I have strange problem with multicast server/client application. I wrote simple server and client udp multicast application in C and I tested it using two laptops and one wireless router.Server is connected with the ethernet cable to the wrt54gl linksys router with 192.168.1.101 IP address. Client with IP 192.168.1.105 address is connected to the router via wireless interface. They can ping each other. Server is sending UDP packets using sendto function and client is receiving them using recvfrom function. When I run my server I can see sent udp packet in wireshark destined for multicast group with IP address 226.1.1.1 but on client side I don't receive those packets and also I can't see them in wireshark. I'm pretty sure that code is properly written. Do you have experience with multicast to advice me?
Thank you
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I need to communicate Arduino module with my Phone through ESP8266 wifi module
They all link to the local LAN network and didn't know the IP address of each other, so I plan to send UDP broadcast message from my phone, but ESP8266 module seems doesn't receive the message
The ESP8266 library I use is from here:
https://github.com/itead/ITEADLIB_Arduino_WeeESP8266
and use the function registerUDP() and recv()
Can somebody help me?
I don't have enough reputation to leave a comment so I will make an answer.
I have a feeling that your registerUDP() need to specify an IP address and I guess you are supplying your DHCP assigned IP address. Where as the UDP broadcast is sent using a multicast or broadcast IP.
You can modify the initiator code to send UDP packet to all IP within the same subnet (e.g. 192.168.1.1 to 192.168.1.254) and see if it works.
Please if you can help me about my problem. On one side I have server with IP 172.27.13.2 connected to the WAN interface of router 172.27.13.1 ...Then on wireless LAN of my router 192.168.1.1 I have connected a few clients. Now I will write code in C where client are requesting some UDP streams from server, then server broadcasts streams to clients, and if some packets get lost clients must send NACK to server. My questions is:
Because server and clients are on different subnets how can I broadcast from server?
And how the client can send request and NACKs to server because they are in different subnets?
Are these problems can be solved by router configurations or in C code?
Thank you for helping
You cannot broadcast to different subnets. Routers do not usually forward broadcast packets to different subnets, unless you have a very special router that can be configured properly (e.g. Cisco ...). You could however use multicast for such a task. Here's a C example
Also check this: UDP broadcast packets across subnets
NOTE: some includes in the c example are missing, but they are easy to find
As both server & users are in different subnets .As router donot forward broadcast .But we have solution by modifying the router configuration .
If you have cisco router & users are connected on cisco switch ,you can use ip helper address command on switch on vlan .You can allow udp packet on router ACL
Am just beginner of this socket programming ...
i tried to make a UDP client_server program using SOCK_RAW .I can send message from the server part.But in client part am getting garbage values. And the receiving message packet size also different.Can U help me to do this client server program using SOCK_RAW.
I tried this client -server with eth0 & eht1,i tried to send 1 packet from eth0 to eth1 sending side is showing "OK" message.. but received data is garbage..
before i done normal client server program using UDP protocol.I got correct output from normal udp client server .When i tried with SOCK_ROW its showing error in sending part.
Make your life simpler and use SOCK_DGRAM - Kernel will take care of datagram headers, you only need to provide valid IP address and data. It is user's responsibility to append (before transmitting) and parse (upon reception) UDP headers using SOCK_RAW.
Most likely you are seeing IP and UDP headers and calling them "garbage". That is what SOCK_ROW does. You should parse and skip protocol headers if you want to get to your message content while using SOCK_ROW.
I am writing a content filter in C using the socket API that will intercept DNS requests, and only return the response if the domain is allowed. The pseudocode to describe this is:
Redirect all DNS queries to the content filter program which is listening on UDP port X.
Content filter program extracts domain being queried and determines if it is allowed or not.
If it is allowed, then the content filter program forwards the original DNS request packet to the original destination DNS server while maintaining the original source and IP+port so that the DNS server can send the reply directly back to the client.
If the domain is not allowed, then no reply is sent.
I currently have the program listening on UDP port X but the problem is that I can't access the IP headers, and therefore can't simply forward the DNS request to the original server while maintaining the original headers.
I have tried using socket(AF_INET, SOCK_RAW, IPPROTO_UDP) but that doesn't bind on port X (understandably), and doesn't receive any traffic.
What is the best way to go about listening on UDP port X, while still being able to access the IP headers of incoming packets?
I think recvfrom on an UDP socket should give you the correct source address. You still probably need a raw socket for forwarding the message.
The functionality for SOCK_RAW based sockets varies depending on the platform you are on. Generally, when you want to get access to the full IP datagram information, then I would recommend using the Berkeley Packet Filter to tap the data-link layer frames addressed to UDP port of interest.
I'm new to this forum (at least at asking questions), so please be patient. I'm trying to write simple client-server applications to communicate using datagram (UDP) sockets, with C and Windows.
The scenario is very simple, I want to be able to send/receive data from a machine in some local network (behind a GATEWAY/NAT) to some host having public IP. I can send the data, but it seems impossible to receive any data back, because the remote server can't see the client's local IP.
I don't want the user to perform manual port forwarding on the GATEWAY, and I also don't want to use UPnP because of security issues (though it also should be enabled by the user).
I think it is possible because applications like Skype or Browsers can do it, but how ?
Are there some automatically forwarded ports or things like that ? I'm exhausted of searching the web ... PLEASE HELP !
For UDP connections, most home NAT gateways will automatically create a temporary reverse mapping for each outbound packet.
Consider a scenario where your client is running on the internal machine with IP address 192.168.4.5, sending a UDP packet from port 65000 to the external address 64.34.119.12:6789, via a gateway with external IP address 192.0.43.10. When the gateway sees your internal client send a UDP packet from 192.168.4.5:65000 to the external address, it will NAT it to an external address and port, like 192.0.43.10:5500. Your server will see a packet with a source address of 192.0.43.10:5500 and destination address 64.34.119.12:6789. The router also sets up a reverse mapping, so that if it sees a packet arrive on the external interface with a source of 64.34.119.12:6789 and a destination of 192.0.43.10:5500, it will redirect it back to 192.168.4.5:65000. This mapping typically times out after a short while.
This means that in simple cases, all you need to do is:
On the client, use the same port to send to the server and listen for responses;
On the server, respond to the client at the address and port that the client's packet was receieved from, using the same server port that recieved the packet;
Have the client send the initial packet in the conversation;
Don't leave the "connection" idle for more than a few minutes at a time.