I am looking for a way to test UDP connection, I tried with some VPN servers that I know they have XXX UDP port open, but I didn't know what to send in the body, when I send random strings I don't get any respond
Is there any reliable server that have some UDP port open all time and respond to my connections
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I have a command line program using UDP socket and a UDP hub server running fine on my local host with seperate command prompts. Each the server and the client are bidirectional, so they both need to be able to send and recieve from each other.
I think that all i need to do to make them run on two seperate computers is to change the IP addresses and port numbers respectively. I think i will need to use the private IPV4 address because my socket is UDP IPV4. But i can't confirm because I do not have two different computers. Can someone please reassure me?
For instance, let's say I have basic UDP client and UDP server:
UDP Client is running on a computer with IPV4 162.16.156.1
UDP server is running on a computer with IPV4 162.18.200.1
UDP server should:
- bind to 162.18.200.1
- send to 162.16.156.1
- recieve would happen at 162.18.200.1
UDP client should:
- connect to 162.18.200.1
- send to 162.18.200.1
- recieve would happen at 162.16.156.1
THIS IS ALL UDP
Let say I have an internal port 25000 that isn't forwarded.
I send a UDP Message through that port to a server.
I now listen to that 25000 port locally for a reply from that server.
The server received my message.
The server thinks the port the message came from is 27833.
How much time does the server have to send a message back to me through port 27833?
If I locally keep listening to port 25000 will the 27833 port stay open indefinitely until I stop listening?
I'm not an expert but I think the timeout of the forwarding of the port on the NAT will not be influenced because you listen to new datagram on a computer behind your NAT (As only the OS will know you want to read those packets, not the NAT).
For the time the port will be forwarded by the NAT, I've find this response on stackoverflow: For how long a router keeps records in the NAT and can they be reused forwarding requests from other hosts? (Shortcut from the response, in practice less than 120 sec)
My friend told me that TCP doesn't need port forward.
What exactly he said is if the server is port forwarded the client can request something and the server will respond without port forward.
And I agreed with that even though I'm not sure it is true.
Later he said it is the same with UDP which I do not believe.
MAINLY THE QUESTION IS
If a client requests something on a server with TCP, does it need to be port forwarded to receive the response?
Also is it the same for UDP?
If the request from the client is a SYN for connect call then only a SYN-ACK response will be allowed through NAT. If the NAT supports simultaneous open connection then a SYN response from server will also be allowed through NAT. After the connection is established then client and server can communicate freely without any restriction. Port forwarding is not needed.
For UDP after a packet from client to server is sent then anything from server can be received through exact same public port of the NAT from which the first packet was sent. No port forwarding needed.
I have around 20 clients communicating together with a central server in the same LAN. The clients can make transaction simultaneously with the server. The server forward each transaction to external appliance in the network. Sometimes it works, sometimes my application shows a "time out" message in a client screen (randomly)
I mirrored all traffic and found TCP Retransmission after TCP Reset packets for the first TCP Sequence. I immediately thought about packet loss but all my cables/NIC are fine, and I do not see DUP ACK in the capture.
It seems that RST packets may have different significations.
What causes those TCP Reset?
Where should I focus my investigation: network or application design ?
I would appreciate any help. Thanks in advance.
Judging by the capture, I assume your central server is 137.56.64.31. What's happening is the clients are initiating a connection to the server with a SYN packet and the server responds with a RST. This is typical if the server has no application listening on that particular port e.g. the webserver application isn't running and a client tries to connect to port 80.
The clients are all connecting to different ports on the server, which is unusual for an central server, but not unheard of. The destination ports the clients are connecting to on the server are: 11007, 11012, 11014, 11108, and 11115. Is that normal for the application? If not, the clients should be connecting to whatever port the application server is listening on.
The reason for the retransmits is that instead of giving up on the connection upon receiving a RST from the server, the client tries to initiate the connection again so Wireshark considers it a retransmission.
I am looking at traffic generated by my computer when socks server is defined.
I read over the internet and see that its possible to route udp also trough the proxy server.
when i try using different apps that uses UDP and allows socks settings, it uses it only for tcp traffic. why?
I have defined SOCKS5, as i understand that v4 doesnt support udp (why?)
i tried an example, Vuze client - its expert mode allows to prefer udp traffic, setup socks server and even at this point, any udp goes directly to peers.
My wish is to monitor the traffic and see how its transmitted, is it over UDP connection with socks server, or does it actually connects to the socks server in TCP and sends the data, which is then sent via udp to the destination?
When a client wants to relay UDP traffic over the SOCKS5 proxy, the client makes a UDP associate request over the TCP. SOCKS5 server then returns an available UDP port to the client to send UDP packages to.
Client then starts sending the UDP packages that needs to be relayed to the new UDP port that is available on SOCKS5 server. SOCKS5 server redirects these UDP packages to the remote server and redirects the UDP packages coming from the remote server back to the client.
When client wants to terminate the connection, it sends a FIN package over the TCP. The SOCKS5 server then terminates the UDP connection created for the client and then terminates the TCP connection.
Double SSH Tunnel Manager support SOCKS5 With UDP
3proxy Server support UDP