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Configuring Multiclass LSPs


A multiclass LSP is an LSP configured to reserve bandwidth for multiple class types and also carries the traffic for these class types. The differentiated service behavior is determined by the EXP bits.

You must configure the Differentiated Services domain (see Configuring Routers for DiffServ-Aware Traffic Engineering) before you can enable a multiclass LSP. The Differentiated Services domain provides the underlying class types and corresponding traffic engineering classes that you reference in a multiclass LSP configuration. The traffic engineering classes must be configured consistently on each router participating in the Differentiated Services domain for the multiclass LSP to function properly.


You must configure extended MAM as the bandwidth model when you configure multiclass LSPs. See Configuring the Bandwidth Model.

All the routers participating in a multiclass LSP must be Juniper Networks routers running Junos OS Release 6.2 or later. The network can include routers from other vendors and Juniper Networks routers running earlier versions of the Junos OS. However, the multiclass LSP cannot traverse these routers.

To enable multiclass LSPs, you need to configure the following:

Configuring Class of Service for the Interfaces

The existing class-of-service infrastructure ensures that traffic that is consistently marked receives the scheduling guarantees for its class. The classification, marking, and scheduling necessary to consistently mark traffic are configured with the existing Junos OS CoS features.


The Junos OS does not support ATM interfaces.

For information about how to configure CoS, see the Class of Service User Guide (Routers and EX9200 Switches).

Configuring the IGP

You can configure either IS-IS or OSPF. The IS-IS and OSPF configurations for routers supporting multiclass LSPs are standard. For information about how to configure these protocols, see the Junos OS Routing Protocols Library.

Configuring Class-Type Bandwidth Constraints for Multiclass LSPs

You configure a multiclass LSP by using the standard LSP configuration statements and procedures. To configure an LSP as a multiclass LSP, specify the class type bandwidth constraints by including the bandwidth statement:

For a list of hierarchy levels at which you can include the bandwidth statement, see the statement summary sections for these statements.

The class type statements specify bandwidth (in bits per second) for the following classes:

  • ct0—Bandwidth reserved for class 0

  • ct1—Bandwidth reserved for class 1

  • ct2—Bandwidth reserved for class 2

  • ct3—Bandwidth reserved for class 3

For example, to configure 50 megabytes of bandwidth for class type 1 and 30 megabytes of bandwidth for class type 2, include the bandwidth statement as follows:

You cannot configure a bandwidth for a class type and also configure a bandwidth at the [edit protocols mpls label-switched-path lsp-name bandwidth] hierarchy level. For example, the following configuration cannot be committed:

You can configure setup and holding priorities for a multiclass LSP, but the following restrictions apply:

  • The setup and holding priorities apply to all classes for which bandwidth is requested.

  • The combination of class and priority must be one of the configured traffic engineering classes. The default traffic engineering class configuration results in multiclass LSPs that cannot preempt and cannot be preempted. The default setup priority is 7 and the default holding priority is 0.

  • Configuring an invalid combination of class type and priority causes the commit operation to fail.

  • Automatic bandwidth allocation is not supported for multiclass LSPs. If you configure automatic bandwidth allocation, the commit operation fails.

  • LSPs configured with the bandwidth statement but without specifying a class type use the default class type ct0.

Configuring Policing for Multiclass LSPs

Policing allows you to control the amount of traffic forwarded through a particular multiclass LSP. Policing helps to ensure that the amount of traffic forwarded through an LSP never exceeds the requested bandwidth allocation. You can configure multiple policers for each multiclass LSP. You can also enable automatic policing for multiclass LSPs.

For information about how to configure a policer for a multiclass LSP, see Configuring Policers for LSPs and Configuring Automatic Policers.

Configuring Fast Reroute for Multiclass LSPs

You can enable fast reroute for multiclass LSPs. The bandwidth guarantees for the class types can be carried over to the detour path in case the primary path of the multiclass LSP fails. The same traffic class types configured for the primary multiclass LSP are also signaled for the detour LSP.

The bandwidth guarantee for the detour path is a percentage of the bandwidth configured for the class types of the primary path. For example, you configure a value of 50 percent for the detour path and the protected LSP carries traffic for class types CT0 through CT3. The detour path is signaled with the same class types (CT0 through CT3) but with 50 percent of the bandwidth configured for the protected LSP.

If you configure the router to reserve bandwidth for the detour path, a check is made to ensure that the link is capable of handling DiffServ-aware traffic engineering, that all of the traffic class types needed are available, and for CoS capability before accepting it as a potential detour path. Unsupported links are not used.

The bandwidth percentage for fast reroute is signaled from the ingress router to the egress router. All of the intermediate devices must complete their own CSPF computations and signaling.

When you configure the bandwidth-percent statement, the detour path bandwidth is computed by multiplying by the bandwidth configured for the primary multiclass LSP. For information about how to configure the bandwidth for the multiclass LSP, see Configuring Traffic-Engineered LSPs.

To configure the percentage of bandwidth used by the detour path based on the bandwidth of the protected path, include the bandwidth-percent statement:

You can include this statement at the following hierarchy levels: