From: Tom Martin (tig@wiltecinc.com)
Date: Fri Jul 23 2004 - 23:54:31 GMT-3
Wang,
Both methods will work, but work slightly different. Having multiple
nets configured will allow L1 adjacencies to form for any of the
configured nets. If the lab requirements indicate that adjacencies
should form for only a given net, then that's not the right way. :)
Having multiple ISIS areas (configured just like OSPF processes but with
name identifiers instead of numbers) allows you to specify certain NETs
for certain areas. The L2 ISIS area (by default the first ISIS area
configured) will automatically learn L1 route from all of the configured
L1 areas, redistribution isn't necessary. L1 areas won't learn L2 routes
or routes from other L1 areas, but they'll have the ATT-bit set if
multiple areas are configured. Cisco routers will even set the ATT-bit
if there isn't a L2 area, configure 2 L1 areas and the ATT-bit will get
set in both. But if Cisco says that no default routing may be used, then
that's not the right way... (Note that you can redistribute between L1
areas or route-leak, but again it depends on the lab requirements and
what hoops you are given to jump through).
I probably went into way more detail than you needed to answer your
question, but hopefully the explanation will help others too. And your
answer, like the answer to most questions here is: It depends. Know
every single way of doing it and the nuances of each and you'll do fine.
:)
-- Tom
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Wang Dehong-DWANG1
Sent: Friday, July 23, 2004 4:37 PM
To: ccielab@groupstudy.com
Subject: ISIS mutiple area question..
I have another question for the group. If you are asked to configure
multiple areas, say 2, under one router, should you configure two net
statements under one router isis or two seperate net statements under
different router isis? or it doesn't matter? My thought is two router
isis statements, but I did see case 1 as well, so I would like to
clarify it with the group..
Case 1:
router isis
net 49.area-A.xxxx.xxxx.xxxx.00
net 49.area-B.xxxx.xxxx.xxxx.00
Case 2:
router isis
net 49.area-A.xxxx.xxxx.xxxx.00
router isis area-b
net 49.area-B.xxxx.xxxx.xxxx.00
thanks in advance..
- Dehong
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