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# Traffic Engineering

Traffic engineering enables more effective use of network resources by providing for the setup of explicitly routed Multiprotocol Label Switching (MPLS) label-switched paths (LSPs) that satisfy resource and administrative constraints. You can use OSPF to exchange link resource and traffic-engineering administrative information between routers. OSPF uses this information to calculate paths in the network that satisfy the administrative constraints. MPLS can then set up LSPs along these paths. See JUNOSe BGP and MPLS Configuration Guide for a detailed discussion of MPLS.

## Configuring OSPF for Traffic Engineering

For OSPF to support traffic engineering, you must issue both of the following commands:

- mpls traffic-eng area—Enables the router to flood traffic engineering resource and administrative information in the specified area using type 10 opaque LSAs. These LSAs have an area-wide scope and therefore are flooded only within the indicated area.
- mpls traffic-eng router-id—Designates a router as traffic engineering capable and specifies the address of a stable router interface as the router ID of the node for traffic engineering purposes. The traffic engineering router ID serves as the tunnel endpoint for tunnels terminating at the node. Each node advertises its traffic engineering router ID in type 10 LSAs.

By default, OSPF always uses the MPLS tunnel to reach the MPLS endpoint. Best paths determined by SPF calculations are not considered. You can enable the consideration of best paths by issuing the mpls spf-use-any-best-path command. As a result, OSPF considers metrics for IGP paths and the tunnel metric, and might forward traffic along a best path, through the MPLS tunnel, or both.

You can use the show ip ospf database opaque-area command to display information about traffic engineering opaque LSAs.

For OSPF routes to use established MPLS tunnels as next hops—so that traffic can be mapped to use these tunnels—you must configure the tunnels with the tunnel mpls autoroute announce ospf command. See JUNOSe BGP and MPLS Configuration Guide, for information about configuring MPLS on a router.

mpls spf-use-any-best-path

- Use to enable SPF calculations to consider the IGP (OSPF) best paths as well as the MPLS tunnel for forwarding traffic to the MPLS endpoint.
- By default, the MPLS tunnel is always selected for traffic to the tunnel endpoint; IGP paths are not considered. For traffic beyond the endpoint, the tunnel is considered equally with any other path.
- Example
  `
  host1(config-router)#mpls spf-use-any-best-path
  `
- Use the no version to disable the use of IGP best paths.
- See mpls spf-use-any-best-path

mpls traffic-eng area

- Use to enable flooding of MPLS traffic engineering link information into the specified OSPF area. Flooding is disabled by default.
- Example
  `
  host1(config-router)#mpls traffic-eng area 0
  `
- Use the no version to disable flooding.
- See mpls traffic-eng area

mpls traffic-eng router-id

- Use to specify a stable interface to be used as a router ID for MPLS traffic engineering. Typically you specify a loopback interface to provide the greatest stability, because this is flooded to all nodes. The interface acts as the destination node for tunnels originating at other nodes.
- Example
  `
  host1(config-router)#mpls traffic-eng router-id loopback 0
  `
- Use the no version to remove the interface as a router ID.
- See mpls traffic-eng router-id

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