Subject: Re: PIM hello option DR priority

From: Fred Bauer <[email-masked]>
Date: Thu, 25 May 2000 13:01:09 -0700

Tom,

OK, that's what I thought. The new SM draft, draft-ietf-pim-v2-sm-01.txt,
rearranged the indicies. 18 is DR priority and 19 is Bidirectional PIM 
capable.

Cheers, Fred

>In message <[email-masked]> you write:
>>At Interop in Las Vegas this year I noticed that Junipers running
>>JunOS release 4.0 were sending PIM hello option 19 with a length
>>of 4 (Invalid Bidirectional PIM capable option). Presumably what
>>the coder was trying to do was specify DR priority, but was following
>>the older spec, draft-ietf-idmr-pimv2-dr-priority-00.txt. Has anyone
>>else seen similar behavior on this or other manufacturers' routers?
>>
>>By the way, if anyone from Juniper is listening, I imagine that
>>you'd like to fix this.
>>
>>Fred
>
>Actually, that code has been in there since the DR priority draft came
>out and is the same in all JUNOS releases shipping for the past few
>years.
>
>So was the DR priority draft wrong because the option was already
>used or did the option get re-assigned?
>
>Thanks,
>Tom

---

From: Bill Fenner <[email-masked]>
Date: Thu, 25 May 2000 13:20:33 -0700

The PIM Hello option ID space got renumbered.  It's very unclear who chose
to do this and why, and what consideration was given to compatibility
issues.

rfc 2117					 6/1997		n/a
draft-ietf-idmr-pimv2-dr-priority-00.txt:	 3/1998		DR-prio: 19
rfc 2362					 6/1998		n/a
draft-farinacci-bidir-pim-01.txt:*		 5/1999		bidir: 19
draft-ietf-pim-v2-dm-03.txt:			 6/1999		n/a
draft-ietf-pim-v2-sm-00.txt:			10/1999		DR-prio: 18
draft-ietf-pim-v2-sm-01.txt:			11/1999		DR-prio: 18

I don't know what fix to propose; it'd be nice if we could standardize
on 19 since otherwise early adopters get screwed, but obviously then
there are compatibility issues with more recent implementations.  Sigh.

  Bill

* - ironically, draft-farinacci-bidir-pim-01.txt contains a reference to
    draft-ietf-idmr-pimv2-dr-priority-00.txt

---

From: Desikan Saravanan <[email-masked]>
Date: Thu, 25 May 2000 17:38:02 -0700

I Agree with Fred. Option 3 is the best among all.

Des

-----Original Message-----
From: Fred Bauer [mailto:[email-masked]]
Sent: Thursday, May 25, 2000 4:49 PM
To: [email-masked]
Cc: [email-masked]; [email-masked]; [email-masked]
Subject: Re: PIM hello option DR priority 

Liming,

My 2 cents worth is that option 3 makes the most sense given that
routers out there already honor DR-priority = 19. I am guessing 
that bidir is not yet widely established, so the impact will be
minimal.

Fred

>Sigh, this was due to the code assignment conflict with other options.
>It was discovered only later when the drafts were consolidated. I
>thought I was the only coder who implemented the DR priority option at
>that time, and it would only involve myself if I changed it..
>
>It was an oversight that this was not included in the "significant
>changes" section of the later PIM-SM draft, since we were only doing
>diffs against a previous RFC, not against the previous
>Internet-Drafts...
>
>It could have been worse, but the positive side of this is that the DR
>election mechanism is robust enough to not cause havoc. If not all
>neighbors are DR-priority capable, they will drop down to the old
>address-comparison-only mode, and DR-priority will become active again
>when the "non-capable" neighbors all disappear.
>
>It is hard to guess how much deployment has been done with
>the DR election priority option and the Bi-dir option. I can
>think of the following few options to move forward:
>
> 1) Deprecate both values of 19 and 18 as valid Hello options.
>    Assign new values to both DR-prio and Bi-Dir options. Everyone
>    needs to switch;
>
> 2) Keep the current PIM-SM option value assignment, and let those
>    who implemented draft-ietf-idmr-pimv2-dr-priority-00.txt
>    change their code;
>
> 3) Deprecate the current Bi-Dir option code 19, making it the
>    DR priority election priority code again. Make code 18 an
>    invalid option, and reassign a new code for Bi-Dir option
>
>    This probably is acceptable if Bi-dir PIM is not widely
>    deployed yet. But I will understand if people don't want to
>    say so here.
>
> Comments ?
>
>-Liming
>
>
>> Date: Thu, 25 May 2000 12:27:17 -0700
>> From: Tom Pusateri <[email-masked]>
>>

---

From: "Shekhar, Ravi" <[email-masked]>
Date: Fri, 26 May 2000 10:55:29 -0400

>     invalid option, and reassign a new code for Bi-Dir option

   Additionally, it might be worth pointing out that the new implementations

   can still interoperate with existing implementations by looking at the 
   option-length field. Its 4 for DR-priority and 0 for Bidirectional PIM.

   - Ravi Shekhar.

---

From: Fred Bauer <[email-masked]>
Date: Fri, 26 May 2000 10:32:27 -0700

>option-length field. Its 4 for DR-priority and 0 for Bidirectional PIM.

Ravi's pointed out the obvious workaround since the (option,length) pair
gives enough information to comply with the old and new indicies for
DR priority.

option   length  interpretation
------------------------------------------------------------------------
  18       0       invalid
  18       4       DR priority
  19       0       Bidir
  19       4       DR priority

This is what we've done for now until the spec is clarified.

Thanks, Fred