Re: [PATCH 0/9][RFC] KVM virtio_net performance

[Bill Davidsen <davidsen@tmr.com>]

Avi Kivity wrote:
> Bill Davidsen wrote:
>>
>> I have been discussing this (on this list) in another thread. Putting 
>> tcpdump on the eth0 device in the VM, the br0 device in the host, and 
>> the eth0 (physical NIC) in the host, you can see that when the VM 
>> generates a DHCP request it shows up on the br0 in the host, but 
>> never gets sent on the wire by eth0.
>>
>> That's the point of failure, at least using RHEL5/FC6/kvm-66 as the 
>> environment.
>
> Does playing with the bridge forward delay ('brctl setfd') help?
>
Update: Redhat has a user chain in iptables shared between INPUT and 
FORWARD (bad idea) which doesn't pass bootp packets by default. Adding 
the following rules to that table solved the DHCP for me.

ACCEPT     udp  --  anywhere             anywhere            udp 
spt:bootps dpt:bootpc
ACCEPT     udp  --  anywhere             anywhere            udp 
spt:bootpc dpt:bootps

This seems to solve my problem, I just have to make it part of my "start 
kvm" procedure.

-- 
Bill Davidsen <davidsen@tmr.com>
  "Woe unto the statesman who makes war without a reason that will still
  be valid when the war is over..." Otto von Bismark