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Example: Configuring MPLS LSP Link Protection

 
Figure 1: MPLS LSP Link Protection Topology Diagram
MPLS LSP Link Protection Topology
Diagram

In Figure 1, a primary MPLS LSP is established from Router 1 through Router 3 to destination Router 2. To implement link protection, include the link-protection statement on the primary LSP at the ingress point and on the appropriate downstream RSVP interfaces you wish to protect. In this case, the primary LSP named Protected_LSP on Router 1 requires link protection, as does the so-7/3/2 RSVP interface of Router 1 and the so-6/0/0 RSVP interface of Router 3. After link protection is enabled for the protected LSP, bypass LSPs are established automatically for the LSP-traversed interfaces of Routers 1 and 3.

On Router 1, configure an interior gateway protocol (IGP) routing protocol (in this case, IS-IS), RSVP, and MPLS on the so-0/0/0 and so-7/3/2 interfaces. Next, configure the primary LSP on Router 1 to point to the loopback address of Router 2. The primary LSP’s strict path must travel though Router 3.

Enable link protection on both the LSP itself and the outgoing RSVP interface traversed by the primary LSP (in this case, the so-7/3/2 RSVP interface of Router 1). After you enable link protection, the router notices that the primary LSP is protected and prepares a bypass LSP.

Configure a static route of 10.31.5.1 in the LSP on Router 1. You can use this route for testing purposes. Also, if you want to enable Packet Forwarding Engine local repair, establish a policy that requires all traffic to use per-packet load balancing. Once this policy is configured, export it to the neighboring routers with the export statement at the [edit routing-options forwarding-table] hierarchy level.

Router 1

On Router 2, no link protection configuration is needed. However, you should configure MPLS, RSVP, and IS-IS to communicate with the other routers.

Router 2

On Router 3, include IS-IS, RSVP, and MPLS on the so-1/0/0 and so-6/0/0 interfaces. Enable link protection on the remaining RSVP interface traversed by the primary LSP (in this case, the so-6/0/0 RSVP interface). After you enable link protection, the router notices the primary LSP is protected and prepares a bypass LSP.

To enable Packet Forwarding Engine local repair, establish a policy that requires traffic to use per-packet load balancing. Once this policy is configured, export it to the neighboring routers.

Router 3

Verifying Your Work

To verify proper operation of MPLS LSP link protection, use the following commands:

  • show mpls lsp

  • show route

  • show route forwarding-table

  • show rsvp interface detail

  • show rsvp neighbor detail

  • show rsvp session detail

The following sections show the output of these commands used with the configuration example:

Case 1: Normal Operation

Once link protection is enabled on the required RSVP interfaces and primary LSP, the bypass LSPs are prepared.

Router 1

user@Router1> show mpls lsp

This is the main LSP.

This is the bypass LSP from Router 3 to Router 2.

This is the main LSP. Notice that a backup LSP is not signaled when the main LSP is still up.

This is the bypass from Router 1 to Router 2. This also appears in the show mpls lsp command output above.

Link protection is enabled.

The number of backup routes equals 2 because the main LSP is already considered for protection.

This is the main LSP.

This is a backup route, though the backup LSP has not been signaled yet.

Packet Forwarding Engine local repair is enabled (otherwise, only one entry appears for Next-hop).

The Weight value for the backup starts at 20000 .

Router 3

user@Router3> show mpls lsp

The ingress bypass LSP to Router 2 does not appear here.

This is the ingress bypass session to Router 2 from Router 1.

This is the bypass from Router 1 to Router 3, arriving by way of Router 2.

This is the main LSP.

The number of backup routes is 1.

Link protection is enabled.

This is the main LSP.

This is the bypass LSP from Router 1 to Router 2.

Case 2: When the Link from Router 1 to Router 3 Is Disabled

The primary interface from Router 1 to Router 3 is disabled.

Router 1

user@Router1> show mpls lsp

The main LSP is up.

This is the bypass LSP from Router 3 to Router 2.

This is the newly signaled backup LSP, as indicated by the To/From field.

The original LSP is now down.

This is the bypass LSP from Router 1 to Router 2.

This is the bypass LSP from Router 3 to Router 2, which will fail in the next case.

The neighbor is down.

The route can be reached by way of the backup LSP.

Double-stacked labels appear on the backup LSP from Router 1 to Router 2 to Router 3.

Before proceeding to Case 3, reenable the so-7/3/2 interface on Router 1.

Case 3: When the Link from Router 3 to Router 2 Is Disabled

The primary interface from Router 3 to Router 2 is disabled.

Router 3

user@Router3> show rsvp session

The backup is signaled from Router 3 to Router 2.

The main LSP is down.

This is the backup LSP.

This shows label swapping for the main LSP traveling over the backup LSP through Router 2.

Router 1

user@Router1> show rsvp session detail

The main LSP is not affected.

The bypass LSP is listed, because Router 1 does not detect the backup from Router 3 to Router 2.

Labels are swapped on the bypass LSP.

There is only one entry here. The bypass to Router 3 is broken because the connection between Router 3 and Router 2 is disabled.

Only one entry is shown.