Configuring Explicit Routing for MPLS

When you configure explicit routing rather than hop-by-hop routing for MPLS, the route the LSP takes is defined by the ingress node. The path consists of a series of hops defined by the ingress LSR. Each hop can be a traditional interface, an autonomous system, or an LSP.

MPLS explicit routing configuration tasks include the following sets of tasks:

• Defining Configured Explicit Paths
• Specifying Configured Explicit Paths on a Tunnel
• Configuring Dynamic Explicit Paths on a Tunnel

Defining Configured Explicit Paths

You can create explicit routing paths manually by configuring an explicit path with a name and a series of addresses (hops) from ingress to egress.

To manually configure explicit routing:

1. Define an explicit path and access Explicit Path Configuration mode.
   host1(config)#mpls explicit-path name xyz host1(config-expl-path)#
2. Do one of the following to configure the hops in the LSP:
   • Set the next hop (if need be) at a particular index in the explicit path.
     host1(config-expl-path)#index 5 next-address 172.18.100.5
   • Add the next hop (if need be) after a particular index in the explicit path.
     host1(config-expl-path)#append-after 5 next-address 192.168.47.22
3. Configure a next hop at the end of the MPLS explicit path.
   host1(config-expl-path)#next-address 10.10.9.2
4. Enable the explicit path.
   host1(config)#mpls explicit-path name xyz

   Note: To prevent a partially configured explicit path from being used, do not enable it until you have finished configuring or modifying the path.

5. (Optional) List the currently configured explicit path.
   host1(config-expl-path)#list 5

Specifying Configured Explicit Paths on a Tunnel

After you have defined a configured explicit path, you can configure the path on a tunnel.

To configure explicit routing on a tunnel:

1. Create an MPLS tunnel.
   host1(config)#interface tunnel mpls:1
2. Set the path option.
   host1(config-if)#tunnel mpls path-option 1 explicit name xyz

Configuring Dynamic Explicit Paths on a Tunnel

You can create explicit routing paths dynamically with a routing protocol. IS-IS and OSPF both currently support explicit routing.

To configure dynamic explicit routing:

1. Create an MPLS tunnel.
   host1(config)#interface tunnel mpls:bilbao5
2. Set the path option.
   host1(config-if)#tunnel mpls path-option 2 dynamic isis