Subject: [Isis-wg] Listing some other pseudonode in CSNP

From: Abhishek Verma <[email-masked]>
Date: Thu, 14 Oct 2004 20:01:42 +0530

Hi,

I have a doubt.

R1 --- R2 
          |----- R3

R1-R2 and R2-R3 are on different LANs.

R2 happens to be the DIS on both of them.

I see that when R2 sends its CSNPs to R1, it includes the pseudonode
LSP that it has generated for the LAN2 also in it. Will this not
confuse R1?

Say the sys ID of R2 is 0000.1010.1010

It will create a pseudonode LSP for both LANs, say
0000.1010.1010.01-00 and 0000.1010.1010.02-00 respectively.

I see 0000.1010.1010.02-00 listed in the CSNP that R2 sends to R1. Now
R1 doesnt have this LSP, as it holds relevance only in the other LAN.
What will R1 now do? Will it send a PSNP back to R2 requesting it?

If it does, then it will make no sense.

Am i missing something?

Regards,
Abhishek.

--
Class of 2004
Institute of Technology, BHU
Varanasi, India

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From: mike shand <[email-masked]>
Date: Thu, 14 Oct 2004 16:44:35 +0100

All LSPs (including pseudonode LSPs) are flooded everywhere. So R1 SHOULD 
have a copy, and if it finds it hasn't the normal operation of the update 
process will ensure that it gets one.

R1, actually needs the "other LAN's" pseudonode LSP in order to compute a 
path R1 P1 R2 P2 R3...., as do any routers which are upstream of R1.

         Mike

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From: Jeff Learman <[email-masked]>
Date: Thu, 14 Oct 2004 12:14:04 -0400

>>R1 doesnt have this LSP, as it holds relevance only in the other LAN.

All LSPs have relevance on all ISs in the subdomain (L1 area or L2
backbone).  That's how the connectivity graph is created on which
you run SPF.

Jeff

At 11:44 AM 10/14/2004, mike shand wrote:
>All LSPs (including pseudonode LSPs) are flooded everywhere. So R1 SHOULD have a copy, and if it finds it hasn't the normal operation of the update process will ensure that it gets one.
>
>R1, actually needs the "other LAN's" pseudonode LSP in order to compute a path R1 P1 R2 P2 R3...., as do any routers which are upstream of R1.
>
>        Mike
>

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From: Marc Binderberger <[email-masked]>
Date: Thu, 14 Oct 2004 22:04:24 +0200

Hello Abhishek,

> LSP that it has generated for the LAN2 also in it.

The CSNP lists all LSPs in the database of R2. That include the R2--R3 
LAN pseudonode as well.

>  Will this not confuse R1?

I hope it won't :-)
The DIS pseudonode ID is part of the LAN IIH packets (the LAN ID 
field). So all members of a particular LAN know the DIS from that. No 
way to get confused.

> R1 doesnt have this LSP, as it holds relevance only in the other LAN.

No relevance? For sure, it is needed to get connectivity to R3. With 
the pseudonodes the topology looks like:

R1 -- (R2.01) -- R2.00 -- (R2.02) -- R3

Without the R2.02 (your 0000.1010.1010.02-00) it wouldn't be possible 
to built the connected graph R1 -> R2 -> R3.

> What will R1 now do? Will it send a PSNP back to R2 requesting it?

Yes (assuming it hasn't received the first flooding of R2.02).

Regards, Marc
--
Marc Binderberger    <[email-masked]>