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Document mcast+ipv6 (Was: Re: socket, mcast looping back frames -> IPv6 broken)

Message ID 20130401001251.GD17794@type.youpi.perso.aquilenet.fr
State New
Headers show

Commit Message

Samuel Thibault April 1, 2013, 12:12 a.m. UTC 
Stefan Hajnoczi, le Mon 11 Mar 2013 09:36:14 +0100, a écrit :
> > Otherwise we may just document that one has to disable Duplicate Address
> > Detection to get IPv6 working :/
> 
> Seems like this might be the only way for now.

Here is a patch

Samuel


Document how to get IPv6 working with mcast socket

Document that IPv6 can not work in mcast mode unless disabling DAD in
the guest.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

Comments

Stefan Hajnoczi April 8, 2013, 11:13 a.m. UTC | #1 
On Mon, Apr 01, 2013 at 02:12:51AM +0200, Samuel Thibault wrote:
> Stefan Hajnoczi, le Mon 11 Mar 2013 09:36:14 +0100, a écrit :
> > > Otherwise we may just document that one has to disable Duplicate Address
> > > Detection to get IPv6 working :/
> > 
> > Seems like this might be the only way for now.
> 
> Here is a patch

Let's check out the 2 socket patch first.  If that doesn't work out I'll
merge the documentation warning.

Stefan
Samuel Thibault April 8, 2013, 12:11 p.m. UTC | #2 
Stefan Hajnoczi, le Mon 08 Apr 2013 13:13:19 +0200, a écrit :
> On Mon, Apr 01, 2013 at 02:12:51AM +0200, Samuel Thibault wrote:
> > Stefan Hajnoczi, le Mon 11 Mar 2013 09:36:14 +0100, a écrit :
> > > > Otherwise we may just document that one has to disable Duplicate Address
> > > > Detection to get IPv6 working :/
> > > 
> > > Seems like this might be the only way for now.
> > 
> > Here is a patch
> 
> Let's check out the 2 socket patch first.  If that doesn't work out I'll
> merge the documentation warning.

Sure.

Samuel
diff mbox

Patch

diff --git a/qemu-options.hx b/qemu-options.hx
index c40ba55..9074a24 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1683,6 +1683,12 @@  mcast support is compatible with User Mode Linux (argument @option{eth@var{N}=mc
 @url{http://user-mode-linux.sf.net}.
 @item
 Use @option{fd=h} to specify an already opened UDP multicast socket.
+@item
+Since with multicast diffusion the guest will receive its own frames, its IPv6
+Duplicate Address Detection (DAD) will erroneously detect a duplicate, thus
+preventing IPv6 from working.  One has to disable DAD to get IPv6 working, for
+instance on Linux by setting the sysctl @code{net.ipv6.conf.all.accept_dad} to
+0.
 @end enumerate
 
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