Finding out a bad or simply overloaded network link with Linux/UNIX oses

Traditionally the traceroute (print the route packets take to network host) and ping (send ICMP ECHO_REQUEST to network hosts) programs are used in a single network as diagnostic tool.

It takes some time to use both tools to diagnose such problem. However, you can use mtr program which is a network diagnostic tool. It is the combination of traceroute and ping programs (in terms of functionality) and works as a single network diagnostic tool.

How mtr works?

Once mtr invoked it starts investigates the network connection between the hosts mtr runs on and HOSTNAME by sending packets with purposely low TTLs (time to live). It will continue to send packets with low TTL, noting the response time of the intervening routers. This allows mtr to print the response percentage and response times of the internet route to HOSTNAME

During this run if you notice a sudden increase in packet-loss or response time is an indication of overloaded link or a bad link.

Examples

mtr works on both GUI and curses based terminal interface (good for remote Linux boxes).

To start mtr just type command (default is GUI interface):$ mtr upstream.router.isp.com $ mtr sl-gw9-nyc-8-0.sprintlink.net $ mtr -n router-ip $ mtr gsrmum.vsnl.net.in

Force mtr to use the curses based terminal interface:$ mtr -t www.cyberciti.biz
An example of failed router (core-router.centramedia.net):$ mtr core-router.centramedia.net

Use mtr from shell/perl script:$ mtr -c 5 -r gsrmum.vsnl.net.in >/tmp/output.vsnl.routerWhere,

-c: Use this option to set the number of pings sent to determine both the machines on the network and the reliability of those machines.
-r: This option puts mtr into report mode.
-t: Force mtr to use the curses based terminal interface
-n: Disable DNS (i.e. not try to resolve the host names)