Contiki IPv4 UDP broadcast packets not sending

Question

I'm currently implementing my first application in Contiki on a Telos bmote and encountered a problem.

For my application (which utilises the uIP IPv4 stack) I need to be able to broadcast messages to all nodes.

I have looked through the source and found that in uip_over_mesh.c the packet is found to be for an external network and is then being sent to a gateway node on the network instead of being distributed to all nodes. If no gateway node is present it just drops the packet. So in fact rather than the packet being broadcast to all the nodes in the network it's either just being dropped or being sent to just the gateway node and external network.

My problem is that I need it to broadcast to the other nodes in the network(as it should), is there a step I'm missing or am I doing something wrong?

Thanks :)

p.s. This is the rough code to get the message to send.

struct uip_udp_conn *udp_conn = udp_broadcast_new(UIP_HTONS(5001), state);
udp_bind(udp_conn,UIP_HTONS(5001));
uip_udp_packet_send(udp_conn, "hello",5);

---

Sorry that my question didn't seem clear. To clarify what I wanted to do was send an IPv4 UDP packet to the broadcast address i.e. send to all devices on the network using the all ones addr. But I found that the sending device would only forward the message to a gateway node if it was present on the network.

Answer 1

After lots more reading of the Contiki source I found that the problem lay in uip_over_mesh.c. When a broadcast message(255.255.255.255) was being sent it was tripping up when the send function would check if the destination was within the local network (based on the netmask and destination address). Failing this it would then try to send it out to a local gateway(if one existed) to route it out of the network.

Although IPv4 UDP broadcast had been built into the api, I saw no evidence of it actually being implemented in the uip_over_mesh.c(I might be wrong and totally missed it). So to fix this I added a broadcast RIME channel and added a check for the all ones address where the previously mentioned gateway check was. A method to receive the broadcast messages was also implemented ensure broadcast message were correctly received and passed to the upper layers.

From what I gathered from here and the mailing list, IPv6 is where the focus is and not many people are knowledgeable or using the IPv4 uip stack. When I get some time I will dig up my modified uip_over_mesh.c and see if I can push the modifications, though I'm sure it's a bit of a hack and not of much use due to the above mentioned lack of interest.

Answer 2

The question is not clear but what I understand from the question you want to broadcast a message anonymously to all neighbour motes. You have two choices to go.

1. If you are using RIME stack from contiki. There is already a code under example/rime/example-broadcast.c (have a look at line 79,80 ( packetbuf_copyfrom("Hello", 6); broadcast_send(&broadcast)); I have tested the code and it is working perfectly fine under teleosB. I strongly recommend you to go with uIP (IPv6) stack using RPL. For a large network it 'll be extremely hard to maintain rime stack.

2. You can use udp based ipv6 enable broadcast example from examples/ipv6/simple-udp-rpl. You do n't need to change anything for receiver function unless you want more additional features. This function 'll print receiver port, sender port and data length. You can add "addr" from "uip_ipaddr_t" in the receiver function if you want to print IP addresses. For sender the lines of code are (76-91). You do n't need to change for simple message like "hello". I tested the code and it works perfectly fine.