Subject: [pim] Unknown Pim Hello options

From: Greg Schwendimann <[email-masked]>
Date: Thu, 17 Jun 2004 12:35:29 -0400

Hello,
	I have read the pim spec but cannot find out what a router should do
with an unknown pim hello option.  The spec says I may ignore the
option.  Does that mean the routers should become neighbors or ignore
each others hello messages?

Thanks
Greg

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From: Tom Pusateri <[email-masked]>
Date: Wed, 23 Jun 2004 12:12:06 -0700

I would log the option and then ignore it.
You should still treat the sender as a neighbor.

Tom

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From: Pavlin Radoslavov <[email-masked]>
Date: Wed, 23 Jun 2004 17:29:14 -0700

> each others hello messages?

I believe the answer is that if one of the routers includes a Hello
option that the other router(s) don't understand, but the rest of
the message is fine (e.g., it contains the HoldTime option, etc),
then the routers still should become neighbors.

If you have several PIM routers on a LAN and some of them ignore
each other's Hello messages, bad things can happen. E.g., the PIM
Assert messages will be rejected with all negative result of that
(duplicate traffic, etc).

Indeed, the spec doesn't say explicitly that the routers still
should be neighbors, so I'd be interested to know if other people
have different interpretations.

Pavlin

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From: Christopher Thomas Brown <[email-masked]>
Date: Thu, 24 Jun 2004 11:16:34 -0400

On Thu, 17 Jun 2004 12:35:29 EDT
>each others hello messages?

It means the option may be ignored. If an implementation does ignore
such options then yes they would become neighbors. If an implementation
does not ignore such options then it depends on what it does do (eg
drop or log or ???).

Chris

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From: John Zwiebel <[email-masked]>
Date: Thu, 24 Jun 2004 12:53:43 -0700

> have different interpretations.

2cents

Yes, still become neighbors, but let's say that one of
the routers on the LAN does not support bi-dir (as
an example) then none of the routers on the LAN should
do bi-dir.

There is no 'hello-ack' so its possible to have
asymmetrical neighborliness ;-)  A prescription for
disaster.

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From: David Lamparter <[email-masked]>
Date: Sun, 27 Jun 2004 15:57:16 +0200

1 euro-cent...

The "right thing to do" would be to have ignoring unknown Hello Options
be a MUST and require logging of this (once per neighbor and GenID).
Things will end up with a bulkload of compatibility configuration
options on more advanced PIM routers otherwise, which, in turn, SHOULD
of course log what they do on noticing some neighbors don't support
extension abc.

Specifications for extensions on their side should state what to do on
receiving Hellos not indicating support for the specified extension.
(for example, bidir should state "if a hello without Bidir-Capable
option is received, bidir has to be disabled on the interface..."; other
extensions [popcount, nnhop, ...] may add rules for interaction with
unsupporting routers)

There really is no "hello-ack", but there are the other router's hellos
with some options present and some options not present.

David

P.S.: in case it got lost in my bad english, I meant to say "change the
draft, make ignore a MUST"