Symptom: You have just booted the Xen-kernel and no traffic escapes dom0. This is because the firewall discards the packages.

Solution: Enable the xenbr0 forwarding:

1. Open the file /etc/sysconfig/SuSEfirewall2 in your favorite editor.
2. In step 33 change FW_FORWARD_ALWAYS_INOUT_DEV="" to FW_FORWARD_ALWAYS_INOUT_DEV="xenbr0".
3. Restart the firewall: /etc/init.d/SuSEfirewall2_setup restart

You should now be able to ping other hosts.