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MPLS and Traffic Engineering

Traffic engineering allows you to control the path that data packets follow, bypassing the standard routing model, which uses routing tables. Traffic engineering moves flows from congested links to alternate links that would not be selected by the automatically computed destination-based shortest path. With traffic engineering, you can:

Make more efficient use of expensive long-haul fibers.
Control how traffic is rerouted in the face of single or multiple failures.
Classify critical and regular traffic on a per-path basis.

The core of the traffic engineering design is based on building label-switched paths (LSPs) among routers. An LSP is connection-oriented, like a virtual circuit in Frame Relay or ATM. LSPs are not reliable: Packets entering an LSP do not have delivery guarantees, although preferential treatment is possible. LSPs also are similar to unidirectional tunnels in that packets entering a path are encapsulated in an envelope and switched across the entire path without being touched by intermediate nodes. LSPs provide fine-grained control over how packets are forwarded in a network. To provide reliability, an LSP can use a set of primary and secondary paths.

LSPs can be configured for Border Gateway Protocol (BGP) traffic only (traffic whose destination is outside of an autonomous system [AS]). In this case, traffic within the AS is not affected by the presence of LSPs. LSPs can also be configured for both BGP and interior gateway protocol (IGP) traffic; therefore, both intra-AS and inter-AS traffic is affected by the LSPs.

This section discusses the following topics:

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