Re: [Xen-users] Help creating virtual networks of domU guests

[Ernst Bachmann <e.bachmann@xxxxxxxx>]

On Monday 18 July 2005 15:08, Carl Holtje ;021;vcsg6; wrote:
> This is incorrect.. bridging is happy with eth0 and eth0:1 interfaces..

Well, no. While it may accept eth0:1, it still enslaves the HW interface:

# brctl show
bridge name     bridge id               STP enabled     interfaces
pan0            8000.0010a70aab7a       no              eth0

# ifconfig eth0:test 192.168.100.1 up

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:10:A7:0A:AB:7A
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:300487012 errors:0 dropped:0 overruns:0 frame:0
          TX packets:249994141 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:2540897286 (2423.1 Mb)  TX bytes:3489368961 (3327.7 Mb)
          Interrupt:11

eth0:test Link encap:Ethernet  HWaddr 00:10:A7:0A:AB:7A
          inet addr:192.168.100.1  Bcast:192.168.100.255  Mask:255.255.255.0
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  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:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:11

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:898243 errors:0 dropped:0 overruns:0 frame:0
          TX packets:898243 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:249587829 (238.0 Mb)  TX bytes:249587829 (238.0 Mb)

pan0      Link encap:Ethernet  HWaddr 00:10:A7:0A:AB:7A
          inet addr:192.168.1.21  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:300486998 errors:0 dropped:0 overruns:0 frame:0
          TX packets:249994141 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:2629045622 (2507.2 Mb)  TX bytes:3366380547 (3210.4 Mb)

# brctl addbr test
# brctl addif test eth0:test
device eth0:test is already a member of a bridge; can't enslave it to bridge 
test.

Bang. eth0 is already bridged, so the alias ifaces can't be bridged any more.

> my understanding is that it creating the eth0:1 inteface does just that --
> creates a (virtual) device just the same as a real device, and loads a new
> TCP stack.. for all intensive purposes, it's a stand-alone device..

Also, from the linux kernel documentation:
/usr/src/linux/Documentation/networking/alias.txt

-- 
IP-aliases are additional IP-addresses/masks hooked up to a base
interface by adding a colon and a string when running ifconfig.
This string is usually numeric, but this is not a must.
--
They're IP only, thats far from being a real ethernet network iface.

Hope that brought some light in the issue,
/Ernst

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