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

From: Mike Lovell
Subject: Re: [Qemu-discuss] DHCP reply packet got dropped in bridged network
Date: Thu, 06 Nov 2014 17:10:29 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.1.2

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.


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