Today I want to show you a real good network administration tool, if you do network administration, you should use ping and traceroute to check whenever a host is alive or not.
Maybe the steps of testing is first ping the server, and if there is no response, you try with traceroute to see where in the route an interruption exists.
Traceroute works sending ICMP packets to all the routers in the way to the destination host, but these days more and more routers and server have the ICMP packets filtered, so here is where tcptraceroute comes to save the day.
As you may guess from its name tcptraceroute is like traceroute but sends tcp packets instead of ICMP packets thus avoiding the filtering of the packets in the route.
Debian / Ubuntu
apt-get install tcptraceroute
Fedora / Centos
Be sure to have Dag Wieers repository enabled and then run:
yum install tcptraceroute
tcptraceroute [-nNFSAE] [ -i interface ] [ -f first ttl ] [ -l length ] [ -q number of queries ] [ -t tos ] [ -m max ttl ] [ -p source port ] [ -s source address ] [ -w wait time ] host [ destination port ] [ length ]
This is going to send packets to tcp port 80 and will show you the route to reach www.yahoo.com host, here is part of the output at my home.
10 tbr1.attga.ip.att.net (18.104.22.168) 220.728 ms 222.896 ms 220.617 ms 11 cr1.attga.ip.att.net (22.214.171.124) 220.735 ms 219.452 ms 219.639 ms 12 cr2.wswdc.ip.att.net (126.96.36.199) 227.361 ms 225.108 ms 225.065 ms 13 tbr2.wswdc.ip.att.net (188.8.131.52) 226.671 ms 224.096 ms 226.067 ms 14 184.108.40.206 217.532 ms 217.472 ms 218.654 ms 15 220.127.116.11 204.243 ms 212.031 ms 204.132 ms 16 ge-3-1-0-p170.msr2.re1.yahoo.com (18.104.22.168) 216.304 ms 215.201 ms 215.220 ms 17 gi1-23.bas-a2.re3.yahoo.com (22.214.171.124) 202.054 ms 203.112 ms 201.714 ms 18 f1.www.vip.re3.yahoo.com (126.96.36.199) [open] 202.302 ms 201.899 ms 209.557 ms
tcptraceroute mail.entelnet.bo 25
This is going to send packets to tcp port 25 to my ISP mail server, and here is the output.
Tracing the path to mail.entelnet.bo (188.8.131.52) on TCP port 25 (smtp), 30 hops max 1 * * * 2 172.17.158.5 13.467 ms 13.143 ms 13.204 ms 3 184.108.40.206 13.285 ms 13.170 ms 13.259 ms 4 220.127.116.11 30.819 ms 34.117 ms 33.918 ms 5 s1011.entelnet.bo (18.104.22.168) [open] 32.282 ms [unknown, ACK] 33.101 ms 40.572 ms
You may want to read tcptraceroute man page