touch-packages team mailing list archive

[Victor Tapia <victor.tapia@xxxxxxxxxxxxx>]

Hi Robie,

Let me answer your questions:

> Why is br0 being set up to bridge eth0? Is something doing this automatically or is this configuration necessary for something (if so, what?)?
This configuration (br0 on a single physical interface) is automatically generated by deploying openstack Juno (I don't know what particular component does it, atm) on Trusty. In our case it's not necessary/mandatory, but just the result of the installation. I don't know what consequences we might face by disabling/removing br0, though.

> Without using br0 and just using plain eth0, does the interface-mtu option work correctly?
Will do asap, but on a first guess I think it would work

>... If so, I'm not sure it really makes sense for the DHCP client to set the MTU on eth0 when receiving DHCP over br0. I suppose it depends on the use case though.
I agree. In this particular scenario, having just one physical interface sharing its mac address with the bridge, I think it makes sense to expect the interface's MTU being set (there's no other interface acting as a constraint). Other situations, with several interfaces, manual config might be mandatory.

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Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu.
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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