Multiprotocol Label Switching (MPLS) is a mechanism in high-performance telecommunications networks that directs data from one network node to the next based on short path labels rather than long network addresses, avoiding complex lookups in a routing table. It is a mechanism used to transfer data across large data/voice/video networks.
Each packet entering an MPLS network is labeled with a locally significant MPLS label. As the packet passes through the MPLS network, label is replaced with another label or stripped off. The network distributes information so that each switch knows what it is supposed to do if it encounters a particular label by simply looking up the MPLS table. Thus, the router functionality is reduced to switch functionality, speeding up the data transfer significantly.
MPLS is a packet-forwarding technology which uses labels to make data forwarding decisions. The biggest advantage using MPLS is that the Layer 3 header analysis is done just once (when the packet enters the MPLS domain). Intermediate routers will not analyze the IP packet, thus saving valuable router resources, and greatly increasing the speed at which packets are forwarded. Label inspection drives subsequent packet forwarding. Further MPLS supports following applications:
Virtual Private Networking (VPN)
Traffic Engineering (TE)
Quality of Service (QoS)
Any Transport over MPLS (AToM)
Additionally, it decreases the forwarding overhead on the core routers. MPLS technologies are applicable to any network layer protocol
2.How MPLS works
Multi-Protocol Label Switching (MPLS) converts routed network to something closer to a switched network and offers information transfer speeds that are not available in a traditional IP-routed network. Instead of forwarding packets on a hop-by-hop basis, paths are established for particular source-destination pairs. The predetermined paths that make MPLS work are called label-switched paths (LSPs).
Routers in a LSP: Each router in LSP performs the following functions.
Ingress router-the router at the beginning of an LSP. This router encapsulates IP packets with an MPLS Layer 2 frame and forwards it to the next router in the path. Each LSP can have only one ingress router.
Egress router-The router at the end of an LSP. This router removes the MPLS encapsulation, thus transforming it from an MPLS packet to an IP packet, and forwards the packet to its final destination using information in the IP forwarding table. Each LSP can have only one egress router. The ingress and egress routers in an LSP cannot be the same router.
Transit router-any intermediate router in the LSP between the ingress and egress routers. Transit router forwards received MPLS packets to the next router in the MPLS path. An LSP can contain zero or more transit routers, up to a maximum of 253 transit routers in a single LSP.