tcpdump on DomU's eth1

Hi,

I have a machine with 2 physical network interfaces: eth0 and eth1.
I'm using FC6Xen on both Dom0 and DomU. I want to do network sniffing on 
DomU's eth1.
When I do a tcpdump on DomU's eth1, I see nothing. But when I do it on 
Dom0's eth1, I can see the traffic. I have enabled promiscuous mode on 
Dom0's and DomU's eth1. What could possible went wrong?
When I do a "ifconfig", I see peth0 but not peth1. Why is this so?

The list of bridges are shown below:
# brctl show
bridge name     bridge id               STP enabled     interfaces
xenbr0          8000.feffffffffff       no              vif2.0
                                                        peth0
                                                        vif0.0
xenbr1          8000.feffffffffff       no              vif2.1

Hope someone can help.

Chee Sin