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Configuring MPLS over GRE Tunnels

MPLS LSPs can use generic routing encapsulation (GRE) tunnels to cross routing areas, autonomous systems, and ISPs. Bridging MPLS LSPs over an intervening IP domain is possible without disrupting the outlying MPLS domain.

LSPs can reach any destination that the GRE tunnels can reach. MPLS applications can be deployed without requiring all transit nodes to support MPLS, or requiring all transit nodes to support the same label distribution protocols (LDP or RSVP). If you use CSPF, you must configure OSPF or IS-IS through the GRE tunnel. Traffic engineering is not supported over GRE tunnels; for example, you cannot reserve bandwidth or set priority or preemption.

Note: Use the no-control word statement to disable the control word when the topology uses generic routing encapsulation (GRE) as the connection mechanism between PEs, and one of the PEs is an M-series router.

For more information about GRE tunnels, see the JUNOS Services Interfaces Configuration Guide.

Example: Configuring MPLS over GRE Tunnels

To configure MPLS over GRE tunnels:

  1. Enable family mpls under the GRE interface configuration:
    [edit interfaces]
    interface gr-1/2/0 {
    unit 0 {
    tunnel {
    source 192.168.1.1;
    destination 192.168.1.2;
    }
    family inet {
    address 5.1.1.1/30;
    }
    family iso;
    family mpls;
    }
    }
  2. Enable RSVP and MPLS over the GRE tunnel:
    [edit protocols]
    rsvp {
    interface gr-1/2/0.0;
    }
    mpls {
    ...
    interface gr-1/2/0.0;
    }
  3. Configure LSPs to travel through the GRE tunnel endpoint address:
    [edit protocols]
    mpls {
    label-switched-path gre-tunnel {
    to 5.1.1.2;
    ...
    }
    }

Standard LSP configuration options apply. If the routing table specifies that a particular route will traverse a GRE tunnel, the RSVP packets will traverse the tunnel as well.

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