netcat은 네트워크상 접속에서 raw 데이타를 읽고 쓸수있는 프로그램입니다.

GNU netcat 0.7.1, a rewrite of the famous networking tool.
Basic usages:
connect to somewhere:  nc [options] hostname port [port] ...
listen for inbound:    nc -l -p port [options] [hostname] [port] ...
tunnel to somewhere:   nc -L hostname:port -p port [options]

Mandatory arguments to long options are mandatory for short options too.
Options:
  -c, --close                close connection on EOF from stdin
  -e, --exec=PROGRAM         program to exec after connect
  -g, --gateway=LIST         source-routing hop point[s], up to 8
  -G, --pointer=NUM          source-routing pointer: 4, 8, 12, ...
  -h, --help                 display this help and exit
  -i, --interval=SECS        delay interval for lines sent, ports scanned
  -l, --listen               listen mode, for inbound connects
  -L, --tunnel=ADDRESS:PORT  forward local port to remote address
  -n, --dont-resolve         numeric-only IP addresses, no DNS
  -o, --output=FILE          output hexdump traffic to FILE (implies -x)
  -p, --local-port=NUM       local port number
  -r, --randomize            randomize local and remote ports
  -s, --source=ADDRESS       local source address (ip or hostname)
  -t, --tcp                  TCP mode (default)
  -T, --telnet               answer using TELNET negotiation
  -u, --udp                  UDP mode
  -v, --verbose              verbose (use twice to be more verbose)
  -V, --version              output version information and exit
  -x, --hexdump              hexdump incoming and outgoing traffic
  -w, --wait=SECS            timeout for connects and final net reads (시간설정)
  -z, --zero                 zero-I/O mode (used for scanning)
                              (최소한의 데이타 이외에는 보내지 않도록 하는옵션) 

Remote port number can also be specified as range.  Example: '1-1024'