Subject: [Isis-wg] Concerns with 3-way-handshake

From: "Philip Christian" <[email-masked]>
Date: Tue, 4 Dec 2001 17:04:05 -0000

I have a number of concerns and comments about the 3-way-handshake draft,
draft-ietf-isis-3way-03.txt. I'm sure I remember hearing that this draft is
about to become an RFC, although I can find no evidence of this on the RFC
editor's web page.

Here are my concerns.

This draft specifically declares itself to be useful in SONET networks
(presumably in the embedded DCC channels, although this is not stated).
However I believe that there is an area of ambiguity in it which reduces its
usefulness somewhat. The draft mentions only IIH packets, where as SONET and
SDH networks (oh yes, SDH is not mentioned either) are currently based on
CLNS and therefore the NEs transmit ISH packets too.

I understand that an old CLNS SONET/SDH node will not support three-way
handshaking anyway, and so a new neighbour would engage legacy mode anyway,
BUT....

With the advent of G.7712 vendors will be looking at implementing dual IP
and CLNS routers that are able to still interface to the old CLNS nodes, and
which also support three way handshaking. Such a new dual node may well need
to declare itself a CLNS End System, and so will be transmitting ISHs. This
will be necessary to terminate RFC 3147 encapsulated packets, for example.

The problem is that I believe that receipt of ISH packets "short circuits"
the three way handshake, and results in the adjacency coming up whether the
neighbour has received  IIHs, or not. This is my understanding of the
problem:
A is connected to B and issues an ISH.
B receives the ISH, and according to ISO 10589 section 8.2.2 creates an
adjacency of type "Initialising".
B now reports to A in the new "Point to point adjacency state" option that
the adjacency is "Initialising".
A receives this and according to the table in the draft, brings the
adjacency "up".
However B may never have received an IIH from A and so the three way
handshake has been short circuited, or have I misunderstood something?

The draft really needs to state how a router with three way handshaking
should handle receipt of an ISH from a neighbouring IS that also supports
the option.

I guess that this is not a problem for pure IP routers if they ignore ISHs,
and this could be stated.

Next concern; what happened to ISHs anyway? RFC 1195 states in section 4.4
"For point-to-point links, IS-IS requires exchange of ISO 9542 ISHs, as the
first step in establishing the link between routers. All IS-IS routers are
therefore required to transmit and receive ISO 9542 ISH packets on
point-to-point links.". There is a similar statement in section 5.1.

I am told that many implementors do not transmit ISH packets anymore, as
they cannot terminate CLNP and thus are not an CLNS End System anymore.

This seems perfectly logical to me, but, if this is the case then I think
that this draft should state it. It is the after-all going to be (hopefully)
the first RFC to actually alter the adjacency creation process from ISO
10589; RFC 1195 did not change it. If it is now okay not to transmit ISHs
then let's say so.

I think that this issues could be addressed just in a few sentences, once we
have agreed how to handle ISHs on nodes that need to. I am ready to help
with some drafting in order to help get this right.

Regards, Philip Christian.