[virt-tools-list] problems with dhcp on bridged network

[Phil Meyer]

On 10/31/2011 05:02 AM, Cam Mac wrote:
> To reply to myself, the problem seems to be a delay (possibly due to a 
> bug?) whereby it times out. I cannot see any DHCP requests leaving the 
> br0 device. However, when I use 'crtl+b' to get into the gPXE prompt, 
> and run 'dhcp net0' some DHCP packets are sent and get a reply, and 
> the interface gets an IP address.
>
> Not sure what is going on here!
>
>
> -Cam
>
> -
>>
>>
>>
>>
>>
>>  KVM host has been set up with bridged networking, and I can 
>> successfully kickstart a host using the command line
>>
>> virt-install --name=vtest --ram 512 -f /dev/vg00/vtest --vcpus=2 
>> --network bridge=br0 -l 
>> http://10.62.128.11/mirrors/scientific/6.1/x86_64/os -x 
>> "ks=http://10.62.128.11/kickstart/vm-test.cfg console=ttyS0"
>>
>> However, I cannot get it to work when using virt-manager GUI
>>
>> I select 'Network Boot' (PXE), under 'Advanced Options', I select 
>> 'Host device em1 (Bridge 'br0'), leaving the default Mac address 
>> options, however, it fails to get a DHCP address, giving the 
>> following error in the console:
>>
>> ---------------------------8<------------------------
>>
>> Waiting for link up on net0....ok
>> DHCP (net052:54:00:35:8c:c2)......................connection timed 
>> out (0x4c106035)
>>
>> No more network devices
>>
>> ---------------------------8<------------------------
>>
>> It generates the following network config in the xml:
>>
>>
>> ----------------8<----------------
>>
>> <interface type='bridge'>
>> <source bridge='br0'/>
>> <mac address='52:54:00:35:8c:c2'/>
>> <model type='virtio'/>
>> </interface>
>>
>> ----------------8<----------------
>>
>> >From KVM guests I have kickstarted via the command line method, I can 
>> get DHCP addresses.
>> I cannot even see any DHCP requests on br0 on the KVM when it is 
>> attempting to get an address via GUI method

You need to add:

DELAY=0

to your interface definition for the bridge you are using for the VMs.

By default, the bridge will set a delay on any new MAC address to 
prevent a Spanning Tree issue.

In the case of VMs on a bridge, there should not ever be a spanning tree 
issue, so just turn the delay off.

Here is the one we use for our VMs:

DEVICE=br0
ONBOOT=yes
TYPE=Bridge
BOOTPROTO=none
DELAY=0


Good luck!