[Xen-users] NAT on dom0 = network checksum errors in pv domU

[Richie <listmail@xxxxxxxxxxxx>]

I ran into an issue today which I (somewhat) understand can occur when 
NAT is involved on dom0 and the network interface is paravirtualized on 
the guest.   When my pv domU was requesting a dhcp lease it would fail 
to ever accept the offer and instead show a checksum error for each 
packet. I am setting up a new xen installation where iptables has a 
basic setup for regulating incoming external interface traffic as well 
masquerading anything coming in from the lan to the internal interface 
(which is now bridged for xen).
A similar issue is documented here:
http://wiki.xensource.com/xenwiki/XenFaq#head-4ce9767df34fe1c9cf4f85f7e07cb10110eae9b7
However, disabling tx checksum offload from within the domU *did not* help

I had to address it as described here:
https://bugzilla.redhat.com/show_bug.cgi?id=474191
by disabling it against the virtual interface in dom0 which doesn't 
exist until after the pvm has started.
I did not try the patch here -> 
http://lists.xensource.com/archives/html/xen-devel/2006-03/msg01445.html 
which does seem related.
I created a quick hack, which is working good enough for now [ given the 
amount of time I spent troubleshooting this as well as the fact that I'm 
by no means a network guy :) ]

So, for those of you that have/had encountered this issue, what are you 
doing to address it properly?


--- vif-bridge.orig     2010-05-15 16:45:28.000000000 -0400
+++ vif-bridge  2010-05-15 16:46:06.000000000 -0400
@@ -83,6 +83,7 @@
     online)
        setup_bridge_port "$vif"
        add_to_bridge "$bridge" "$vif"
+        /usr/sbin/ethtool -K "$vif" tx off
         ;;
 
     offline)

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