How to troubleshoot Internet connectivity issues

Jephe Wu -

Situation: packet loss on Internet between countries, one end ip is, other end is
Objective: use free tools to troubleshoot the issue

1. ping
ping -c 100 to check the RTT and packet loss rate

2. traceroute or tracert

check the RTT time for each hop.

You can paste the result to to get the location information.

3. tcptraceroute or traceroute -T(CentOS 5)

If the udp normal traceroute is not able to go through, you can try tcptraceroute or traceroute -T

4. telnet or nc

telnet serverip portnumber to check the connectivity

nc -vz servername portnumber to check if tcp portnumber is open,

nc -zv jephe01 22
Connection to jephe01 22 port [tcp/ssh] succeeded!

nc -zuv 123
Connection to 123 port [udp/ntp] succeeded!

5. mtr (My TraceRoute) -

use mtr to check packet loss and RTT time.

6. wireshark(GUI) or tshark(CLI)

use tshark to monitor packet loss (tcp retransmission)

7. tcpdump to check if the traffic is coming into the server

References:  - IP Locator