So the reason is that LVS cann't transmit skbs of greater than MTU
that have been aggregated by GRO.
And Simon Horman gived a patch to make LVS deaggregate skbs that's greater
than MTU by GSO.
Great! Thank you very much! :)
On Sat, Dec 15, 2012 at 12:38 AM, Jesper Dangaard Brouer
> On Wed, 2012-12-12 at 10:05 +0100, Florian Crouzat wrote:
> > Le 11/12/2012 22:00, Thomas Bätzler a écrit :
> > >
> > > I don't have any answers, but I can confirm the problem (and the
> > > workaround) on a box running Debian "Squeeze" with 2.6.32 directing
> > > traffic from a VIP bound to lo via NAT to an active/backup bonding
> > > interface on the backend. With "gro on" for the bonded interfaces to
> > > backend real servers, throughput was ~64K/s. With "gro off" it was
> > > ~50MB/s. It's not a general networking problem since a direct
> > > to the real server via a DNAT port forward was not impacted.
> > >
> > >>From what I gleaned from a cursory look with tcpdump it seems that the
> > > problem is caused by incorrectly calculated tcp checksums.
> > >
> > > Anybody interested in pursuing this further?
> As Julian notes, this have already been fixed in upstream kernels.
> And I have recently (Aug 2012) also fixed this for IPv6.
> > Yes, I can relate.
> > I had the same conclusions, incorrectly calculated TCP checksums leading
> > to packet drops by the next firewall (in my architecture).
> > Also fixed by disabling gro.
> Its not related to incorrect checksums, but (as you noticed) the GRO
> (Generic Receive Offload) feature. (Adjusted via ethtool -K ethX)
> > CentOS 6.2, ipvsadm-1.25-9.el6.x86_64, kernel 2.6.32-220.23.1.el6.x86_64
> FYI: I have already backported support (for GRO) for the upcoming
> RHEL6.4 and RHEL5.9 kernels. (Its also in zstream for 5.8 in
> To be exact, this fixed in kernel releases (and beyond):
> RHEL6 kernel-2.6.32-328.el6
> RHEL5 kernel-2.6.18-340.el5
> If someone needs this before its officially part of a RHEL release, I
> think I'm allowed to give you the kernel with this fix as a test kernel.
> Just let me now directly.
> Best regards,
> Jesper Dangaard Brouer
> MSc.CS, Sr. Network Kernel Developer at Red Hat
> Author of http://www.iptv-analyzer.org
> LinkedIn: http://www.linkedin.com/in/brouer
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