On 03/11/2010 04:20 PM, Joe Conway wrote:
Interestingly after a reboot:
# brctl show bridge name bridge id STP enabled interfaces br0 8000.18a9051f09f0 no eth0
# ifconfig br0 UP BROADCAST RUNNING MULTICAST MTU:576 Metric:1 eth0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 lo UP LOOPBACK RUNNING MTU:16436 Metric:1
So what is causing br0 MTU == 576 here?
Following up, I tested on a Fedora 12 VM that was pretty much a clean install from 2 months or so ago. First I changed the network settings to match my host machine, and rebooted the VM. This is what I saw:
---------------- # ifconfig br0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 eth0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 lo UP LOOPBACK RUNNING MTU:16436 Metric:1 ----------------
Looks good so far.
Next I did a "yum update" and rebooted. Keep in mind that this is in a VM, so I am not running libvirt, qemu, kvm, etc. at all. Now I see:
---------------- # ifconfig br0 UP BROADCAST RUNNING MULTICAST MTU:576 Metric:1 eth0 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 lo UP LOOPBACK RUNNING MTU:16436 Metric:1 ----------------
Here you can see br0 MTU = 576 even though eth0 MTU is 1500. So the issue seems to be generic with some recent package update.
Unfortunately since the VM had been idle for a long while, there were hundreds of packages updated.
Anyone have any idea what package would determine the default MTU for a bridged network device?
Thanks,
Joe