Subject: IPv6 PTMU query

From: vijay <[email-masked]>
Date: Tue, 24 Apr 2007 17:39:26 +0530

Hi All,

       I am currently analyzing the IPv6 path MTU.

As the IPv6 path MTU calculation is done by error correction method, I was
thinking of suggesting a

proposal for calculating the path MTU optimally. I am interested in knowing
if the path MTU is a problem 

in real networks and how often packets are dropped due to MTU too small, in
real networks? 

       If there is some information regarding the same, please share it.

Regards

Vijay

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From: Remi Denis-Courmont <[email-masked]>
Date: Tue, 24 Apr 2007 15:12:01 +0200

On Tue, 24 Apr 2007 17:39:26 +0530, vijay <[email-masked]> wrote:
> I am interested in knowing if the path MTU is a problem in real networks

Yes it is. Some people have a 1492 MTU due to PPP encapsulation; some have
9000+ such a gigabit links. And in IPv6 case, 1480 (and 1472) are fairly
common because of IPv6 over IPv4 tunnels.

> and how often packets are dropped due to MTU too small,

It very much depends on the network topology. But it definitely happens in
various cases.

--
Rémi Denis-Courmont
http://www.remlab.net/

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From: Mark Smith <[email-masked]>
Date: Thu, 26 Apr 2007 20:54:23 +0930

Hi Vijay,

On Tue, 24 Apr 2007 17:39:26 +0530

>        If there is some information regarding the same, please share it.

Just in case you aren't aware of it, a recent RFC specifies a mechanism
to use probing of Path MTUs via different sizes of packets rather than
ICMP error feedback :

"RFC4821 - Packetization Layer Path MTU Discovery"

There is also an implementation of this in fairly recent Linux kernels.

HTH,
Mark.