Administrative groups (admin groups), also known as affinity, are used to tag IP interfaces which share a specific characteristic with the same identifier. For example, an admin group identifier could represent all links which connect to core routers, or all links which have bandwidth higher than 10G, or all links which are dedicated to a specific service.
The user first configures locally on each router the name and identifier of each admin group:
config>router>if-attribute>admin-group group-name value group-value
A maximum of 32 admin groups can be configured per system.
Next the user configures the admin group membership of the IP interfaces used in LFA. The user can apply admin groups to a network IP interface.
config>router> interface>if-attribute>admin-group group-name [group-name...(up to 5 max)]
The user can add as many admin groups as configured to a specific IP interface. The preceding command can be applied multiple times.
Note that the configured admin-group membership is applied in all levels/areas the interface is participating in. The same interface cannot have different memberships in different levels/areas.
The no form of the admin-group command under the interface deletes one or more of the admin-group memberships of the interface. It deletes all memberships if no group name is specified.
Finally, the user adds the admin group constraint into the route next-hop policy template:
configure router route-next-hop-template template template-name
include-group group-name [pref 1]
include-group group-name [pref 2]
exclude-group group-name
Each group is entered individually. The include-group statement instructs the LFA SPF selection algorithm to pick up a subset of LFA next-hops among the links which belong to one or more of the specified admin groups. A link which does not belong to at least one of the admin-groups is excluded. However, a link can still be selected if it belongs to one of the groups in a include-group statement but also belongs to other groups which are not part of any include-group statement in the route next-hop policy.
The pref option is used to provide a relative preference for the admin group to select. A lower preference value means that LFA SPF first attempts to select a LFA backup next-hop which is a member of the corresponding admin group. If none is found, then the admin group with the next higher preference value is evaluated. If no preference is configured for a specific admin group name, then it is supposed to be the least preferred, that is, numerically the highest preference value.
When evaluating multipleinclude-group statements within the same preference, any link which belongs to one or more of the included admin groups can be selected as an LFA next-hop. There is no relative preference based on how many of those included admin groups the link is a member of.
The exclude-group statement simply prunes all links belonging to the specified admin group before making the LFA backup next-hop selection for a prefix.
If the same group name is part of both include and exclude statements, the exclude statement wins. It other words, theexclude statement can be viewed as having an implicit preference value of 0.
Note the admin-group criterion is applied before running the LFA next-hop selection algorithm. The modified LFA next-hop selection algorithm is shown in Section 7.5.