From: Chris Lewis \(chrlewis\) (chrlewis@cisco.com)
Date: Sat Jun 25 2005 - 15:46:50 GMT-3
One of the lesser known configurations for ISIS has you configure
multiple NET values under the router isis section.
This is not a good practice, and only really has application in
migration scenarios, but it is posible to configure up to 3 distinct NET
values. If you do that, you have freedom to have two ISIS areas on the
one router and have each of them as level 1, level2 or any combination
thereof.
Here's an example
R5-----------R3----------R1
S3/0 S4/0 E0/0 E0/0
R3 has the following configuration
Router isis
Net 49.0001.0000.0000.0003.00
Net 49.0002.0000.0000.0003.00
Int s4/0
Ip router isis
Int e0/0
Ip router isis
R5 has the following configuration
Router isis
Net 49.0001.0000.0000.0005.00
Int s3/0
Ip router isis
R1 has the following
Router isis
Net 49.0002.0000.0000.0001.00
Int e0/0
Ip router isis
Now if you look at the following to see what happens by default:
R3#sho clns nei
System Id Interface SNPA State Holdtime Type
Protocol
Router1 Et0/0 aabb.cc00.a800 Up 28 L1L2
IS-IS
Router5 Se4/0 *HDLC* Up 24 L1L2
IS-IS
Now make R1 and R5 only able to establish L1 adjacencies with the
is-type level-1 in the router isis configuration.
R3#sho clns nei
System Id Interface SNPA State Holdtime Type
Protocol
Router5 Se4/0 *HDLC* Up 27 L1
IS-IS
Router1 Et0/0 aabb.cc00.a800 Up 22 L1
IS-IS
So R1 and R5 are in different areas, and R3 forms a Level 1 relationship
with both of them and routes can be passed.
Cheers
Chris
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
John Matus
Sent: Saturday, June 25, 2005 12:47 PM
To: lab
Subject: isis adjacencies
just trying to make sense of some things i've noticed with isis i know
that level-1 areas act like stub areas, and level-2 areas act like
transit areas.
question 1: should you be able to ping from a level 2 area to a level
1
router, if that router is NOT directly connected? e.g.- not a level-1-2
router.
question 2: if you have a router that belongs to 2 areas, does that
mean that the router must be a level-1-2 or at least a level-2? i seem
to remember an IE lab where there was a router <R6> that had a level-1
adjaceny to BB1 and a
level-1-2 adjaceny to another router. is it possible for a router to
have 2
level-1 adjacenies to two different networks (and still pas on routing
updates between them)? this lab i'm talking about had:
BB1-----level-1 areaY--------R6--------level-2--areaZ-----------R3----
and it was able to pass the routes from bb1 to r3 <if i remember at all
correctly>
just trying to get my facts straight.
Regards,
John D. Matus
MCSE, CCNP
Office: 818-782-2061
Cell: 818-430-8372
jmatus@pacbell.net
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