Linux Ethernet Bridging - Feb 2011 - [Bridge] Bridge suddenly only passes traffic if in promiscuous mode

Hello,

I have a bridge to various interfaces. There is an IP address on the 
bridge, and hosts on the interfaces connected to the bridge use the 
bridge's IP address as a gateway. STP is off and the forwarding delay is 
set to 0.

This has been working fine, however, today I needed to change around 
some IPv6 addresses on the connected hosts. I made the IPv6 changes and 
rebooted those boxes, only to find that suddenly no traffic -- IPv4 *or* 
IPv6 -- was passing through the bridge.

When I pulled up tshark to see what was going on, traffic suddenly 
started flowing again. And even as I type this, as long as tshark is 
running on that interface (no matter what the capture filter is), 
traffic is flowing. The moment I stop tshark from running, traffic 
stops. IOW, the bridge is only passing traffic while in promiscuous mode.

I didn't change the IP address on the bridge itself. As far as I can 
tell I didn't do anything odd whatsoever. But I have no idea what's 
causing this and I'd really like to not reboot the box if at all possible.

Does anyone have any idea what might be causing this and/or how to 
troubleshoot this?

Thanks,
Jeff

On 02/08/2011 11:29 AM, Jeff Mitchell wrote:
> Hello,
>
> I have a bridge to various interfaces. There is an IP address on the
> bridge, and hosts on the interfaces connected to the bridge use the
> bridge's IP address as a gateway. STP is off and the forwarding delay
is
> set to 0.
>
> This has been working fine, however, today I needed to change around
> some IPv6 addresses on the connected hosts. I made the IPv6 changes and
> rebooted those boxes, only to find that suddenly no traffic -- IPv4 *or*
> IPv6 -- was passing through the bridge.
>
> When I pulled up tshark to see what was going on, traffic suddenly
> started flowing again. And even as I type this, as long as tshark is
> running on that interface (no matter what the capture filter is),
> traffic is flowing. The moment I stop tshark from running, traffic
> stops. IOW, the bridge is only passing traffic while in promiscuous mode.
>
> I didn't change the IP address on the bridge itself. As far as I can
> tell I didn't do anything odd whatsoever. But I have no idea what's
> causing this and I'd really like to not reboot the box if at all
possible.
>
> Does anyone have any idea what might be causing this and/or how to
> troubleshoot this?
What kernel version?

And, you are sniffing the physical interface, or the bridge?

Maybe send us output of brctl show, and ifconfig -a?

Promisc bit is sometimes hard to detect properly, so if you can, please
post /sys/class/net/[iface-name]/flags
If bit 0x100 is set, the NIC is actually promisc, regardless of what
ifconfig -a shows.

Thanks,
Ben
>
> Thanks,
> Jeff
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> Bridge mailing list
> Bridge at lists.linux-foundation.org
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-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com