My client app is sending http req to routers webserver. The server responds with the intended data but the wireshark traffic shows that after every transaction, The server is sending [RST,ACK] & [RST] tcp packets which i believe is not a good idea.
My client creates (and close) new socket for every http transaction. But from [RST] it seems like my client is sending packet on the server's closed socket. In my recv function, the server response is "An existing connection was forcibly closed by the remote host"
do{
ret_err = recv(MySocket, recv_buffer, RECV_BUFF_LENGTH, 0);
if (ret_err == SOCKET_ERROR){
break; /* Ignoring errors [server response : "An existing connection was forcibly closed by the remote host" */
}
} while(ret_err != 0);
HANDLE_WINSOC_ERR(shutdown(MySocket, SD_RECEIVE));
closesocket(MySocket);
Packet 9 (see below image) is http reply msg from the server which contains FIN flag; which could mean that i should respond with [FIN,ACK] not just [ACK] as seen in the below diagram [my client app responded with only ACK i.e. at Packet 10].
As i am working on application layer, is their a mechanism to transmit FIN signal after recv ?
My client app is using Winsoc.
Related
I understand that the client and the server are connected after client receives SYN ACK messages from the server during 3 way handshake and sending ACK messages to the Server. After they are connected, when the client sends the other messages to the server, what happens if that messages arrives at the server before the ACK message that client sent when doing the 3 way handshake?
what happens if that messages arrives at the server before the ACK message that client sent when doing the 3 way handshake?
ACK is just the flag in the TCP header together with the sequence number of the latest received data. It can be contained in an empty packet (i.e. no payload, just TCP header) but also in a packet with payload. It does not matter if a specific packet with an ACK is received as long as an ACK covering the data is received at all.
This means it is sufficient if the initial data send by the client cover the final ACK for the TCP handshake. In fact there is not even a need to send a standalone ACK (without payload) from the client at all to finish the TCP handshake but the client can start sending data as soon as the client has received the SYN and ACK from the server.
Im trying to write a server client program, where client sends request through UDP socket to a server, then server responds back to a client through TCP socket.
My question is, how can server establish a TCP connection back to a client after getting the request through UDP?
I'll add code parts on Monday, but I more interested in pseudocode for that. Does that mean that the client should listen on tcp port after sending udp request? So confused
when a TCP client wants to establish a tcp connection with a tcp server
it needs to send SYN and then ACK
while tcp server only sends SYN/ACK
so they are different
but , after the 3_way handshaking,
is this connection symmetric, namely, are TCP client and server in equal status
for example, after the 3-way handshake, usually the client send packet first,
can TCP server send packet first?
No, the procedure is not different at all, but instead of sending a SYN then an ACK in two different packets, the servers concatenate them by sending them via a single packet!
In the other hand, remember always that the client/server nomenclature is relative. The server is the party that remains in listening mode, while the client is the party that initiates the connection ...
After the establishment of the connection, both parties are equivalent (same status as you said: ESTABLISHED). For that reason, both can send the FIN statement to close the connection ...
After the connection is established, both ends are indeed "symmetric". Who sends first is decided by the underlying protocol and differes amongst them.
For example, HTTP starts with the GET <path> HTTP/1.0 command, while other protocols let the server give a greeting line first, and only then the client sends its request.
So in general, both ends are free to send their stuff first.
TCP Stream in a tcp dump off a remote network segment showed proper handshake and conversation up to the 8s mark followed by a 20s delay where no packets were sent from either client or server. Server send sent FIN,ACK followed shortly by client's ACK and then RST packets. Why wouldn't the client send a FIN? And is FIN,ACK the proper response for a session timeout from the server's side?
The RST means that the client had already closed the connection.
The FIN means that the server closed the connection. It's one reasonable response to a timeout.
I have TCP client application and trying to connect with Server located at remote machine.
I am able to connect it.
when I Send Message Called Hello packet the Server should respond with data and time info.
but to my surprise recv returns 0 at client.
since I can't Debug code at Server.
I am not sure but may be there is problem in encoding the message format hello packet at th client upon receiving the wrong packet server is clsoing the connection
I wanted to confirm the meaning of following sequence is
I got following info from wire shark
src IP------>dst ip SYN
dst ip ----->src ip SYN,ACK
src IP------>dst ip ACK
src IP------>dst ip continuation or non http traffic "Hello Packet"
dst ip------>ACK
dst ip------>FIN, ACK
Does this means Server is closing the connection once it receives the hello packet?
Yeah, the FIN,ACK sequence is sent by one of the entity connected when they want to close the connection