Subject: RE: [Isis-wg] Routing or forwarding

From: Jeff Parker <[email-masked]>
Date: Fri, 10 Aug 2001 10:07:37 -0400

> ps: Though I don't think the spec has anything against ISIS 
> running over IP, but I doubt if there are any such 
> implementations on the field.

A bit of history on this...

There -was- a draft proposal to run ISIS over IP.  A number
of reasons were put forward for this, including allowing
larger LSPs (let IP handle fragmentation) and avoiding 
something refered to as the "ATM cell tax" that came about
if you needed to multiplex two protocols over ATM, and the
resulting effect of requiring two ATM cells to hols a TCP 
Ack.  There were folks who implemented this encapsulation.  

The chief driving force for seemed to be avoiding
the cell tax: there were doubts that adding a second
layer of fragmentation was a good thing.  

An alternative proposal to deal with the cell tax was
proposed which encodes both IP and ISIS traffic "raw",
and demultiplexes based on the difference between
the first nibble of the NLPID for ISIS (0x8) and 
the version number for IP (0x4 or 0x6).  This proposal
seems to have aged off the list, but gathered support
from several vendors.  

- jeff parker
- axiowave networks
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From: Henk Smit <[email-masked]>
Date: Mon, 20 Aug 2001 15:46:57 -0700 (PDT)

> seems to have aged off the list, but gathered support

  I wrote the draft for that proposal when I was at a previous job.
 At the time I contacted a few large ISPs that had ATM backbones.
 Nobody seemed to be really interested to save some bandwidth.
 Some because they had enough bandwidth, some because they were
 planning to move to PacketOverSonet (and MPLS).
 So I never commited the changes to my former employer's software.
 And because my idea had no been deployed, I let the draft die.

  Are there really people using this hack to run ISIS and IP over
 one aal5mux VC ? I'd be very interested to hear from them.
 Thanks,

    Henk.