this is obsolete doc -- see http://doc.nethence.com/ instead

XEN network configuration 

Dom0 

Clean up the config file, 

cd /etc/xen/

mv xend-config.sxp xend-config.sxp.dist

sed '/^#/d; /^$/d' xend-config.sxp.dist > xend-config.sxp

and choose some kind of xen network configuration: 

http://pbraun.nethence.com/doc/sysutils_xen/network_bridge.html 

http://pbraun.nethence.com/doc/sysutils_xen/network_hybrid.html 

http://pbraun.nethence.com/doc/sysutils_xen/network_nat.html 

http://pbraun.nethence.com/doc/sysutils_xen/network_route.html 

DomU mac addresses 

XEN mac addresses start with '00:16:3e'. You can either let XEN generate random mac addresses for each guest or force them within its configuration, 

vif = [ 'vifname=vifname,mac=xx.xx.xx.xx.xx.xx' ]

It may be necessary on a bridged network configuration (depending on your local network area policies). Otherwise I recommend not to define any mac address in guest's configuration nor inside guest's system (remove ifcfg-eth0:HWADDR on redhat systems). It's just easyer and spares you some time. 

TCP offloading 

You might experience some troubles with networking in some guests. You'll have to disable TCP offloading within it. Disabling it on the dom0 side (on guest's vif) doesn't seem to help. But if you really want to, here you go, 

for type in rx tx sg tso ufo gso gro lro; do

  ethtool -K vguest.0 $type off 2>&1 | grep -v 'Operation not supported'

done

for tap vifs (HVM guests) also add, 

for type in rx tx sg tso ufo gso gro lro; do

  ethtool -K tap-vguest.0 $type off 2>&1 | grep -v 'Operation not supported'

done

References 

http://wiki.xensource.com/xenwiki/XenFaq 

http://www.gentoo.org/doc/en/xen-guide.xml 

http://www.excentral.org/archives/2007/03/23/rhel5-xen-nating