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I configured my Debian (with KVM on board) as following:

/etc/network/interfaces:

auto lo
iface lo inet loopback

auto  eth0
iface eth0 inet manual

auto vmbr0
iface vmbr0 inet static
  address 176.x.y.133
  netmask 255.255.255.224
  gateway 176.x.y.129
  bridge_ports eth0
  bridge_stp off
  bridge_fd 0
  dns-nameservers 8.8.8.8 8.8.4.4

After reboot I have following ifconfig (ip a):

1: lo: ...
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
    link/ether AA:BB:CC:DD:EE:FF brd ff:ff:ff:ff:ff:ff
    inet6 fe80::a60:6eff:feDD:EEFF/64 scope link 
       valid_lft forever preferred_lft forever
3: vmbr0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN 
    link/ether AA:BB:CC:DD:EE:FF brd ff:ff:ff:ff:ff:ff
    inet 176.x.y.133/27 brd 176.x.y.159 scope global vmbr0
    inet6 fe80::a60:6eff:feDD:EEFF/64 scope link 
       valid_lft forever preferred_lft forever
4: venet0: <BROADCAST,POINTOPOINT,NOARP,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN 
    link/void 
    inet6 fe80::1/128 scope link 
       valid_lft forever preferred_lft forever

So eth0 and vmbr0 having the same MAC-addresses (AA:BB:CC:DD:EE:FF). Is it bad or should it be so?

Extra: I want create a network with VMs on KVM-Host, where VMs are having public IPs (I have one main IP for the KVM-Host and two additional single IPs for the VMs).

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1 Answer

up vote 6 down vote accepted

This is as it should be. eth0 is the physical interface, vmbr0 is the bridge that KVM creates for the guests. Since it is attached to eth0, it has eth0's MAC address.

Extra: Since you're using bridged networking, simply give your first guest machine the second public IP. It should just work.

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I had also a tap100i0 interface, which was created as I created the bridge (vmbr0) and this had another MAC-addr. Is the tap100i0 kind of related to the vmbr0? I tried to give the second public IP, but it doesn't work: arp and IP tables are empty and I'm not able to add static routes to the GW (RTNETLINK: no such process and SIOCSARP: network unreachable) –  static Jul 15 '13 at 20:04
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