Ubuntu / Debian topology change tool CLI

**Drenriza** · March 5th, 2015

Hi all
Is their a command line based tool for Ubuntu / Debian that can show topology changes i a network between a source and destination.
So when a topology change happends (source takes a different path to destination) it prints such info to the terminal screen.

Thanks on advance
Kind regards

**Lars Noodén** · March 5th, 2015

The closest might be traceroute or traceroute6. They operate from the shell but have to be installed explicitly.

**Drenriza** · March 5th, 2015

I tried using

Code:

traceroute --mtu

and

Code:

tracepath

Which i am currently playing around with, thanks for the reply

**Lars Noodén** · March 5th, 2015

You have to point traceroute at a particular target

Code:

traceroute --mtu 8.8.8.8

It won't tell you the topology itself but will give you an idea of the route that those particular packets happened to take on that one occasion.

**Drenriza** · March 6th, 2015

Thanks for the reply Lars

I putted together a small script and are wondering how this can be improved.
Which i have NO doubt it can be

My bash skills is extreamly rusty

Code:

#!/bin/bash

##This script looks for changes in the topology, from a source to a destination target.
##If a change happends it will be printed to the screen of the device that runs the script.

##The script takes two arguments [destination_target], [sleep_between_traceroutes]

if [[ $EUID -ne 0 ]]; then
    echo "This script must be run as root" 1>&2
    exit 1
fi

destination_target=${1}
sleep_between_traceroutes=${2}
run="1"

path1="/tmp/topologyChange1.txt"
path2="/tmp/topologyChange2.txt"

file1="0"

count="0"

echo "script start up"
if [ -e ${path1} ]; then
    rm -v ${path1}
fi

if [ -e ${path2} ]; then
    rm -v ${path2}
fi
while [ ${run} -eq 1 ]
do
    let "count++"
    echo "Script has runned ${count} times"
    if [ ${file1} -eq 0 ]; then
        traceroute -n -I ${destination_target} |awk '{print $2}' |sed '1d' > ${path1}
        file1="1"
    else
        traceroute -n -I ${destination_target} |awk '{print $2}' |sed '1d '> ${path2}        
    fi

    if [ -e ${path1} ] && [ -e ${path2} ]; then
        
        echo "checking topology"    
        if [[ ! $(diff -s ${path1} ${path2}) == "Files /tmp/topologyChange1.txt and /tmp/topologyChange2.txt are identical" ]]; then
            clear
            echo "topology has changed"

            diff -y ${path1} ${path2}

            mv ${path2} ${path1}
        else
            echo "no topology change"
            echo ""
        fi
    
    fi

    sleep ${sleep_between_traceroutes}
done

exit 0

**Lars Noodén** · March 6th, 2015

I see that you could use just awk and do not need sed also. There are several ways to do that. One would be to check if the second column starts with a digit.

Code: