Subject: Re: [RRG] draft-rja-ilnp-intro-01.txt

From: Christian Vogt <[email-masked]>
Date: Wed, 6 Aug 2008 12:25:30 +0300

Brian and Tony -

>> The ONLY thing that causes MTU issues is encapsulation approaches.
>
> Adding optional headers (as in shim6) shortens the upper layer payload
> for a given link MTU, and that is a problem if the upper layer doesn't
> know about it.

Agree, and FWIW: The same happens with Mobile IPv6 route optimization
options, at least in FreeBSD.

Anyway, this problem is just an implementation issue.  It is easy to
fix if the packet extension happens inside the sending host, where
sufficient information is available to compute correct packet sizes.
  OTOH, if packets are extended in the network, it is harder to get
hosts to size their packets correctly.  It is still doable if the
packet extension happens within the administrative domain of the
sending host, because a reduced MTU could then be communicated to
hosts via configuration messages, such as IPv6 Router Advertisement
messages.  The problem becomes harder if the packet extension happens
outside the sending host's network, such as in proxy solutions.

- Christian

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