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

Bill Davidsen
2008-07-27T13:15:36Z

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