Hetzner, kvm and connection lost

[Stoned]

Hi everyone !
Sorry for my very bad english
I tried to install kvm for virtualization on a Hetzner EQ4 server and i would like to use the 3 addtional ip for 3 virtual machine..but i have a little problem: the virtual machine seem to working fine, it take the assigned ip address..but after some minutes it lost connection! The virtual machine continue to work, but without connection: i try to connect them using vnc through ssh tunnel on the host machine, and i can login, but there isn't external connection.
The machine is unreachable also from host machine.
So, after some minutes, the network restart to working always for some minutes, then i lost the connection again.
The connection with host server workin always fine.
This is my configuration:
Host : Debian minimal (with only package kvm libvirt-bin virtinst bridge-utils fail2ban vim-nox)
Guest : Debian Lenny installed with virt-install
I modified only /etc/sysctl.conf that actualy is

net.ipv4.conf.all.rp_filter=1
net.ipv4.icmp_echo_ignore_broadcasts=1

net.ipv4.ip_forward=1
net.ipv6.conf.all.forwarding=1
net.ipv4.conf.default.proxy_arp=1

and /etc/network/interfaces that actualy is

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
#allow-hotplug eth0
#iface eth0 inet dhcp
auto eth0
iface eth0 inet manual

auto br0
iface br0 inet static
	address   xxx.xxx.xxx.106
	broadcast xx.xxx.xxx.127
 	netmask   255.255.255.224
 	gateway   xx.xxx.xxx.97
        bridge_ports eth0
        bridge_fd 9
        bridge_hello 2
        bridge_maxage 12
        bridge_stp off

All other file are untoched
On virtual machine i assigned the new ip (xx.xxx.xxx.117) and the host address as gateway (xxx.xxx.xxx.106)
my ifconfig return

br0      Link encap:Ethernet  HWaddr bb:bb:bb:bb:bb:bb  
          inet addr:xxx.xxx.xxx.106  Bcast:xxx.xxx.xxx.127  Mask:255.255.255.224
          inet6 addr: yyyy::yyyy:yyyy:yyyy:yyyy/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1670 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1369 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:143571 (140.2 KiB)  TX bytes:189891 (185.4 KiB)

eth0      Link encap:Ethernet  HWaddr aa:aa:aa:aa:aa:aa  
          inet6 addr: yyyy::yyyy:yyyy:yyyy:yyyy/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1615 errors:0 dropped:0 overruns:0 frame:0
          TX packets:997 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:146089 (142.6 KiB)  TX bytes:149866 (146.3 KiB)
          Interrupt:250 Base address:0x8000 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:0 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:0 (0.0 B)  TX bytes:0 (0.0 B)

vnet0     Link encap:Ethernet  HWaddr bb:bb:bb:bb:bb:bb  
          inet6 addr: zzzz::zzzz:zzzz:zzzz:zzzz/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:374 errors:0 dropped:0 overruns:0 frame:0
          TX packets:651 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:500 
          RX bytes:47999 (46.8 KiB)  TX bytes:61678 (60.2 KiB)

It's normal that br0 and vnet0 had the same mac address ? On my local server, br0 always had eth0 mac address...

Someone can help me ?

[Stoned]

I don't know if it's the cause or the consequence, but when i lost connection i can see on the /var/log/messages of host system

Feb  9 16:52:31 server1 kernel: [  897.631377] eth0: received packet with  own address as source address