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MPLS Traffic Engineering and Signaling Protocols Overview

Traffic engineering facilitates efficient and reliable network operations while simultaneously optimizing network resources and traffic performance. Traffic engineering provides the ability to move traffic flow away from the shortest path selected by the interior gateway protocol (IGP) to a potentially less congested physical path across a network. To support traffic engineering, besides source routing, the network must do the following:

• Compute a path at the source by taking into account all the constraints, such as bandwidth and administrative requirements.
• Distribute the information about network topology and link attributes throughout the network once the path is computed.
• Reserve network resources and modify link attributes.

When transit traffic is routed through an IP network, MPLS is often used to engineer its passage. Although the exact path through the transit network is of little importance to either the sender or the receiver of the traffic, network administrators often want to route traffic more efficiently between certain source and destination address pairs. By adding a short label with specific routing instructions to each packet, MPLS switches packets from router to router through the network rather than forwarding packets based on next-hop lookups. The resulting routes are called label-switched paths (LSPs). LSPs control the passage of traffic through the network and speed traffic forwarding.

You can create LSPs manually, or through the use of signaling protocols. Signaling protocols are used within an MPLS environment to establish LSPs for traffic across a transit network. Junos OS supports two signaling protocols—LDP and the Resource Reservation Protocol (RSVP).

• MPLS LSPs for packet forwarding
• IGP extensions for distributing information about the network topology and link attributes
• Constrained Shortest Path First (CSPF) for path computation and path selection
• RSVP extensions to establish the forwarding state along the path and to reserve resources along the path

Junos OS also supports traffic engineering across different OSPF regions.