Ethernet bridging weirdness

[Scott Phelps]

On Sep 14, 2010, at 4:39 PM, Douglas Stanley wrote:

> On Tue, Sep 14, 2010 at 3:57 PM, Serge E. Hallyn
> <serge.hallyn at canonical.com> wrote:
>> Quoting Douglas Stanley (douglas.m.stanley at gmail.com):
>>> Hello all,
>>>
>>> I'm about at my wit's end, and I really hope some one might be  
>>> able to
>>> shed some light on this topic for me.
>>>
>>> I have two physically identical servers, both running 10.04.1, both
>>> are completely up to date. Both are set up to be kvm hosts. On both
>>> machines, I have an IDENTICAL /etc/network/interfaces, the only
>>> difference being two lines where ip addresses are specified.
>>>
>>> The problem is, that both machines need a bridge set up on boot, so
>>> that virtual machines can access it. One machine works 100% fine,  
>>> the
>>> other, the second bridge never comes up!
>>>
>>> My /etc/network/interfaces file can be seen at:
>>> http://gist.github.com/579592
>>>
>>> Also, I just did a fresh re-install of 10.04.1, and performed the
>>> updates on the machine that isn't working, thinking that maybe I did
>>> something slightly different during the initial install. But it  
>>> still
>>> doesn't work.
>>>
>>> If I type:
>>> sudo ifup br1
>>> I get: "ifup: interface br1 already configured". But, ifconfig  
>>> doesn't
>>> list either my eth2 or my br1 devices. Also, brctl show doesn't list
>>> my second bridge. But, if I edit /var/run/network/ifstate and remove
>>> the br1=br1 line, then run "sudo ifup br1", it comes up just fine.
>>> Similarly, if I "sudo ifdown br1;sudo ifup br1" that also works.
>>
>> Well br1 is manual, without a specified address.  As opposed to br0
>> which is static with an address.  So I wouldn't expect it to show up
>> with ifconfig.  Does it not show up with 'ifconfig -a' or 'brctl  
>> show'?
>> Can you not specify an address for it (either using ifconfig or with
>> dhclient)?
>>
>
> True, it is manual, but it's a bridge. I can't seem to find it now,
> but that's precisely how it was supposed to be configured, according
> to the documentation I was going by (I think it was one of the KVM
> oriented guides). And, no, it's not showing up when I do a brctl show
> on this one server (it shows up fine on the other *identical* server).
>
>>> Any idea why it isn't coming up automatically on boot, when my other
>>
>> Because 'manual' means 'unconfigured', different from 'static' which
>> means manually pre-configured.
>>
>
> But the other server with identical hardware, and identical config,
> and identical interfaces file (except for 2 lines where ip addresses
> are specified), works differently. On that box, the bridge shows up
> fine using brctl show.



Try removing 'bridge_maxwait 0' from the config.  The bridge setup  
scripts will not wait for the bridge ports to enter a forwarding state  
if set to 0 and may be failing as a result.

//Scott