>From James's duplicate bug:
In our MAAS based openstack deployment, we provide MTU via DHCP to all
servers to enable jumbo frames.
This works fine until juju creates the bridge devices for LXC or KVM
containers, at which point we reliably lose the MTU 9000 setting on the
bridge, resulting in all sorts of MTU related fun in things like
corosync and percona-cluster which are running under lxc.
We've fixed this by appending an explicit mtu set to the bridge
definition in /etc/network/interfaces:
auto juju-br0
iface juju-br0 inet dhcp
bridge_ports eth0
post-up /sbin/ip link set eth0 mtu 9000
After making this change, we can reliably reboot physical hosts
container lxc containers, an not break our clusters.
The issue is that MTU has to be set on the underlying device, not the
bridge itself - this may actually be something we can fix in the
dhcpclient tools
** Changed in: juju-core
Status: Invalid => Triaged
** Changed in: juju-core
Importance: Undecided => Medium
** Tags added: kvm lxc network
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https://bugs.launchpad.net/bugs/1403955
Title:
DHCP's "Option interface-mtu 9000" is being ignored on bridge
interface br0
Status in juju-core:
Triaged
Status in isc-dhcp package in Ubuntu:
Confirmed
Bug description:
In an env with jumbo frames enabled, and using MAAS as DHCP server,
the client receives the following IPv4 lease:
$ cat /var/lib/dhcp/dhclient.br0.leases
lease {
interface "br0";
fixed-address 10.230.20.26;
filename "pxelinux.0";
option subnet-mask 255.255.248.0;
option dhcp-lease-time 43200;
option routers 10.230.16.1;
option dhcp-message-type 5;
option dhcp-server-identifier 10.230.20.1;
option domain-name-servers 10.230.20.1;
option interface-mtu 9000;
option broadcast-address 10.230.23.255;
option domain-name "ctsstack.qa.1ss";
renew 3 2014/12/17 16:48:15;
rebind 3 2014/12/17 21:52:09;
expire 3 2014/12/17 23:22:09;
}
The interfaces show the following config after boot:
$ ifconfig br0
br0 Link encap:Ethernet HWaddr a0:d3:c1:01:9d:58
inet addr:10.230.20.26 Bcast:10.230.23.255 Mask:255.255.248.0
inet6 addr: fe80::a2d3:c1ff:fe01:9d58/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:530530 errors:0 dropped:0 overruns:0 frame:0
TX packets:1591569 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:68713489 (68.7 MB) TX bytes:213710979 (213.7 MB)
$ ifconfig eth0
eth0 Link encap:Ethernet HWaddr a0:d3:c1:01:9d:58
inet6 addr: fe80::a2d3:c1ff:fe01:9d58/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:10539274 errors:0 dropped:3394 overruns:0 frame:454
TX packets:2627412 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2320560616 (2.3 GB) TX bytes:3562885157 (3.5 GB)
Interrupt:32
"option interface-mtu 9000;" from the lease file is being ignored by br0.
Could it be related to eth0 MTU size? If that's the case, shouldn't both
interfaces be updated?
Other info:
$ brctl show br0
bridge name bridge id STP enabled interfaces
br0 8000.a0d3c1019d58 no eth0
$ cat /etc/network/eth0.config
iface eth0 inet manual
auto br0
iface br0 inet dhcp
bridge_ports eth0
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