Advertise an interface in ISIS without ip router isis

Posted on April 4, 2010

When configuring ISIS on an interface (a loopback for example) you something find the constraint “Advertise the Loopback0 in ISIS, do not use ip router isis and the prefixes should appear as internal ISIS routes”.

Lets take in another way, ever wondered why ip router isis disappears when you type passive-interface ?

SPRack1R1(config-if)#do sh run int lo0
Building configuration...

Current configuration : 85 bytes
!
interface Loopback0
 ip address 24.1.1.1 255.255.255.255
 no clns route-cache
end

SPRack1R1(config-if)#int lo0
SPRack1R1(config-if)#ip router isis
SPRack1R1(config-if)#do sh run int lo0
Building configuration...

Current configuration : 81 bytes
!
interface Loopback0
 ip address 24.1.1.1 255.255.255.255
 ip router isis
end

SPRack1R1(config-if)#router isis
SPRack1R1(config-router)#passive lo0
SPRack1R1(config-router)#do sh run int lo0
Building configuration...

Current configuration : 64 bytes
!
interface Loopback0
 ip address 24.1.1.1 255.255.255.255
end

SPRack1R1(config-router)#

Strange Uh ? But actually it does the job, you don’t need to put ip router isis as the passive interface implies it’s in the domain !

SPRack1R4(config-router)#do sh ip route | i 24.1.1.1
i L2    24.1.1.1/32 [115/10] via 24.1.14.1, Serial0/0/0.14

Great stuff no ?


No Replies to "Advertise an interface in ISIS without ip router isis"


    Got something to say?

    Some html is OK