Supported Platforms
Configuring Fast Reroute
Fast reroute provides a mechanism for automatically rerouting traffic on an LSP if a node or link in an LSP fails, thus reducing the loss of packets traveling over the LSP.
To configure fast reroute on an LSP, include the fast-reroute statement on the ingress router:
You can include this statement at the following hierarchy levels:
- [edit protocols mpls label-switched-path lsp-name]
- [edit logical-systems logical-system-name protocols mpls label-switched-path lsp-name]
You do not need to configure fast reroute on the LSP’s transit and egress routers. Once fast reroute is enabled, the ingress router signals all the downstream routers that fast reroute is enabled on the LSP, and each downstream router does its best to set up detours for the LSP. If a downstream router does not support fast reroute, it ignores the request to set up detours and continues to support the LSP. A router that does not support fast reroute will cause some of the detours to fail, but otherwise has no impact on the LSP.
 | Note: To enable PFE fast reroute, configure a routing policy statement with the load-balance per-packet statement at the [edit policy-options policy-statement policy-name then] hierarchy level on each of the routers where traffic might be rerouted. See also Configuring Load Balancing Across RSVP LSPs. |
By default, no bandwidth is reserved for the rerouted path. To allocate bandwidth for the rerouted path, include either the bandwidth statement or the bandwidth-percent statement. You can only include one of these statements at a time. If you do not include either the bandwidth statement or the bandwidth-percent statement, the default setting is to not reserve bandwidth for the detour path.
When you include the bandwidth statement, you can specify the specific amount of bandwidth (in bits per second [bps]) you want to reserve for the detour path. The bandwidth does not need to be identical to that allocated for the LSP.
When you specify a bandwidth percent using the bandwidth-percent statement, the detour path bandwidth is computed by multiplying the bandwidth percentage by the bandwidth configured for the main traffic-engineered LSP. For information about how to configure the bandwidth for a traffic-engineered LSP, see Configuring LSPs for DiffServ-Aware Traffic Engineering.
Hop-limit constraints define how many more routers a detour is allowed to traverse compared with the LSP itself. By default, the hop limit is set to 6. For example, if an LSP traverses 4 routers, any detour for the LSP can be up to 10 (that is, 4 + 6) router hops, including the ingress and egress routers.
By default, a detour inherits the same administrative (coloring) group constraints as its parent LSP when CSPF is determining the alternate path. Administrative groups, also known as link coloring or resource class, are manually assigned attributes that describe the “color” of links, such that links with the same color conceptually belong to the same class. If you specify the include-any statement when configuring the parent LSP, all links traversed by the alternate session must have at least one color found in the list of groups. If you specify the include-all statement when configuring the parent LSP, all links traversed by the alternate session must have all of the colors found in the list of groups. If you specify the exclude statement when configuring the parent LSP, none of the links must have a color found in the list of groups. For more information about administrative group constraints, see Configuring Administrative Groups.
