If by "manually" you mean "instruct telnet
to send SYN and ACK packets", then no. This is done by the operating system, which needs to keep track of all TCP parameters for a connection – sequence numbers, window size, etc.
It would be possible for a program to use raw IP sockets and manage the TCP layer all by itself. But it's generally an incredibly pointless thing to do – it would copy a lot of code from kernel.
If you are trying to learn how TCP works, try Scapy. It can create and send packets using given parameters, including TCP. (You'll probably have to use a packet sniffer to watch for such things as SYN+ACK though.)
You can use with
nmap -sS
family instead of scapy, scapy has been used for writing exploit. – PersianGulf – 2016-01-19T07:59:28.037Could you explain why this is needed? – user1686 – 2011-04-07T04:47:56.320
I'm learning about TCP/IP and there is a server that has been set up that I can experiment with. – tony_sid – 2011-04-07T05:27:35.707