Message-ID: <53D803BE.1040500@...1926...>
Date: Tue, 29 Jul 2014 22:27:42 +0200
From: Julien Muchembled <jm@...1926...>
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Subject: Re: [Openvpn-devel] [PATCH] Fix --mtu-disc option with IPv6
	transport
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To: Gert Doering <gert@...1296...>
Cc: openvpn-devel@lists.sourceforge.net

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Le 07/29/14 20:57, Gert Doering a =E9crit :
> On Tue, Jul 29, 2014 at 07:28:49PM +0200, Julien Muchembled wrote:
>> Socket configuration of MTU discovery was done unconditionally at IP lev=
el,
>> which has no effect for other protocols. This fixes the issue of OpenVPN
>> sending fragmented tcp6/udp6 packets even when 'mtu-disc yes' option is =
passed.
>=20
> Sounds good.  I'm not sure I understand what that socket option *does*,
> though...  will it make the kernel report back any ICMP packet too big
> messages received?  Or will it not honour those unless IPV6_MTU_DISCOVER
> is set?
>=20
> Is there documentation for that socket option somewhere?

'man 7 ip' and 'man 7 ipv6'

For example:
  A --[mtu=3D1500]-- B --[mtu=3D1400]-- C

Given a UDP6 socket on A with IPV6_MTU_DISCOVER=3DIP_PMTUDISC_DO,
    sendto(1452 bytes, B) will succeed
but sendto(1452 bytes, C) will return EMSGSIZE (except for the first send t=
o C)

Yes, at some point, there are icmp packets.

> (Last not least, because I'm too lazy to look: is that patch against
> git master or against release/2.3?)

master


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