[ovs-discuss] Can't obtain IP address for KVM

Flavio Leitner fbl at redhat.com
Sat Mar 29 23:43:14 UTC 2014

On Sat, Mar 29, 2014 at 03:50:42PM -0700, Jeff W wrote:
> My DHCP server is running outside too. The traffic should goes through br0, otherwise how can dhcp server get the request? 

No, you see br0 as being a port which all bridge traffic pass through
which is not true for OVS bridges.

> # tcpdump -e -i tap0 tcpdump: WARNING: tap0: no IPv4 address assigned
> tcpdump: verbose output suppressed, use -v or -vv for full protocol
> decode...  18:06:12.142002 52:54:00:93:06:08 (oui Unknown) >
> Broadcast, ethertype IPv4 (0x0800), length 342: 
> > BOOTP/DHCP, Request from 52:54:00:93:06:08 
> (oui Unknown), length 300...

That is good. Your guest is fine as you said before.

> And I can't see eth0 with command ifconfig, which is different to an
> other test I did days before on Ubuntu. The config on Ubuntu looks
> like the following: auto eth0 iface eth0 inet manual up ifconfig
> $IFACE up down ifconfig $IFACE down
> It didn't get IP too, but at least system known the eth0 was
> presenting, but for CentOS it kept saying eth0 doesn't present at all.
> I'm not sure which one is reasonable.

I've seen in the past an interface present in ovsdb, so the command
'ovs-vsctl show' listed it, but it wasn't present on the system.

The interface should appear on 'ifconfig' regardless. I suggest to
use 'ip link' instead which supports new stuff. ;-)

Anyways, likely the interface is renamed to something else and it's
not part of the bridge. That would explain why DHCP is failing. 
Either 'ifconfig' or 'ip link' will tell you the interface name.
Then it's just a matter of add the correct interface to the bridge.

> An other thing weird is when I tried virt-manager, with the network
> config advanced option "Host device br0 (not bridged)", which is
> unselectable, I'm wondering if br0 doesn't work at all? missing any
> module?

I am not sure how this works, but CentOS 6.5 might too old and
virt-manager simply lacks OVS support. You should be fine by editing the
guest xml though, assuming that the libvirt supports OVS.


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