Hello Willem,
On Sun, May 06, 2018 at 06:58:34PM +0200, Willem de Bruijn wrote:
> On Sat, May 5, 2018 at 10:57 AM, Uwe Kleine-König
> <u.kleine-koe...@pengutronix.de> wrote:
> > For testing purposes I created a veth device pair (veth0 veth1), open a
> > socket for each of the devices and send packets around between them. In
> > tcpdump a typical package looks as follows:
> >
> > 10:36:34.755208 ae:a9:da:50:48:db (oui Unknown) > 01:15:e4:00:00:01 (oui
> > Unknown), ethertype Unknown (0x88e3), length 58:
> > 0x0000: 0001 0212 8000 aea9 da50 48db 0000 0000 .........PH.....
> > 0x0010: 0000 0589 40f2 6574 6800 0000 0000 0000 ....@.eth.......
> > 0x0020: 0000 0100 0a80 3d38 4c5e 0000 ......=8L^..
> >
> > The socket to receive these packages is opened using:
> >
> > #define ETH_P_MRP 0x88e3
> >
> > struct sockaddr_ll sa_ll = {
> > .sll_family = AF_PACKET,
> > .sll_protocol = htons(ETH_P_MRP),
> > .sll_ifindex = if_nametoindex("veth0")
> > };
> >
> > fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_MRP));
> > bind(fd, (struct sockaddr *)&sa_ll, sizeof(sa_ll));
> >
> > So far everything works fine and I can receive the packets I send.
> >
> > If now I add veth0 to a bridge (e.g.
> >
> > ip link add br0 type bridge
> > ip link set dev veth0 master br0
> >
> > ) and continue to send on veth1 and receive on veth0 I don't receive
> > the packets any more. The other direction (veth0 sending, veth1
> > receiving) still works fine.
> >
> > Each of the following changes allow to
> > receive again:
> >
> > a) take veth0 out of the bridge
> > b) bind(2) the receiving socket to br0 instead of veth0
> > c) use .sll_protocol = htons(ETH_P_ALL) for bind(2)
> >
> > In the end only c) could be sensible (because I need to know the port
> > the packet entered the stack and that might well be bridged), but I
> > wonder why .sll_protocol = htons(ETH_P_MRP) seems to do the right thing
> > for an unbridged device but not for a bridged one.
> >
> > Is this a bug or a feature I don't understand?
>
> Packets are redirected to the bridge device in __netif_receive_skb_core
> at the rx_handler hook.
OK, thanks for finding that place. It would have taken quite some of my
time to find it.
> This happens after packets are passed to packet types attached to
> list ptype_all, which includes packet sockets with protocol ETH_P_ALL.
> But before packets are passed to protocol specific packet types (and
> sockets) attached to ptype_base[].
Still I wonder if there is something to fix in the kernel or if this
inconsistency is intended (or at least accepted).
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
