packet is forwarded onto the IP network. One of the MPLS services that service providers offer is virtual private networks. Using MPLS labels, service providers can deliver IP-based services to many customers without the complexity of traditional Frame Relay or ATM circuit management. Customers can use private or public IP addressing without concern about overlapping other customer addressing. another opportunity of MPLS is because MPLS provides any-to-any connectivity. MPLS is divided into two layers or planes, each having a specific function in the network. The layers are the Control plane and the Data plane. The Data plane handles forwarding operations. The Control plane is responsible for the exchange of routing information (including labels) between adjacent devices.

Equipment and Stuff

Three primary equipment in MPLS are:

  1. CPE: This is equipment on the customer site. All traffic leaving the local site is routed through this point. This is often called customer equipment (CE).

  2. PE: Located at the ingress point of the SP network, this is the equipment that assigns (and removes) labels. The PE can either be routers or high-end switches. This is also referred to as the Edge Label Switch Router (ELSR).

  3. P: Located in the core of the SP network, provider (P) routers forward packets based on their labels. This is also called a Label Switch Router (LSR).

MPLS Labels

MPLS uses a label to decide where and how to send packets through the network. The label is applied at the ingress to the SP network and is removed at the network egress point. The only router responsible for adding the label is the network router that needs to process the entire packet header. The information contained in the header, along with the preconfigured instructions, is used to generate the label. Labels can be based on IP destinations (this is what traditional routing uses) and other parameters, such as IP sources, QoS, VPN membership, or specific routes for traffic engineering purposes. MPLS is also designed to support forwarding mechanisms from other protocols. Label information is distributed throughout the network using the Label Distribution Protocol (LDP). The

label assigned essentially keeps that packet separated from all other customers’ packets/cells. Because there is no place where one customer can view another customer’s packet/cells, there is no danger of having someone outside the SP network snoop for packets. Obviously this would not stop someone bent on illegally accessing a company’s information, but it does remove the possibility of someone claiming that he “accidentally” received the information.

MPLS router forward packets by using the label, but the router must know the relationship between a label and path through the network. This relationship is established and communicate throughout the network using Forwarding Equivalence Classes (FEC). A FEC is a specific path through the network of LSRs and is equal to the destination network, stored in an IP routing table. The LSRs simply look at the label and forward the packet based on the contents of the FEC. This is much simpler, faster, and more flexible than traditional IP routing.