Hey, make sure you disable tso and gso in your guest

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so yeah, srn found a bug;    the NIC offloading stuff has always not worked properly for virtual guests... but with the latest RHEL/CentOS kernel it's gone from 'you drop a few packets every now and then'  to "takes down your guest entirely if you send just one packet"  

So yeah, uh,  we'll change the starting image to add

ethtool -K eth0 tso off gso off 

to /etc/rc.local.   Please do the same on your guest.

details from srn:

4 separate domu's have been seeing an instance of this bug - probably more will do so as they upgrade:

http://xen.crc.id.au/bugs/view.php?id=3

This behavior on the dom0 side (disconnecting when it sees a packet that is too large) was introduced in 2.6.18-348.4.1.el5.  It is not present in .6.18-348.3.1.el5.  It is still present in 2.6.18-348.6.1.el5 (latest.)

40 of our servers have 2.6.18-348.4.1.el5.

There is a bug fix:

http://lists.xen.org/archives/html/xen-devel/2013-04/msg01328.html

But I don't know what the status of that is WRT centos.  I guess this redhat bug is related:
https://bugzilla.redhat.com/show_bug.cgi?id=957231

But without a redhat account we can't look.

domu's can work around this (apparently with some performance impact) by running

ethtool -K eth0 tso off gso off

Considering we have 40 servers running 4.1 and only 4 people have been affected, is the best thing to do just to send a list out to announce / the blog and throw swatch on the console logs?

I may poke at the centos virt mailing list and ask if they know if there's a timeline for applying the patch to netback I linked to above.

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This page contains a single entry by luke published on May 23, 2013 3:03 PM.

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