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[Robie Basak <1403955@xxxxxxxxxxxxxxxxxx>]

Presumably this is related to the DHCP client via dhclient and dhclient-
script, so presumably should be a task on isc-dhcp?

I see code in dhclient-script that sets the MTU based on the DHCP
option, but it doesn't have any special behaviour for br0. So I'm
wondering if this code is being used at all, or if some other
interaction is causing it to fail in this case.

Why is br0 being set up to bridge eth0? Is something doing this
automatically or is this configuration necessary for something (if so,
what?)?

Without using br0 and just using plain eth0, does the interface-mtu
option work correctly?

** Package changed: dhcp3 (Ubuntu) => isc-dhcp (Ubuntu)

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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 isc-dhcp package in Ubuntu:
  New

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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