Packet Forwarding with Multiprotocol Label Switching

Label Switching (MPLS) is an emerging technology that aims to address many of the existing issues associated with packet forwarding in today's Internetworking environment. It provides a method of forwarding packets at a high rate of speed by combining the speed and performance of Layer 2 with the scalability and IP intelligence of Layer 3. In a traditional IP (Internet Protocol) routing network, a router analyzes the destination IP address contained in the packet header. The router independently determines the next hop for the packet using the destination IP address and the interior gateway protocol. This process is repeated at each hop to deliver the packet to its final destination. In contrast, in the MPLS forwarding paradigm routers on the edge of the network (label edge routers) attach labels to packets based on the forwarding Equivalence class (FEC). Packets are then forwarded through the MPLS domain, based on their associated FECs , through swapping the labels by routers in the core of the network called label switch routers. The act of simply swapping the label instead of referencing the IP header of the packet in the routing table at each hop provides a more efficient manner of forwarding packets, which in turn allows the opportunity for traffic to be forwarded at tremendous speeds and to have granular control over the path taken by a packet. This paper deals with the process of MPLS forwarding mechanism, implementation of MPLS datapath , and test results showing the performance comparison of MPLS and IP routing. The discussion will focus primarily on MPLS IP packet networks — by far the most common application of MPLS today. I. TRADITIONAL IP ROUTING N traditional routing environments, a packet is forwarded through a network on a hop-by-hop basis using interior gateway protocols (IGPs) such as routing information protocol (RIP) and open shortest path first (OSPF), or exterior gateway protocol (EGPs) such as border gateway protocol (BGP). IP packets contain a header with sufficient information that enables them to be forwarded through a network. Traditionally packet forwarding has been based upon datagram routing. The routing technique used in IP networks is a destination-based routing paradigm. This means that an IP packet is routed through the network based upon the destination address contained within the packet header [5]. The forwarding mechanism utilized by IP networks is "hop-by-hop" routing, which means that every packet entering a router is examined and …