Subject: RE: [Isis-wg] Proprietary / Private TLV numbers?

From: "Philip Christian" <[email-masked]>
Date: Fri, 12 Jul 2002 15:50:01 +0100

"Therefore an IS SHOULD NOT regularly transmit information in a 
proprietary TLV in an LSP"

I think that this might work better as
"Therefore an IS SHOULD NOT frequently transmit information in a 
proprietary TLV in an LSP"

Philip

-----Original Message-----
From: Christian, Philip [HAL02:GI50:EXCH] 
Sent: Friday, July 12, 2002 3:43 PM
To: 'mike shand'; Jeff Learman
Cc: [email-masked]
Subject: RE: [Isis-wg] Proprietary / Private TLV numbers?

This is my first thought on the problem of abuse of LSPs.  As normal 
I've probably written too much, but it will give you guys something 
to chew on and improve.  Comments? 
Philip 
Appropriate use of proprietary TLVs. 
   IS-IS is a highly scalable routing protocol.  Networks have been 
   deployed containing many hundreds of ISs in a single level-1 area or 
   level-2 subdomain. 
   One contributing factor to this scalability is that an IS needs to 
   advertise its links and metrics only when it starts up, or when its 
   local connectivity changes in some way.  In this way the amount of 
   routing information traversing an IS-IS routed network is normally 
   very low.  Unlike some other routing protocols, there is no periodic 
   transmission of routing information, except for LSP timeout which is 
   very infrequent. 
   A downside of this is that every time one IS does advertise a new 
   state of connectivity, every single IS in the network will need to 
   recalculate all of its routes, although there are certain 
   optimisations that reduce this load. 
   An unfortunate consequence of an IS sending out new information in a 
   proprietary TLV in an LSP is that it causes every other IS in the 
   level-1 area or level-2 subdomain to recalculate all of its routes, 
   whether an IS understands that particular TLV or not.  If many ISs 
   in a large network were to frequently send out new LSPs then all of 
   the ISs might spend most of their time recalculating routes, which 
   would reduce scalability and stability considerably. 
   Therefore an IS SHOULD NOT regularly transmit information in a 
   proprietary TLV in an LSP.  Proprietary TLVs in LSPs SHOULD NOT be 
   used except for the following (or similar) purposes:- 
   1. For information about an IS that is constant or very rarely 
      changed. 
   2. For information that is related to topology, in which case the 
      topology change would result in a new LSP anyway.  In this case 
      the topology change SHOULD trigger the proprietary TLV to be 
      updated at the same time as the normal LSP update.  This results 
      in all of the other ISs in the network performing only one SPF run 
      rather than two. 
   Proprietary TLVs in LSPs MUST NOT be used as a generalised 
   communication channel. 
   Proprietary TLVs that are used in Hello and SNP PDUs are not flooded 
   throughout a network, and do not result in route recalculations 
   (unless they are part of a feature that enables or disables 
   adjacencies).  Therefore the proprietary TLV MAY be used more freely 
   in Hello and SNP PDUs.

---

From: Mike Truskowski <[email-masked]>
Date: Fri, 12 Jul 2002 08:35:38 -0700 (PDT)

No, I don't agree with this.  How can you say you have a private
TLV and then to say don't use it often?  Nonsense.  Don't placate.

Mike

Philip

-----Original Message-----
From: Christian, Philip [HAL02:GI50:EXCH] 
Sent: Friday, July 12, 2002 3:43 PM
To: 'mike shand'; Jeff Learman
Cc: [email-masked]
Subject: RE: [Isis-wg] Proprietary / Private TLV numbers?

Philip

-----Original Message-----

Cc: [email-masked]

Philip

level-2 subdomain.

very infrequent.

changed.

rather than two.

communication channel.

in Hello and SNP PDUs.