is there a way to have tcp act more like udp? Im currently using lua sockets and have set the tcp no_delay option, is there a way to disable or set the acknowledgement to timeout?
Related
I have an application that sends simple data over TCP (simple, no auth) and another application that must receive it. The only allowed connection between the two is UDP.
On the receiving side, I have SOCAT listening for incoming UDP packets and forwarding them via a TCP connection to the computer that hosts the software.
socat UDP4-LISTEN:5000, fork TCP-CONNECT:192.168.1.5:5001
On the sending side, I can send test data via
socat UDP4-connect 192.168.1.1:5000
There is a firewall in the way and I have no control over it which is why UDP is my only option. The firewall allows UDP out from the sender and UDP in to the receiver.
What I don't know is how to take a TCP connection on the sender and forward its output via UDP. And I don't know if this is the best way or if it will work at all.
Thank you
As socks5 rfc says,
A UDP association terminates when the TCP connection
that the UDP ASSOCIATE request arrived on terminates.
I wonder, doesn't "the TCP connection that the UDP ASSOCIATE request arrived on" just terminate when it timeouts? As there is no more data need to be sent in that TCP connection.
Should the client send meaningless data in that TCP connection just to keep it alive while it need the UDP association?
I wonder, doesn't "the TCP connection that the UDP ASSOCIATE request arrived on" just terminate when it timeouts?
No. The TCP connection is kept alive as a signal that the proxied UDP socket is still valid. Without it the client has no way of knowing whether the server is still reachable or whether the UDP socket is still allocated.
Similarly, without the TCP connection the server has no other way of knowing whether the client is still connected.
Should the client send meaningless data in that TCP connection just to keep it alive while it need the UDP association?
There's no need to send meaningless data. Just keep the connection alive. TCP has a built-in keepalive mechanism which can be turned on.
Edit: It's worth pointing out that the default TCP keepalive times on both Linux and Windows is fairly long. See this question on ways of tweaking it for specific sockets.
I developed a TCP backend using boost asio and now I need to access the whole TCP packet (header + body). It is possible using TCP sockets?
In this introduction article: http://tldp.org/HOWTO/TCP-Keepalive-HOWTO/overview.html
It states that reasons for TCP keep alive are:
Preventing disconnection due to network inactivity
Detect dead peers
So in my application, there is a busy TCP socket. Packets are frequently sent back and forth between the two peers - so there is a good amount of packets with ACK flag set.
The application protocol uses other means for dead peer detection.
Is TCP keepalive still necessary for the case above?
No. TCP keepalive is practically a 0 byte-long tcp packet. If you can be sure on your app protocol, it is unneeded.
First of all, is there any problem with using both UDP and TCP on the same server?
Secondly, can I use the same port number?
Yes, you can use the same port number for both TCP and UDP. Many protocols already do this, for example DNS works on udp/53 and tcp/53.
Technically the port pools for each protocol are completely independent, but for higher level protocols that can use either TCP or UDP it's convention that they default to the same port number.
When writing your server, bear in mind that the sequence of events for a TCP socket is much harder than for a UDP socket, since as well as the normal socket and bind calls you also have to listen and accept.
Furthermore that accept call will return a new socket and it's that socket that you'll then have to also poll for receive events. Your server should be prepared to continue accepting connections on the original socket whilst simultaneously servicing multiple clients each of which will be triggering receive events on their own sockets.
Firstly,there is no problem using both tcp and udp on the server.
Secondly,we can have both UDP and TCP requests on same port ,because each request is identified by a quintuple contained by source IP ,Destination IP, Source Port, Destination Port, PROTOCOL(as protocol can be TCP or UDP).