forwarding didn't work if wlan0 is member of a bridge

Alexander V. Chernikov melifaro at
Wed Jan 13 22:10:05 UTC 2016

13.01.2016, 13:02, "Olivier Cochard-Labbé" <olivier at>:
> On Wed, Jan 13, 2016 at 9:45 AM, Alexander V. Chernikov <melifaro at>
> wrote:
>>  I suspect the reason here is link state bridge handling.
>>  ix0 does not seem to have IFCAP_LINKSTATE option but re(4) does. Probably
>>  wlan0 doesn't have LINKSTATE option.
>>  Code in bridge_linkcheck() doesn't handle the case with both "has link
>>  state" and "no link state" interfaces well:
>>  if reX is the only interface w/ IFCAP_LINKSTATE and it goes down, bridge
>>  will also change its link state to down.
>>  (However, bridge does not seem to have link state option itself, so
>>  RT_LINK_IS_UP() macro should return true...)
> ​For validating your "IFCAP_LINKSTATE" hypothesis, I've plug an USB
> ethernet adapter ue(4) that didn't support IFCAP_LINKSTATE.
> And I've setup the bridge0 with wlan0 and ue0 (in place of re1): same bug
> triggered. I need to ​plug a cable for correct routing.
We discussed/investigated this behaviour on IRC. To summarise:
1) ip_tryforward() does check interface linkstate regardless of linkstate capability
2) bridge linkcheck function does not seem to care about linkstate capability.

What happened in original case:
802.11 does not provide linkstate cap and actual linkstate value is 0 (unknown).
re0 does provide linkstate cap, so on link down, bridge_linkcheck() code decided to set own linkstate as DOWN as well (has non-zero linkstate interface, 0 up).
On packet transmission. ip_tryforward() checked bridge0 state, found it to be DOWN so the icmp_error() was triggered.

Attached patch fixes the problem, but I'm still thinking about better solution.

>root at fbsd-router:~ # ifconfig bridge0
> bridge0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu
> 1500
>         ether 02:6b:c0:de:b8:00
>         inet netmask 0xffffff00 broadcast
>         nd6 options=9<PERFORMNUD,IFDISABLED>
>         groups: bridge
>         id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
>         maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
>         root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
>         member: ue0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
>                 ifmaxaddr 0 port 7 priority 128 path cost 55
>         member: wlan0 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
>                 ifmaxaddr 0 port 5 priority 128 path cost 33333
> root at fbsd-router:~ # ifconfig ue0
> mtu 1500
>         options=80008<VLAN_MTU,LINKSTATE>
>         ether 00:19:fd:4e:77:4d
>         media: Ethernet autoselect (none)
>         status: no carrier
>> ​Regards,
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