ipsend can be compiled in two ways. The first is used to send one-off packets to a destination host, using command line options to specify various attributes present in the headers. The destination must be given as the last command line option, except for when TCP flags are specified as a combination of A, S, F, U, P and R, last.
The other way it may be compiled, with DOSOCKET defined, is to allow an attempt at making a TCP connection using a with ipsend resending the SYN packet as per the command line options.