The user can instruct IGP to not include all interfaces participating in a specific IS-IS level or OSPF area in the SPF LFA computation. This provides a way of reducing the LFA SPF calculation where it is not needed.
config>router>isis>level>loopfree-alternate-exclude config>router>ospf>area>loopfree-alternate-exclude
If IGP shortcut are also enabled in LFA SPF, the LSPs with destination address in that IS-IS level or OSPF area are also not included in the LFA SPF calculation.
The user can also exclude a specific IP interface from being included in the LFA SPF computation by IS-IS or OSPF:
config>router>isis>interface>loopfree-alternate-exclude config>router>ospf>area>interface> loopfree-alternate-exclude
When an interface is excluded from the LFA SPF in IS-IS, it is excluded in both level 1 and level 2. When the user excludes an interface from the LFA SPF in OSPF, it is excluded in all areas. However, the above OSPF command can only be executed under the area in which the specified interface is primary and when enabled, the interface is excluded in that area and in all other areas where the interface is secondary. If the user attempts to apply it to an area where the interface is secondary, the command fails.
Finally, the user can apply the same above commands for an OSPF instance within a VPRN service:
config>service>vprn>ospf>area>loopfree-alternate-exclude config>service>vprn>ospf>area>interface>loopfree-alternate-exclude