> On Friday 02 September 2005 17:58, Patrick O''Rourke wrote:
> > The network device on our hardware uses a rather large MTU (~16k), but
I
> > noticed that when setting up bridging, the MTU for the bridge and veth
> > device is set to 1500. Trying to set the MTU on the bridge, or eth
> > device to match that of the peth is unsuccessful:
> >
> > [root@por-hv-proto3-p4 ~]# ip link set eth0 mtu 16896
> > SIOCSIFMTU: Invalid argument
> > [root@por-hv-proto3-p4 ~]# ip link set xen-br0 mtu 16896
> > SIOCSIFMTU: Invalid argument
> >
> > We''re using xen-unstable, but a very similar issue was
discussed
> > regarding 2.0.6 on the list a while back, see:
> >
> >
http://lists.xensource.com/archives/html/xen-users/2005-07/msg00187.html
> >
> > IIRC, the poster was suggesting that the 1500 MTU limit is in the
bridge
> > or the vif code and I was wondering if this is the case.
> >
> Afaik the vif code of 2.0.x uses a 4k max ringbuffer for transfering
packets,
> and does not handle overflows of that buffer, meaning that a MTU of >4k
will
> truncate or drop all larger packets anyways.
>
> But the bridge code seems to limit the mtu to 1500, even with no real
> interfaces attached:
>
> # brctl addbr test
> # ip link set test mtu 1600
> SIOCSIFMTU: Invalid argument
>
> So, with bridging you''re stuck at 1500, with routing it might be
possible to
> raise the MTU, but that will most likely reduce overall network
performance,
> as the number of truncated packets with invalid checksum will raise...
>
> See one of the recent threads about network hangs, ping packet loss, ssh
> session hanging etc for details...
>
>
> /Ernst
Has someone found a way to do this yet? My Xen network interfaces are
not bridged, and I can neither set the MTU in domU nor in dom0
to>1500.
I''ve tried to patch the kernel, but I can''t find the piece of
code
that prevents me from setting MTU values >1500. Can anyone please
point me in the right direction?
--
Christoph Dwertmann
cdwertmann at gmx dot de
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