How does traceroute calculate asymmetric routing ?

This was a question i raised a while ago but never ended up getting round to creating an article.

So as we know the basics of traceroute is that it sends out a bunch of UDP packets each packet with a TTL 1 higher then the previous one. When the hop receives the packet and the TTL becomes 0 it sends back a ICMP TTL exceeded and the traceroute has all the information to trace the route.

At the point of the TTL exceeded packet being sent the device sets its TTL to 255 which calculates the amount of hops the packet takes on the way back which allows traceroute to match the UDP TTL to the return ICMP TTL and if they do not match announce an asymmetric route.

Rick Donato

Want to become a networking expert?

Here is our hand-picked selection of the best courses you can find online:
Cisco CCNA 200-301 Certification Gold Bootcamp
Complete Cyber Security Course – Network Security
Internet Security Deep Dive course
Python Pro Bootcamp
and our recommended certification practice exams:
AlphaPrep Practice Tests - Free Trial