Configuring SRLG group constraints

Shared Risk Loss Group (SRLG) is used to tag IP interfaces which share a specific fate with the same identifier. For example, an SRLG group identifier could represent all links which use separate fibers but are carried in the same fiber conduit. If the conduit is accidentally cut, all the fiber links are cut which means all IP interfaces using these fiber links fail. The user can enable the SRLG constraint to select a LFA next hop for a prefix which avoids all interfaces that share fate with the primary next.

The user first configures locally on each router the name and identifier of each SRLG group.

CLI syntax

config>router>if-attribute>srlg-group group-name value group-value

A maximum of 1024 SRLGs can be configured per system.

Next the user configures the admin group membership of the IP interfaces used in LFA. The user can apply SRLG groups to IES, VPRN, or network IP interface.

CLI syntax

config>router>if>if-attribute>srlg-group group-name [group-name...(up to 5 max)]
config>service>vprn>if>if-attribute>srlg-group groupname [group-name...(up to 5 max)]
config>service>ies>if>if-attribute>srlg-group groupname [group-name...(up to 5 max)]

The user can add a maximum of 64 SRLG groups to a specified IP interface. The same above command can be applied multiple times.

The no form of the srlg-group command under the interface deletes one or more of the SRLG memberships of the interface. It deletes all SRLG memberships if no group name is specified.

Finally, the user adds the SRLG constraint into the route next hop policy template.

CLI syntax

configure router route-next-hop-template template
 template-name
  srlg-enable

When this command is applied to a prefix, the LFA SPF selects a LFA next hop, among the computed ones, which uses an outgoing interface that does not participate in any of the SRLGs of the outgoing interface used by the primary next hop.