[Bridge] Lost TCP packet

Stephen Hemminger shemminger at osdl.org
Tue Feb 14 15:46:13 PST 2006

On Tue, 14 Feb 2006 09:42:32 +0100
Louis Croisez <louis.croisez at gmail.com> wrote:

> Hi,
> i am testing two bridges by sending to it random packets using hping2.
> First i create a random-length file, then i send it a lot of time on
> the wire using this command:
> for ($i=0; $i<50000; $i++) {  hping2 -q -c 1 -d $data_len -E
> random.file  }
> My problem is that some packets are lost.
> Here is my setup:
>                PC1 ( ===== BR1 --------- BR2 ===== PC2 (
> After analysis, i determined that these packets were lost because one
> of the two bridges was in BR_STATE_DISABLED state when the lost packet
> arrived.
> In fact, the packet is thrown by the bridge because, in
> br_input.c::br_handle_frame(), state==BR_STATE_DISABLED which force
> the code to jump to the err: tag at the end of this function.
> The state is set to this value while an event is received inside
> br_notify.c::br_device_event(), which do a br_stp_disable_port().
> After putting some printk in br_notify.c, i remarked that this event
> come regularly, and always related to the same bridge port (eth1).
> It don't hurt me that this event come regularly, but problem is when a
> packet is flowing in the same time thru the bridge, which cause it to
> be lost.
> I suspect a wrong bridge configuration from me. What i would like to know is:
> -  what do i wrong to get this events fired?
> -  what should i do to correct this behavior?

The hardware on eth1 is bad (cable?). The driver is telling the bridge that
the link (carrier) is going up and down. When the link is down, the bridge goes
into disabled state and drops packets. This is the correct response.

The problem is the link should not go up and down unless you pull out the cable
or something like that. What kind of hardware is on both ends of the link?

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