IS-IS Extensions to Support Traffic Engineering

To help provide traffic engineering and MPLS with information about network topology and loading, extensions have been added to the Junos implementation of IS-IS. Specifically, IS-IS supports new TLVs that specify link attributes. These TLVs are included in the IS-IS link-state PDUs. The link-attribute information is used to populate the traffic engineering database, which is used by the Constrained Shortest Path First (CSPF) algorithm to compute the paths that MPLS LSPs take. This path information is used by RSVP to set up LSPs and reserve bandwidth for them.

Note: Whenever possible, use IS-IS IGP shortcuts instead of traffic engineering shortcuts.

The traffic engineering extensions are defined in Internet draft draft-isis-traffic-traffic-02, IS-IS Extensions for Traffic Engineering.

IS-IS IGP Shortcuts

In IS-IS, you can configure shortcuts, which allow IS-IS to use an LSP as the next hop as if it were a subinterface from the ingress routing device to the egress routing device. The address specified on the to statement at the [edit protocols mpls label-switched-path lsp-path-name] hierarchy level must match the router ID of the egress routing device for the LSP to function as a direct link to the egress routing device and to be used as input to IS-IS SPF calculations. When used in this way, LSPs are no different than Asynchronous Transfer Mode (ATM) and Frame Relay virtual circuits (VCs), except that LSPs carry only IPv4 traffic.