MPLS and IP

MPLS cannot be compared to IP as a separate entity because it works in conjunction with IP and IP's IGP routing protocols. MPLS LSPs provide dynamic, transparent virtual networks with support for traffic engineering, the ability to transport Layer-3 (IP) VPNs with overlapping address spaces, and support for Layer-2 pseudowires using Pseudowire Emulation Edge-to-Edge (PWE3) that are capable of transporting a variety of transport payloads (IPv4, IPv6, ATM, Frame Relay, etc). MPLS-capable devices are referred to as LSRs. LSR devices provide traffic engineering functions can be defined using explicit hop-by-hop configuration,dynamically routed by the Constrained Shortest Path First (CSPF) algorithm, or configured as a loose route that avoids a particular IP or that is partly explicit and partly dynamic.

In a pure IP network, the shortest path to a destination is chosen even when it becomes more congested. Meanwhile, in an IP network with MPLS Traffic Engineering CSPF routing, constraints such as the RSVP bandwidth of the traversed links can also be considered, such that the shortest path with available bandwidth will be chosen. MPLS Traffic Engineering relies upon the use of TE extensions to OSPF or IS-IS and RSVP. Besides the constraint of RSVP bandwidth, users can also define their own constraints by specifying link attributes and special requirements for tunnels to route (or not to route) over links with certain attributes.

August 9, 2011

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