Subject: [pim] Why doesn't PIM-SM support Join/Prune Msg Fragmentaion?

From: "Guo Feng" <[email-masked]>
Date: Mon, 20 May 2002 11:51:06 +0800

Hi all,

Why doesn't PIM-SM support Join/Prune Msg Fragmentaion?

In draft-ietf-pim-sm-v2-new-05 4.10.5.2 it states:
"4.10.5.2.  Group Set Fragmentation
There is an exception with group sets that contain a (*,G) Join source
list entry. The group set expresses the routers interest in receiving
all traffic for the specified group on the shared tree and it MUST
include an (S,G,rpt) Prune source list entry for every source that the
router does not wish to receive. This list of (S,G,rpt) Prune source-
list entries MUST not be split in multiple messages.

If only N (S,G,rpt) Prune entries fit into a maximum-sized Join / Prune
message, but the router has more than N (S,G,rpt) Prunes to add, then
the router MUST choose to include the first N (numerically smallest in
network byte order) IP addresses."

        If J/P Msg supports Fragmentation like BSR msg, 
 the (S,G,rpt) prunes after the first N IP addresses ( metioned above) won't be dropped.

      Why the spec doesn't support this?       

Thanks in Advance
Feng
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From: Mark Handley <[email-masked]>
Date: Sun, 19 May 2002 21:14:28 -0700

>      Why the spec doesn't support this?       

The new spec doesn't support it because we needed to remain compatible
with RFC 2362.  

I don't know why RFC2362 didn't support it - perhaps because it was
envisaged that groups that are large enough for it to be an issue
would mostly comprise many low-rate sources, and you might as well
leave those on the RP tree rather than transition to the SPT for them
all.  

 - Mark

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From: Dino Farinacci <[email-masked]>
Date: Mon, 20 May 2002 09:14:02 -0700

>> leave those on the RP tree rather than transition to the SPT for them

    We assumed to use IP fragmentation in this case.

Dino