em(4) losing link when if_bridge(4) addm/deletem are used

[Andrew Thompson]

On Wed, Mar 28, 2007 at 03:30:45PM -0700, Jeremy Chadwick wrote:
> On Thu, Mar 29, 2007 at 09:37:09AM +1200, Andrew Thompson wrote:
> > On Tue, Mar 27, 2007 at 08:33:27PM -0700, Jeremy Chadwick wrote:
> > > In the midst of the madness, I found that when doing either of the
> > > following commands...
> > > 
> > >   ifconfig bridge0 addm em1
> > >   ifconfig bridge0 deletem em1
> > > 
> > > ...I see the entire em1 interface completely reset, bringing down link,
> > > then up again shortly after.  The logs on my switch also confirm this.
> > > 
> > The only other thing the bridge does to the interface when removing it
> > is to reinstate IFCAP_TXCSUM, which is disabled when the interface is
> > bridged. If you manually toggle this with ifconfig do you get the same
> > result?
> 
> Bingo.
> 
> medusa# ifconfig em1 -txcsum
> medusa# ifconfig em1
> em1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
>         options=8<VLAN_MTU>
>         inet 10.0.0.2 netmask 0xffffff00 broadcast 10.0.0.255
>         ether 00:30:48:71:60:6b
>         media: Ethernet autoselect
>         status: no carrier
> medusa# grep em1 /var/log/messages
> Mar 28 15:29:34 medusa kernel: em1: link state changed to DOWN
> Mar 28 15:29:36 medusa kernel: em1: link state changed to UP

As a workaround you could remove txcsum at boot, then the bridge will
not toggle it. Long term you could prod the em(4) maintainer to see if
this can be resolved.


Andrew