xen discuss - Feb 2008 - The instructions you need to set up bridging on a Fedora installation

http://www.mail-archive.com/fedora-xen@redhat.com/msg01543.html

The instructions you need to set up bridging on a Fedora installation are at:-

http://watzmann.net/blog/index.php/2007/04/27/networking_with_kvm_and_libvirt

Basically what you wind up doing is disabling Xen bridging
altogether and using your linux distribution''s networking scripts to
set the bridge up reliably for your guests. The only reason not to use
Xen''s native bridging is that it tries to be distro-agnostic and the
result is predictably poor. Once you disable that (by the "/bin/true"
change above) and set up the bridge as described, you should have no
difficulty. 

Follow the link:-
http://watzmann.net/blog/index.php/2007/04/27/networking_with_kvm_and_libvirt
2. Xen-like bridging
Assuming you have one physical NIC on your host, and you want to bridge all the
guests onto the physical network, you need to setup a bridge for that and
enslave the physical NIC to it. We''ll call the bridge eth0 and the
physical device peth0. Note that the bridge device eth0 is the one that receives
an IP address. With that, you need to put two files into
/etc/sysconfig/network-scripts:
the file ifcfg-peth0 should be
DEVICE=peth0
ONBOOT=yes
BRIDGE=eth0
HWADDR=XX:XX:XX:XX:XX:XX
and the file ifcfg-eth0 should be
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
TYPE=Bridge
You also want to add an iptables rule that allows forwarding of packets on the
bridged physical NIC (otherwise DHCP from your guests won''t work):
 # service iptables start
 # iptables -I FORWARD -m physdev --physdev-is-bridged -j ACCEPT
 # service iptables save
 
 
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No luck. However, i succeeded with straightforward install SNV81 DomU at F7 Dom0
(64 bit)
attaching SNV DomU with DHCP option to libvirtd''s network.
I''ve used standard installation profile and noticed that
vif=['' ''] caused DHCP request to time out , vif =
[''bridge = virbr0'']  allowed DHCP request completed OK.
Command "brtcl show" outputs were dependent on vif entry. In first
case vif0.1 was attached to tmpbridge, in second case vif0.1 was attached to
virbr0 and brought successfully through DomU installation procedure.
 
 
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