Re: [Qemu-discuss] DHCP reply packet got dropped in bridged network

[Mike Lovell]

On 11/06/2014 04:38 PM, Xingbo Wu wrote:
> It's been bothering me for days. Currently the setup is like this:
>
> two physical machines: (1) VM host (2) dhcp server running dnsmasq. 
> Both are running archlinux with linux-3.17.2
> The host machine has two ethernet ports. a bonding interface is first 
> set up and a bridge is built on the bonding interface. br0 ( bond0 
> (eth0 eth1)).
> The bridge is configured to use dhcp and the host networking works well.
>
> But when I attach VMs to this bridge, weird things began to happen. 
> The guest uses kvm and virtio nic driver.
> part of the parameters:
>  -net bridge,br=br0 -net nic,model=virtio,macaddr=52:54:00:00:01:01

can you try a different nic model, like e1000? or can you try running 
the following iptables command?

iptables -A POSTROUTING -t mangle -p udp --dport bootpc -j CHECKSUM 
--checksum-fill

i have seen some cases where a udp checksum ends up being bad or missing 
causing dhcp to fail but not other traffic. i don't know all the details 
and your tcpdump does say the checksums are correct. its worth a try though.

mike