Re: [Xen-users] Re: communication between dom0 and domu

[Ernst Bachmann <e.bachmann@xxxxxxxx>]

On Saturday 03 September 2005 02:20, Marcus Brown wrote:
> Hi Arijit,
>
> Perhaps instead of a tun/tap device, try attaching a dummy to the
> bridge in dom0. You can even use multiple dummies if required with
> #modprobe -o dummy1
>
> Marcus.
>
Why would you want a dummy device attached to the bridge in dom0?

The bridge itself works as network device, so only attaching the domU's vifs 
should be enough:

# brctl addbr test

# ifconfig test 192.168.77.77

# brctl show
bridge name     bridge id               STP enabled     interfaces
test            8000.000000000000       no

## the "test" bridge has no interfaces attached.

# ifconfig test
test      Link encap:Ethernet  HWaddr 00:00:00:00:00:00
          inet addr:192.168.77.77  Bcast:192.168.77.255  Mask:255.255.255.0
          UP BROADCAST RUNNING 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:0
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

## but it has an IP Address just fine.

# ping 192.168.77.77
PING 192.168.77.77 (192.168.77.77) 56(84) bytes of data.
64 bytes from 192.168.77.77: icmp_seq=1 ttl=64 time=0.079 ms
64 bytes from 192.168.77.77: icmp_seq=2 ttl=64 time=0.039 ms

--- 192.168.77.77 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.039/0.059/0.079/0.020 ms

## which works like a charm

So, where would you need a tun/tap or dummy device?

Usually, also the real eth devices bound to bridges in dom0 shouldn't be 
configured with IP addresses, and the hosts ip-addr should be set on the 
bridge device only. The xen network scripts don't remove the IP on eth0 when 
they create a bridge, tho, so thats what might've confused you.

Hope that cleared things a bit,
/Ernst

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