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Beginner

Why does ISIS need to be enabled on an interface?

I am currently doing a lab with ISIS, EIGRP and OSPF all included in the same topology.  One of the problems mentions that ISIS has to be enabled on an interface to work properly.  As far as I know, no other routing protocol needs to be enabled on an interface to propagate.  Why is this?  Thanks for answering!

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Cisco Employee

Re: Why does ISIS need to be enabled on an interface?

Hi,

 

it is probably an implementation decision. I am not aware of any technical limitation that needs ISIS to be enabled on a per interface basis. The procedure of enabling ISIS on a per interface basis is for IOS and OSPFv3 introduces similar configuration approach in IOS.

 

IOS-XR configuration is different and any IGP protocol follows the below:

 

router <igp-type> <instance>

interface <interface-num>

address-family <>

...

NXOS follows the IOS format. So I think it is just implementation matter.

 

HTH,

Nagendra

VIP Mentor

Re: Why does ISIS need to be enabled on an interface?

Hello,

 

in addition to Nagendra's post, if you are referring to the below:

 

Interface Serial0
ip address 192.168.1.1 255.255.255.0
ip router isis

!
router isis
net 47.0002.1910.2800.1001.00

 

and 

 

Interface Serial0
ip address 192.168.1.1 255.255.255.0

!
router ospf 1
network 192,168.1.0 0.0.0.255 area 0

 

The difference is that in IS-IS, there is no relation between the net number and the IP address, whereas in OSFP/EIGRP/RIP, you are basically enabling the routing process for the IP addresses specified with the 'network' command.

 

Does that make sense ?

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