On Mon, Jun 06, 2016 at 08:50:49AM +0200, Martin Pieuchot wrote: > On 06/06/16(Mon) 13:04, Masao Uebayashi wrote: > > Broadcast frame, coming into a bridge'ed interface, passes if_input() 3 > > times, > > and actually input (ether_input()) twice. > > > > - A frame enters an interface (e.g. pair(4)), the interface calls if_input() > > on it. The frame is queued in if_input_queue. > > > > - A task running if_input_process() is triggered. It takes the frame and > > calls bridge_input(). Frame is queued in bridgeintrq. > > > > - bridge_process() dispatches frame as multicast/broadcast (if > > (ETHER_IS_MULTICAST())) and calls bridge_ifinput() on it, then passes the > > frame to bridgeintr_frame(). > > > > - bridgeintr_frame() calls bridge_broadcast() on it. > > > > - bridge_broadcast() calls bridge_localbroadcast(), which again calls > > bridge_ifinput(). > > > > bridge_ifinput() is called twice for each broadcast frames. > > bridge_ifinput() > > calls if_input(). Thus 3 if_input() for each. > > > > These duplicate frames confuse pppoe(4), that's why it stops working. > > What do you mean by "confuse pppoe(4)"? I still don't understand what's > the link between pppoe(4) and bpf(4) in this case and why BPF matters > for a kernel driver.
- PPPoE client (pppoe(4)) sends a PPPoE Discovery "initiation" frame, which is broadcast. - PPPoE server (npppd(8)) receives 3 copies of it via bpf(4), then returns 3 PPPoE Discovery "offer" frames. - pppoe(4) receives 3 "offer" frames and gets confused ... somehow. I don't know the internal of pppoe(4) yet. pppoe(4) might have a bug, it might be able to work even if it receives 3 replies at once, I don't know. I don't think that npppd(8) receiving 3 copies of broadcast frames (via bpf(4)) is an intentional design anyway.
