Subject: PIM spec

From: Francis Arts <[email-masked]>
Date: Tue, 27 Mar 2001 17:30:46 +0200

Hello Bill,

After our discussion at the IETF meeting in Minneapolis I have reread
the PIM spec.

p.29 of the latest PIM spec (dated March 2) states the following:

> Conceptually, the Register Tunnel is an interface with a smaller MTU
> than the underlying IP interface towards the RP.  IP fragmentation on|

> packets forwarded on the Register Tunnel is performed based upon this
> smaller MTU.  The encapsulating DR may perform Path-MTU Discovery to
the
> RP to determine the effective MTU of the tunnel.

You explained me that the smaller MTU takes both the outer IP header and
the PIM register header into account. So the order of actions will be:
1st step: Fragment the multicast IP packet taking the outer IP header
and PIM register header overhead into account.
2nd step: Stick the outer IP header and the PIM register header in front
of each fragment.

Question: Could we add as a clarification the following explicit
statement to the text:
"The smaller MTU takes both the outer IP header and the PIM register
header overhead into account. So if a multicast IP packet is fragmented,
the outer IP header and PIM register header are present in every
fragment."

Kind regards,

    Francis.