Another tool that makes the same use of the TCP handshake is tctrace. Much like tcptraceroute, tctrace sends a SYN packet to a specific host and if the reply is a SYN/ACK, the port is open. An RST packet indicates a closed port.

To start tctrace, enter the following command:

    # tctrace -i<device> -d<targethost> 

-i <device> is the network interface on the target and -d <target host> is the target.

For this example, we are going to run tctrace against the www.example.com domain:

    # tctrace -i eth0 -d www.example.com
  

The following output is obtained:

     1(1)   [172.16.43.1]
     2(1)   [172.16.44.1]
     3(all)  Timeout
     4(3)   [172.16.46.1]
     5(1)   [172.16.47.1]
     6(1)   [172.16.48.1]
     7(1)   []
    ...
    14(1)   [172.16.56.1]
    15(1)   [172.16.57.1]
    16(1)   [198.148.81.137] (reached; open)