Subject: [pim] draft-ietf-pim-sm-bsr-02

From: David Barnett <[email-masked]>
Date: Fri, 10 May 2002 12:36:43 -0400

Hello,
I have a concern with respect to draft-ietf-pim-sm-bsr-02.

In the spec it states:
"Every C-RP periodically unicasts a C-RP-Adv to the BSR for that scope
zone to inform the BSR of the C-RP's willingness to function as an RP.
Unless configured otherwise, it does this for every Admin Scope zone for
which it has state, and for the global scope zone." 

What is the purpose behind allowing a C-RP for a group to advertise itself 
to the global scope zone BSR once it knows there is a scope zone for the 
group?    

Routers on the other side of the scope zone boundary will be unable to
use the C-RP as the RP for the group, yet they will try to do so (depending
on priorities etc). In other words, group traffic is blackholed in
any other region.

Is this the intention of the design?

Thanks for your time,
-David Barnett

P.S. It appears that the mailing list archive at 
ftp://catarina.usc.edu/pub/pim/mail-archive/pim/  is down. Is there another 
archive?
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From: Mark Handley <[email-masked]>
Date: Fri, 10 May 2002 10:28:30 -0700

>Is this the intention of the design?

Say there are two scopes, global and scope A.  By default, a C-RP
might be a C-RP for both.  It sends a C-RP-advertisement message to
the global scope BSR advertising it's candidacy to be a global scope
RP, and it also sends a C-RP-adv message to the scope A BSR
advertising it's candidacy to be a scope A RP.  The former message
lists the global scope address range, and the latter message lists the
scope A address range.

Given that global scope and scope A address ranges don't overlap,
what's the problem here?

Cheers,
	Mark

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From: Mark Handley <[email-masked]>
Date: Fri, 10 May 2002 10:41:46 -0700

>The problem is no joins on the other side of the boundary will ever reach the
>rp. 

But the RP for scope A and the BSR for scope A are on the same side of
the boundary for scope A.  Otherwise how would the RP have heard about
the scope? Remember that BSMs for scope A can't cross the boundary
either.

Cheers,
	Mark

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From: David Barnett <[email-masked]>
Date: Fri, 10 May 2002 13:37:49 -0400

According to draft-ietf-pim-sm-bsr-02:
"Admin scope zone boundaries must be configured at the Zone Border
Routers (ZBRs), as they need to filter PIM Join messages that might
inadvertently cross the border due to error conditions."

If no pim joins are allowed to cross the boundary then data would never flow
down from the RP correct?

If so then why bother announcing the C-RP to the global BSR.

Thanks,
-David Barnett

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From: Pavlin Radoslavov <[email-masked]>
Date: Fri, 10 May 2002 10:56:49 -0700

> ftp://catarina.usc.edu/pub/pim/mail-archive/pim/  is down. Is there another 

The FTP site on catarina.usc.edu is not operational anymore. The
valid archive URLs are available from the PIM homepage
(http://netweb.usc.edu/pim/):

The mailing lists archive is available from
http://netweb.usc.edu/pim/mail-archive/
An archive for the traffic since January 2002 is available from
http://netweb.usc.edu/pipermail/pim/

Regards,
Pavlin

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From: David Barnett <[email-masked]>
Date: Wed, 15 May 2002 13:34:55 -0400

Let me state my understanding of the specs and see if what I say is
correct.

RFC 2365 constrains the topologies of scoped regions in that a region must
be connected, convex and if two regions intersect the outermost region's
scoped group address range cannot include the innermost region's address
range.

So if I have two scoped regions A and B, where B is topologically contained
within A. Then the group range for A cannot include the group range of B.
So for example if B is the group range 239.0.1.128/26 then A could not
be the full group range 239.0.1.0/24 but could instead be
239.0.1.0/24 - 239.0.1.128/26 (by configuring multiple scopes to cover
the allowed portions of that range).

If this understanding is correct, then should a ZBR try to compensate
(by filtering BSMs) in the case where region A is misconfigured. So,
for example, if region A is configured as 239.0.1.0/24 and B is
239.0.1.128/26. It seems that the ZBRs that define the boundry for
region B could filter A's BSMs. If they do not filter then nodes in region
B may try to use an RP in region A for groups within B's group range.
If they do filter then nodes in region B will not have an RP for the
legitimate groups of A. Which situation is 'worse'?

The next question is about compatibility with the older BSR spec. Is
the 'global scope' BSR really only BSR for the group range 224.0.1.0 -
238.255.255.255? Implemenations of the older spec don't have this
limitation. One would like this spec to act like the older spec
in the case where there are no actual scope regions defined (ie
accepting and including in the BSR message CRP-Advs for all group ranges).
But this doesn't seem possible for correct operation. Is it correct
that the global scope BSR should only accept and include CRP group
ranges fitting in 224.0.1.0 - 238.255.255.255?

Thanks for your time,
-Dave

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From: Mark Handley <[email-masked]>
Date: Wed, 15 May 2002 10:53:09 -0700

>legitimate groups of A. Which situation is 'worse'?

I don't think that they should filter, but they should log a
misconfiguration error.  In general, I don't think routers should try
and fix up broken configurations, but they should definitely report
them.

>ranges fitting in 224.0.1.0 - 238.255.255.255?

This is an interesting topic for debate.  What really is global scope
for ASM?  Presumably it should also exclude 232.0.0.0/8?

This is a very confused area for many historic reasons.  Personally I
don't think it would be unreasonable for a BSM to list 224.0.0.0/4, so
long as global scope address allocators know to stay clear of 239/8
and 232/8.  This of course means that you wouldn't log a warning at a
ZBR if you see such a global scope advertisement.  But I'd like to
hear other people's opinions on this.

Cheers,
	Mark