quetion about xen
 

What is the difference between xenbr and virbr ?It puzzled me.I would appreciate any help .

what is virbr? i can't see any reference to it anywhere apart from in japanese...

I have these packages installed on RHEL5.1 X86_64 SERVER :
$ rpm -qa|grep xen
xen-libs-3.0.3-41.el5
kernel-xen-2.6.18-53.1.4.el5
xen-3.0.3-41.el5
$ rpm -qa|grep virt
libvirt-0.2.3-9.el5
virt-manager-0.4.0-3.el5
python-virtinst-0.103.0-3.el5
libvirt-python-0.2.3-9.el5
and I issued the ifconfig command in dom0:
$ ifconfig
virbr0
Link encap:Ethernet HWaddr 00:00:00:00:00:00
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:39 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 b) TX bytes:7620 (7.4 KiB)

xenbr0
Link encap:Ethernet HWaddr FE:FF:FF:FF:FF:FF
inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
UP BROADCAST RUNNING NOARP MTU:1500 Metric:1
RX packets:7440 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:379308 (370.4 KiB) TX bytes:0 (0.0 b)
In my opinion,I consider that vif in domU are attached to virbr0 by default since them have the same subnet as virbr0 ,but actually them are attached to xenbr as described in /etc/xen/scripts/network-bridge