I need to write an application in Node.js which sends some UDP packets to a given IP address and Port as well as listening for UDP packets from the same IP and Port.
Other examples i have seen all seem to mention a Client and Server architecture with one side sending and the other receiving. I need to do both in one app.
My question is: Can i send and receive on the same socket or should i have one for each as below?
const Send= dgram.createSocket('udp4');
const Recieve= dgram.createSocket('udp4');
Thanks
You only need one socket - it's possible to both send and receive on the same one.
However to be able to receive the socket will need to be "bound" to a local port using socket.bind().
Related
I want to be able to receive SYN packets from a client, but not send back a SYNACK response. I have tried a few things. If you use raw sockets, it is possible to receive the full packet but linux kernel seems to automatically send back a FINACK packet. I found out that this was because I did not have a service actually listening to the port I was monitoring. My next step was to bind a socket to the port I was interested in, and use the listen() syscall to listen to that port, along with the raw socket. This approach results in the kernel automatically sending back a SYNACK rather than a FINACK. Is there anyway to receive a raw packet, and not send back an automated response? It seems that raw sockets can only snoop on packets, rather than actually handle them. I have also tried using a UDP server socket to listen to the target port, but I am still sending back an automatic FINACK.
I am trying to send and receive an TCP packet with data on it. My current line of code for sending is:
send(IP(src="1.1.1.1",dst="1.2.3.4")/TCP()/"Test")
How would I specify a Port
I have an simple idea:
port = random.randint(48620, 49150)
If you want to know what is port, go to:
https://www.techtarget.com/searchnetworking/definition/port-number
Thanks
Introduction
I am currently trying to build up a networking layer for Unity from scratch. Currently I am testing the communication via UDP using Node.js for the server and the client. However I guess the language of the implementation will not matter for what I am asking for.
Current approach
The current approach using Node.js for the server and the client is pretty basic. I simply send a packet from a client to my server while the client and the server are not in the same local network. Both are behind a router and therefore also behind a NAT.
The server then sends back an answer to the IP and port received within the UDP packet that was sent from the client.
Problem
I am curious about the security on the client side regarding to ports being opened on the client machines and routers. So far I assumed that I don't need to do anything to secure the client from attackers or anything else that can do something with the ports that are used by my application. The following assumption shows why I think that I don't need to do anything to secure the clients.
Assumption
Server is setting up callbacks.
Server starts listening to a specific port which is also forwarded to the servers machine within the router.
Server now will call a callback when a UDP message was received. The server then will send a UDP message to the address and the port of the client obtained by the message received.
Client is setting up callbacks.
Client starts listening to port 0 which for Node.js's dgram means:
For UDP sockets, causes the dgram.Socket to listen for datagram messages on a named port and optional address. If port is not specified or is 0, the operating system will attempt to bind to a random port. - https://nodejs.org/api/dgram.html#dgram_socket_bind_port_address_callback
So the operating system now knows that packets sent to this port belong to my application.
Nobody can use this for something malicious.
Client, which knows the servers address and port, starts the process of sending a UDP message to the server.
Clients router receives the UDP message. NAT creates a random port (used on the public side) and maps it to the clients (local) address and port.
So the router now knows that packets sent to the public address and the newly generated port belong to the local address and port.
Nobody can use this for something malicious.
Clients router sends UDP message containing the public address and the NAT generated port to the server.
The worst thing that can happen is that a man-in-the-middle attacker can read the data the client is sending. Due to it is only gamedata like positions and so on that is sent this is not a big problem while developing the basics.
Nobody can use this for something malicious.
Server receives the message and calls the callback described in 3. So the server sends to the public address and the NAT generated port of the client.
The worst thing that can happen is that a man-in-the-middle attacker can read the data the server is sending. Due to it is only gamedata like positions and so on that is sent this is not a big problem while developing the basics.
Nobody can use this for something malicious.
Same as 7. with the servers router and the servers local address and port.
Same as 8. with the servers router.
Client receives the UDP message of the server and calls a callback which processes the message contents.
Due to the local port of the client is bound to my application only nobody can use this for something malicious due to I simply ignore the contents if they are not from the real server.
Question
So is my assumption correct and I really don't need to secure the client from any attacks that will harm the clients in any way?
I'm writting a program that simulates nodes in network. Every node is listening to some port on local for incoming requests. If a request is received it replies to sender of the request. The reply is sent after a socket is created associated with the address of the sender of the request. Since sender is using some port on localhost and has used bind to listen to id, trying to bind to the same port with an other process results in a messages that states that the port is already taken (bound).
How should I solve this in order to be able to simulate server/client on the same machine? I am using UDP protocol for this program.
You solve this by using different ports for client and server interaction. A useful example would be how client and server interact during DHCP. The client sends requests via UDP on port 67 and the server sends responses back via UDP on port 68.
The question is the title.
But I'd like to describe my problem so that someone can suggest an alternative solution.
I know that when the client sends a message on a socket to 12.34.56.78:40, the router on the client's side sets a rule for some time that any data received from the 12.34.56.78:40 is allowed and will be sent to the client machine on the network.
so the problem I have is that the client is sending to the server on some port but the server needs to reply using a different socket (thus a different port). but ofcourse the server's ip didnt change.
so that was my first idea of solving the problem
spoof the outgoing port
Multiple sockets can bind to the same port, and thus send packets with the same source port number, if the each socket sets the SO_REUSEPORT socket option. See the SO_REUSEPORT socket option and the difference between SO_REUSEADDR and SO_REUSEPORT.