Xen and network issues.

Warren Togami wtogami at redhat.com
Tue May 8 19:21:47 UTC 2007


Mike McGrath wrote:
> We've got issues.  Many of our xen guests are experiencing tcp checksum 
> corruption.  Research on the net suggests ethtool -K eth0 tx off will 
> fix the issue but it hasn't in our case.  I've tried the koji guest on 
> many physical hosts, same issue.  It's been on two FC6 dom0 hosts and a 
> RHEL5 dom0 host.
> For now I'm going to stick koji on app1 as a physical host.  Just 
> because that box has gotten to the point where it becomes unusable and 
> we cannot have that happening right now.
> 
> I've contacted some internal xen developers, some guys in ##xen on 
> freenode and the Fedora-xen list.  Anyone who is able I'd encourage you 
> to take a look as well.  Simple test:
> 
> "tcpdump -vvv | grep incomplete"
> 
> You'll see:
> 06:34:20.135530 IP (tos 0x0, ttl  64, id 39370, offset 0, flags [DF], 
> proto: TCP (6), length: 40) nat-pool.fedora.phx.redhat.com.49457 > 
> publictest8.fedora.phx.redhat.com.http: P, cksum 0x76af (incorrect (-> 
> 0x6100), 601:601(0) ack 6801 win 597
> 

If worse comes to worse I know a workaround for this that eliminates the 
problem, but also adds a bit more inconvenience.  It involves creating a 
private NAT network on each Xen host, with the extra real IP on the 
hosts real ethernet device, and NAT.

Warren




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