Subject: Re: [Isis-wg] RE: Unknown Version/ Protocol ID Extension

From: Jeff Learman <[email-masked]>
Date: Mon, 15 Jul 2002 11:40:50 -0400

The most appropriate use for a version/protocol ID field is to
introduce a completely new version of the protocol (like IPV4 vs.
IPV6.)  Off the top of my head, best practice would be to discard
PDUs with an unrecognized VPID.  This is the behavior that would
be expected by an OSI conformance test.  Conformance tests haven't
been found to be very useful in practice, and I doubt much
conformance testing is going on for IP-based implementations.

An implementation should NOT assume it can understand any of the
rest of the packet if it does not recognize the VPID.  Doing so
would make the VPID even less useful for future work than it
already is.

Extensions to IS-IS have been done exclusively through the use of
defining new TLVs, given that the semantics for an unrecognized
TLV is to ignore it but propagate it.  This has proven to be a very
useful mechanism.

Regards,
Jeff

Note:  I do not work in IS-IS at Cisco, and my opinions may not reflect
those of my employer.

At 11:22 AM 7/15/2002, Chan, Chung Ming wrote:
>Hi,
>        I'm running a test on how an ISIS implementation handles different
>kinds of encoding errors.
>
>        One of such errors is unknown version number.
>
>Since the current Version/Protocol ID Extension and Version fields in the
>ISIS PDU fixed headers are set to one (1),
>so if an ISIS implementation receive a PDU with different values, how should
>the receiving ISIS router handle the PDU?
>
>Should it just ignores/discards the PDU or act on the PDU if somehow it can
>decode *some*/*most* of the information out?
>
>I've two implementations in the lab ignore/discard the PDU and one response
>to the received PDU.
>
>Please, advise!
>
>
>Thanks,
>
>
>C. Ming Chan
>
>_______________________________________________
>Isis-wg mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/isis-wg

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---

From: Tony Przygienda <[email-masked]>
Date: Mon, 15 Jul 2002 08:54:45 -0700

>conformance testing is going on for IP-based implementations.
Discard PDU, anything else is just asking for major trouble. Equivalent 
to someone
speaking italian to you (assuming you don't speak italian ;-)
and you trying to parse it as English. Some sounds may
be similar but your chance of having a meaningfull conversation is 
basically nil.

    -- tony