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
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:
- Define an explicit path and access Explicit Path Configuration
mode.host1(config)#mpls explicit-path name xyz host1(config-expl-path)#
- 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
- Set the next hop (if need be) at a particular index
in the explicit path.
- Configure a next hop at the end of the MPLS explicit
path.host1(config-expl-path)#next-address 10.10.9.2
- 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.
- (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:
- Create an MPLS tunnel.host1(config)#interface tunnel mpls:1
- 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:
- Create an MPLS tunnel.host1(config)#interface tunnel mpls:bilbao5
- Set the path option.host1(config-if)#tunnel mpls path-option 2 dynamic isis
| Note: If you configure the MPLS RSVP-TE tunnels to dynamically calculate the explicit path for the tunnels and if a router link-state advertisement (LSA) sends a metric of 65535 for one of the neighbors that is being considered while the Constrained Shortest Path First (CSPF) computation is performed, the metric that is sent in the router LSA is used in the CSPF calculation. Processing the router LSA by the CSPF algorithm ensures that the MPLS RSVP-TE tunnels are not retained in the down state and the tunnels come up properly. |
