urgent help MPLS needed

Unanswered Question
Nov 10th, 2008
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guys we have 4 sites A,B,C,D all are connected via dark fiber (ethernet).

connection is

A --->C

C---> D



now A is also connected with ---D


ISIS is the routing protocol

all routers have loopbacks as well

now all physical interfaces should be in area 43.0010 and shd run level 1

now site BC loopback interfaces should be in same area as above and should run level 1 as well.

site A and D loopback should be in different area 47.2010 and should run level 2

the problem is its poretty straight forward but i am nnot allowed to use seperate instance of ISIS i m going nuts is it possible if yes how....thanks for your help guys.....

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Mohamed Sobair Mon, 11/10/2008 - 22:36
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You shouldnt use different ISIS (tag), you can change ISIS level at both :

1- Interface level. command (isis circuit-type level-2)

2- ISIS routing protocol level. command (IS-Type level-2 only) which is not desired in your case.



mark_4728 Mon, 11/10/2008 - 23:33
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Thanks for your reply what abt dirrent area in one instance??? cuz main stuff is that loopback of two routers should be put in different area while there ethrnets will be in different area how we achieve that with running one instance....waiting for your reply

Mohamed Sobair Mon, 11/10/2008 - 23:48
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I donnt think I understood your question correctly..

I meant the ISIS tag not different areas,

As long as there is connectivity between A & D and level-2 is enabled on the segment then Loopbacks can be in different areas and both routers will maintain seperate level-2 database.


Mohamed Sobair Mon, 11/10/2008 - 23:50
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Not Loopbacks On different Areas, I meant the ISIS could be different areas on both routers.


mheusing Tue, 11/11/2008 - 01:34
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It looks to me as there might be a misunderstanding of the area concept or NSAP address in ISIS. ISIS has -no- concept of interfaces being in a specific area. This is an OSPF concept not used in ISIS at all.

In ISIS a router (not an interface) gets an address and a whole router will be in an area. Note: an ISIS router can have more than one ISIS NSAP address and thus can be in more than one area. But this feature was mainly introduced to allow for migration scenarios. Again, this feature does not mean an interface coul be assigned to an area in ISIS.

The requirements of interfaces being in an ISIS area you describe cannot be fulfilled with ISIS. Please calm down and do not go nuts over a problem impossible to solve :-)

This brings me to a question: who came up with the impossible requirements and why?

With 4 routers involved I would assume having a single ISIS area would be preferable unless there are hidden requirements/issues to be solved.

Hope this helps! Please use the rating system.




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