Hello,
my eventual goal is to implement MRP and for that I started to program a
bit and stumbled over a problem I don't understand.
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?
If someone wants to reproduce this locally, I can simplify my program
and provide it here. I tested this on a Debian 4.15 kernel (x86), but
also with the same symptoms on an arm64 with 4.16 and a dsa switch.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |
