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backup-selection (Protocols IS-IS)

 

Syntax

Hierarchy Level

Release Information

Statement introduced in Junos OS Release 14.1.

Description

Define backup selection policies, per prefix per primary next-hop interface, to enforce loop-free alternate (LFA) selection based on admin-group, srlg, bandwidth, protection-type, node, node-tag, and metric attributes of the backup path.

The remaining statements are explained separately. See CLI Explorer.

Options

destination prefixDefine the backup selection policy for a particular destination prefix or for all the prefixes. The prefix is the destination prefix name and prefix length. You can specify 0/0 for the IPv4 least-specific prefix or 0::0/0 for the IPv6 least-specific prefix.
interfaceDefine the backup selection policy for a specific primary next hop.
interface-name Name of the primary next-hop interface.
all All the interfaces.
bandwidth-greater-equal-primary Allow the selection of the backup next hop only if the bandwidth is greater than or equal to the bandwidth of the primary next hop.
dest-metric (highest | lowest)Specifiy the metric from the one-hop neighbor or from the remote router such as an RSVP backup label-switched-path (LSP) tail-end router to the final destination.
highest Select the backup path that has the highest destination metric.
lowest Select the backup path that has the lowest destination metric.
downstream-paths-only Select the backup path that is a downstream path to the destination.
evaluation-order [ admin-group srlg bandwidth protection-type neighbor neighbor-tag metric ]Control the order and the criteria of evaluating the backup path. The default order of evaluation is admin-group, srlg, bandwidth, protection-type, neighbor, neighbor-tag, and metric.
Note

For the explicitly configured evaluation order, only the listed attributes influence the selection of the backup path.

metric-order [ root dest ] Specify the order of preference of the root and the destination metric during the backup path selection. The preference order can be:
  • [root dest] — Backup path selection or preference is first based on the root-metric criteria. If the criteria of all the root-metric is the same, then the selection or preference is based on the dest-metric.

  • [dest root] — Backup path selection or preference is first based on the dest-metric criteria. If the criteria of all the dest-metric is the same, then the selection is based on the root-metric.

Note

By default, backup paths with lower destination metric criteria are selected or preferred. If the criteria is the same, then the lowest root metric criteria is preferred or selected.

root The metric to a one-hop neighbor or a remote router.
dest The metric from a one-hop neighbor or remote router to the final destination.
protection-type (link | node | node-link)Specify the required protection type of the backup path.
Note

If no protection-type is configured, then by default the first best path that matches all the other criteria is executed.

link Select the backup path that provides link protection.
node Select the backup path that provides node protection.
node-link Allow either node or link protection LFA where node-protection LFA is preferred over link-protection LFA.
root-metric (highest | lowest)Specify the metric to the one-hop neighbor or to the remote router such as an RSVP backup label-switched-path (LSP) tail-end router.
highest Select the highest root metric.
lowest Select the lowest root metric.
srlg (loose | strict)Define the backup selection to either allow or reject the common shared risk link groups (SRLGs) between the primary link and any link in the backup path.
loose Allow the backup path that has common srlgs between the primary link and any link in the backup path. A backup path with a fewer number of srlg collisions is preferred.
strict Reject the backup path that has common srlgs between the primary link and each link in the backup path.
nodeDefine a list of loop-back IP addresses of the adjacent nodes to either prefer or exclude in the backup path selection. The node can be a local (adjacent router) node, remote node, or any other router in the backup path.
Note

The nodes are identified through the TE-router-ID TLV advertised by a node in the LSP.

exclude [ node-address ] Specify the list of nodes to be excluded. The backup path that has a router from the list is not selected as the loop-free alternative or backup next hop.
node-address Name of one or more nodes to be excluded during backup path selection.
preference [ node-address ] Define an ordered set of nodes to be preferred. The backup path having the leftmost node is selected.
node-address Name of one or more nodes to be preferred in the backup path selection.
node-tagDefine per-neighbor policy to either prefer or exclude a backup path.
Note

This statement identifies a group of nodes in the network based on criteria such as the same neighbor tag values for all PE nodes. This is implemented using IS-IS admin-tags.

exclude [ node-address ] Specify the list of nodes to be excluded. The backup path that has a router from the list is not selected as the loop-free alternative or backup next hop.
node-address Name of one or more nodes to be excluded during backup path selection.
preference [ node-address ] Define an ordered set of nodes to be preferred. The backup path having the leftmost node is selected.
node-address Name of one or more nodes to be preferred in the backup path selection.

The remaining statements are explained separately. See CLI Explorer.

Required Privilege Level

routing—To view this statement in the configuration.

routing-control—To add this statement to the configuration.