Subject: Re: UDP path MTU discovery

From: Andi Kleen <[email-masked]>
Date: Sun, 28 Mar 2010 10:41:37 +0200

David Miller <[email-masked]> writes:

> From: Glen Turner <[email-masked]>
> Date: Fri, 26 Mar 2010 10:32:31 +1030
>
>> This differs from TCP, where it is the kernel -- and not
>> the application -- which organises retransmission. On
>> receiving a ICMP Fragmentation Needed the kernel can
>> immediately re-probe the path MTU wiht no waiting for
>> an exponential timer to expire.
>
> So the argument is, the kernel TCP does retransmission smart,
> userspace UDP apps do it stupidly, so let's turn off the feature
> instead of fixing userspace.
>
> Right?
>
> Sorry, fix this correctly in the user apps.  Putting the
> blame on UDP path MTU discovery is placing it in the
> wrong spot.

It means though that all IPv6 UDP applications essentially have
to implement path mtu discovery support (which is non trivial) 

Will be likely a long time until they're all fixed.

Seems like a big hole not considered by the IPv6 designers?

-Andi
-- 
[email-masked] -- Speaking for myself only.