When STP is enabled on a bridge interface used on a libvirt network, DHCP requests fail 75% of the time during PXE boot. If I drop to the iPXE prompt, and send a few more dhcp requests, I'll often get a reply by the 3rd or 4th attempt. I've verified via dnsmasq logging + tcpdump that the requests are never actually making it to the server. Disabling STP on the corresponding bridge fixes.
Serge Hallyn seems to think its due to upstream commit @ https://bugzilla.redhat.com/show_bug.cgi?format=multiple&id=605953
libvirt-bin 0.9.8-2ubuntu7
qemu-kvm 1.0+noroms-0ubuntu4
kvm-pxe 5.4.5
<network>
<name>cobbler-devnet</name>
<uuid>7976ddf2-4e92-e15a-7b4d-2948542a3349</uuid>
<forward mode='nat'/>
<bridge name='virbr1' stp='on' delay='0' />
<mac address='52:54:00:C2:5D:94'/>
<ip address='192.168.123.1' netmask='255.255.255.0'>
<dhcp>
<range start='192.168.123.2' end='192.168.123.254' />
<host mac='00:16:3e:3e:aa:02' name='node02' ip='192.168.123.102' />
<host mac='00:16:3e:3e:aa:03' name='node03' ip='192.168.123.103' />
<host mac='00:16:3e:3e:aa:01' name='node01' ip='192.168.123.101' />
<host mac='00:16:3e:3e:a9:1a' name='cobbler' ip='192.168.123.2' />
<bootp file='pxelinux.0' server='192.168.123.2' />
</dhcp>
</ip>
</network>
Marking confirmed as I've seen other mention of this.
Your bridge is virbr1. What does virbr0 look like? Can you show your full network in context (/etc/network/