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Re: PMTU/DF issues
> From: Karen Seo <kseo@bbn.com>
> a) send the PMTU information to all 3 hosts. As you
> observed, H1 and H2 aren't the intended recipients
> for the PMTU information and won't know what to do
> with it.
This would be the wrong thing to do. Be conservative in what you send.
> b) hold the PMTU information until another too-big
> packet arrives and then use that packet and the PMTU
> information to construct a ICMP PMTU for the
> originating host (H0).
>
This is what is described in RFC-1853:
The router uses the ICMP messages it receives from the interior of a
tunnel to update the soft state information for that tunnel. When
subsequent datagrams arrive that would transit the tunnel, the router
checks the soft state for the tunnel. If the datagram would violate
the state of the tunnel (such as the MTU is greater than the tunnel
MTU when Don't Fragment is set), the router sends an appropriate ICMP
error message back to the originator, but also forwards the datagram
into the tunnel. Forwarding the datagram despite returning the error
message ensures that changes in tunnel state will be learned.
Rather than putting all of this into the Architecture document, I'd think
it would be more efficacious to update RFC-1853.
WSimpson@UMich.edu
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BSimpson@MorningStar.com
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