Supported Platforms
Disabling Constrained-Path LSP Computation
If the IGP is a link-state protocol (such as IS-IS or OSPF) and supports extensions that allow the current bandwidth reservation on each router’s link to be reported, constrained-path LSPs are computed by default.
The Junos implementations of IS-IS and OSPF include the extensions that support constrained-path LSP computation.
- IS-IS—These extensions are enabled by default. To disable this support, include the disable statement at the [edit protocols isis traffic-engineering] hierarchy level, as discussed in the Junos OS Routing Protocols Configuration Guide .
- OSPF—These extensions are disabled by default. To enable this support, include the traffic-engineering statement in the configurations of all routers running OSPF, as described in the Junos OS Routing Protocols Configuration Guide .
If IS-IS is enabled on a router or you enable OSPF traffic engineering extensions, MPLS performs the constrained-path LSP computation by default. For information about how constrained-path LSP computation works, see Constrained-Path LSP Computation.
Constrained-path LSPs have a greater chance of being established quickly and successfully for the following reasons:
- The LSP computation takes into account the current bandwidth reservation.
- Constrained-path LSPs reroute themselves away from node failures and congestion.
When constrained-path LSP computation is enabled, you can configure the LSP so that it is periodically reoptimized, as described in Optimizing Signaled LSPs.
When an LSP is being established or when an existing LSP fails, the constrained-path LSP computation is repeated periodically at the interval specified by the retry timer until the LSP is set up successfully. Once the LSP is set up, no recomputation is done. For more information about the retry timer, see Configuring the Connection Between Ingress and Egress Routers.
By default, constrained-path LSP computation is enabled. You might want to disable constrained-path LSP computation when all nodes do not support the necessary traffic engineering extensions. To disable constrained-path LSP computation, include the no-cspf statement:
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
If you disable constrained-path LSP computation on LSPs by configuring the no-cspf statement and then attempt to advertise other LSPs with lower metrics than the IGPs from this router in either IS-IS or OSPF, new LSPs cannot be established.
