Subject: comment on 3-way handshake proposal

From: Jeff Learman <[email-masked]>
Date: Fri, 23 Jul 1999 12:35:18 -0400

The three-way handshake proposal should point out that
all of the deficiencies result from failure to follow
6.7.2, Required subnetwork guarantees for point-to-point
links.

Please correct me if I'm wrong, but I believe that the
problems identified in the proposal are all caused by
using Frame Relay or some other unreliable link protocol,
or else implementation problems whereby a router can
restart IS-IS without resetting the link connection.

Of course, the three-way handshake proposal adds value
because it is great to be able to operate the protocol
over an efficient, unreliable link layer protocol.

I recommend the following changes to the text for the Abstract,
from:

   The IS-IS routing protocol (ISO 10589) does not use a three-way
   handshake when establishing adjacencies on point-to-point media.
   This paper defines an backward-compatible extension to the protocol
   that provides for a three-way handshake.  It is fully interoperable
   with systems that do not support the extension.

to:

   The IS-IS routing protocol requires reliable protocols at the link
   layer for point-to-point links.  As a result, it does not use a three-
   way handshake when establishing adjacencies on point-to-point media.
   This paper defines an backward-compatible extension to the protocol
   that provides for a three-way handshake, and permits IS-IS to be
   operated over an unreliable link layer protocol such as Frame Relay
   or PPP.  It is fully interoperable with systems that do not support
   the extension.

In addition, text should be added for edits to section 6.7.2, indicating
the relaxed requirements for systems that implement the recommended
option.  I'm not sure just what these new relaxed requirements
should be.

Regards,
Jeff
____________________________________________________________________

  Jeff Learman                           Internet:     [email-masked]
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From: Dave Katz <[email-masked]>
Date: Fri, 23 Jul 1999 09:53:13 -0700 (PDT)

An interesting catch--in all the years I've been looking at this I never
noticed that it does in fact seem to require a reliable data link layer.

The amusing part is, of course, that *nobody* runs this over LAPB or
802.2/II (or even a simple sequencing protocol that would blow up if
there was ever an unexpected sequence number, which would be
sufficient), not even DEC in the old days, and that the requirement
for a reliable data link is utter overkill for anything except the
startup gotchas that are fixed here.

I'll give a nod to this issue in the abstract, though the "requirement"
has obviously been completely ignored because it is broken, and thus
the protocol is still broken.  One thing I don't want to do is to give
the impression that every implementation on the planet is broken for
using the wrong subnetwork technology.

The "proper fix" would be to require 802.2/II but I don't think we
want to go down that road...

--Dave

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   Regards,
   Jeff