Subject: RE: [Isis-wg] Doubt

From: selvarajR <[email-masked]>
Date: Thu, 14 Sep 2000 15:29:12 +0530

>this actually will be worse, the IS-1 and IS-2 may randomly setup
>adjacnecies with IS-3 on either c3 or c4 depends on the timing. since
>they will rejects the second adjacency setup due to conflict in systemID
>and mac addresses.

Yes that is possible if  c1 and c2 already exist on the network before c3 
or c4.
For instance if another IS , IS-4, be commimg up then there is no gaurentee 
that IS-4 also will form the same adjacency with IS-3 as IS-1 & IS-2.

Selva
-----Original Message-----
From:	Naiming Shen [SMTP:[email-masked]]
Sent:	Tuesday, September 12, 2000 1:04 PM
To:	[email-masked]
Cc:	'ISISWG'
Subject:	Re: [Isis-wg] Doubt

 ]
 ]          IS - 1                              IS - 2
 ]             |                                      |
 ]             | c1                                  | c2
 ]-----------------------------------------------------------
 ]                   c3 |     | c4
 ]                        |     |
 ]                        |     |
 ]                         IS - 3
 ]
 ]For the above broadcast topology  let,
 ]   IS-1, IS-2 & IS-3 be three L1 intermediate  systems
 ]   c1, c2, c3, c4 be the respective IS's circuits. where c4 be the back 
up
 ]link for IS-3.
 ]   Let priority of c1 be 10, c2 be 20, c3 be 30 and c4 be 40.
 ]
 ]Here, IS -1  and IS -2 will have two  adjacencies for  IS -3 with same s 
 ]ystem Id but, different SNPA.
 ]But, IS -3 won't have any adjacency of it's own. ie c4 is not known to c3 
 ]and vice versa
 ]
 ]DOUBTS:
 ]1. After DR election c1 , c2 and c4 will say c4 as the DR. But c3 will 
say
 ] c3 as the DR. So the  LAN will have more than on DR at a time

this actually will be worse, the IS-1 and IS-2 may randomly setup
adjacnecies with IS-3 on either c3 or c4 depends on the timing. since
they will rejects the second adjacency setup due to conflict in systemID
and mac addresses.

 ]2. If  the IS won't have two interfaces on the same LAN as in the above
 ]topology , then why do we need to check for system ID and SNPA. for
 ]creating new adjacency over a circuit.   I feel checking for System ID
 ]alone sufficient. So we can discard duplicate IIH.

i guess the idea was to prevent accident. if you want to bring a new
router into the LAN and misconfigure the systemID which duplicates the
one already in operation, the proper behaviour should be the new router
can not join the ISIS on this LAN instead of knocking off the one already
working. since the chances are the new router probably is configured wrong.
so this check on both systemID and mac address is useful.

 ]
 ]Pls  correct me , if  I'm wrong.
 ]

- Naiming

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