Comment 6 for bug 1443607

Robert: okay, but it is not clear to me what is missing. Can you please test this patch and report its short-comings.

This patch relies on several things about linux bridges and devices that are not obvious:

- With Nova/libvirt/QEMU/KVM, the tap devices are created with the same MTU as the linux bridge.
- The MTU on a linux bridge is always the smallest of all the MTUs of all the devices it enslaves.
- A VLAN device automatically gets the same MTU as its parent when it is created.
- A VXLAN devices gets an MTU 50 bytes lower than its parent.

# ip -o l | cut -d' ' -f2,5 | grep eth1
eth1: 9000

# ip link add link eth1 name eth1.10 type vlan id 10
# ip -o l | cut -d' ' -f2,5 | grep eth1
eth1: 9000
eth1.10@eth1: 9000

# brctl addbr br1
# ip -o l | cut -d' ' -f2,5 | grep br1
br1: 1500

# brctl addif br1 eth1.10
# ip -o l | cut -d' ' -f2,5 | grep br1
br1: 9000

# sudo ip link add vxlan1 type vxlan id 1 group 239.0.0.1 dev eth1
# ip -o l | cut -d' ' -f2,5 | grep vxlan1
vxlan1: 8950

# brctl addif br1 vxlan1
# ip -o l | cut -d' ' -f2,5 | grep br1
br1: 8950

# brctl show
bridge name bridge id STP enabled interfaces
br1 8000.080027eb45b4 no eth1.10
       vxlan1