Subject: Fragmentation

From: Francis Arts <[email-masked]>
Date: Sat, 10 Feb 2001 12:43:47 +0100

Hello,

I have a question on fragmentation being applied in the source DR /
PMBR.

Consider a multicast IP packet that needs to be sent in a PIM-SM
register message from the source DR / PMBR to the RP. If
fragmentation is required, 2 approaches are possible to execute this
fragmentation operation (the 2 possibilities are listed next).
Which one of these 2 approaches is the correct one to use?

Approach 1
========

FIRST do fragmentation of the multicast IP packet
THEN stick the PIM-SM register header and the unicast IP header on every
fragment of the multicast packet.

==> Consequence: The unicast IP header, the PIM-SM register header and
the multicast IP header are present in EVERY fragment.
Therefore, reassembly is NOT needed in the RP. Every fragment can be
handled independently in the RP and every fragment can
travel independently through the Internet (after stripping the unicast
IP header and the PIM-SM register header).

Approach 2
========
FIRST stick the PIM-SM register header and the unicast IP header on the
multicast packet.
THEN do fragmentation on this packet (this packet consists of a unicast
IP header, PIM-SM register header and multicast IP header
+ payload)

==> Consequence: The PIM-SM register header and the multicast IP header
are NOT present in every fragment. Therefore,
reassembly is needed in the RP. After reassembly the reassembled packet
can be handled in the RP and can travel further through the
Internet.

Sorry if this issue has already been discussed in the working group
before. If this would be the case, can you then give me a pointer to the
corresponding thread?

Thanx.

Kind regards,

    Francis.