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Re: About bridges

Staffan Thomén <> wrote:
>I was toying with bridging three of the four ethernet ports on an
>pcengines apu4d4 recently and bumped into something that made me unsure
>if I understood how to use bridges correctly.
>My setup is like this:
>wm1 configured with an address
>wm2 no address, just up
>wm3 same as 2
>and the bridge:
>brconfig bridge0 add wm1 stp wm1 add wm2 stp wm2 add wm3 stp wm3
>This all works, packets flow and addresses are learned on all
>interfaces, but ONLY if there is a cable with a link on wm1. It seems to
>be that if there is no link on wm1 the interface (status: no carrier and
>address shows <DETACHED>) gets disabled in the bridge, which kind of
>sucks because then the host has no address and communication stops.


>So how is this supposed to work? Can I force the interface with an
>address to stay enabled somehow or is there a pseudo-device that I
>haven't found that I should be using?

My reading is that this is caused by revision 1.175 of if_bridge.c which
explicitly changed bridge(4) to behave in this way.

I have been caught out by this change in a different way. I just use
dhcpcd(8) to configure IPv6 and have static IPv4 addresses on everything
on my LAN.

When I add the upstream interface to a bridge this toggles the status
on the interface and something in dhcpcd(8) or resolvconf(8) overwrites
my /etc/resolve.conf with an empty one.

I think we should revert this change, any other opinions ?

Robert Swindells

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