How to Configure RSVP-Signaled LSPs on Junos Routers

By Walter J. Goralski, Cathy Gadecki, Michael Bushong

Imagine that you have a network where you’re carrying a lot of voice traffic. You want to make sure that voice traffic gets forwarded along a path that has enough bandwidth to support the load without congestion. And because voice packets can’t be received out of order, you want the entire voice flow to travel over the same path.

In this topology, you have a source of voice traffic (router 1) that is aggregating all your voice flows from various branch sites. You want to transport this data to headquarters, which requires sending the traffic through router 5 and off through the network and eventually to your headquarters.

You want to ensure that you have reserved bandwidth for all your flows, so you’re going to use RSVP as your LSP signaling protocol. To configure the LSP across your network, you must

  • Enable MPLS and RSVP on your router.

  • Enable RSVP and RSVP on your transit interfaces.

  • Configure your IGP to support traffic engineering.

  • Set up an LSP from the ingress to the egress router.

    An MPLS network using RSVP.

    An MPLS network using RSVP.

Enable MPLS and RSVP

Assuming that you’ve already set up your IGP and other routing protocols, the first thing you need to do to establish an RSVP LSP across your network is to enable both MPLS and RSVP on your routers.

You have to enable MPLS and RSVP across all the routers in your network, not just the ingress and egress routers. RSVP works by sending path messages and ensuring that all routers within an LSP can meet the bandwidth requirements for that particular path.

To enable these protocols:

[edit protocols]
rsvp {
   interface all;
}
mpls {
   interface all;
}

This configuration is pretty straightforward. By enabling the protocols on all interfaces, you avoid having to explicitly add each interface, which has the added benefit of making it easy to swap new interfaces in and out.

If you’re using management interfaces, you don’t want to run the signaling protocols across those LAN interfaces. You can prevent MPLS and RSVP from running on those interfaces by explicitly excluding them using the disable statement:

[edit protocols]
rsvp {
   interface all;
   interface fe-0/0/0.0 {
      disable;
   }
}
mpls {
   interface all;
   interface fe-0/0/0.0 {
      disable;
   }
}

Enable MPLS on your transit interfaces

After enabling MPLS and RSVP on your router, you must configure your transit interfaces.

You must enable MPLS on all the interfaces called out in the topology. To enable the protocols on a transit interface:

[edit interfaces]
fe-1/0/1 {
   unit 0 {
      family inet {
         address 10.0.24.1/24;
      }
      family mpls;
   }
}

Configure an LSP

After you have MPLS and RSVP turned on and ready to go, the only thing you need to do is to configure your LSP from router 1 to router 5. To configure an RSVP LSP, you must create an LSP on router 1 that points to router 5:

[edit protocols]
mpls {
   label-switched-path router1-to-router5 {
      to 10.0.0.5;
   }
}

Within the MPLS configuration, creating an LSP is as easy as naming it and identifying the remote loopback address of the router you want to use as your egress router for the LSP.

Creating an LSP that mirrors itself on the egress router is generally a good idea so that you can support bidirectional communication. In this case, you need to also configure on router 5:

[edit protocols]
mpls {
   label-switched-path router5-to-router1 {
      to 10.0.0.1;
   }
}

Verify the LSPs

After configuring something, you need to make sure that it works as expected. To verify the LSP configuration, use the show mpls lsp extensive command. If you issue the command from router 1, expect to see two separate LSPs, the one to router 5 and the one from router 5.