Had a doubt in traceroute command line utility. I was wondering about this thing, when we type in 'www.google.com', my request is sent to the google's server, it's probably processed there and I get millions of results back like in a time frame which is hardly isn't even a second!!! And I also bet there's a lot more going down in there too.
But when we like traceroute packets to www.google.com (I'm not sure whether it's a packet or a bunch of packets), why does it take so much time to show the IP addresses of where it hopped?
Also, when it says 'request timed out', what inference do we get from that?
And my last question is, Dan sir told traceroute in Linux doesn't use ICMP whereas it uses some random high port UDP. I did not get this thing. I'd like it if someone would clarify that and the other questions for me too.
Thank you & also great content ITProTV team, really appreciate that.
Doubt in Traceroute.
@Atharva-Bet great question, the commands tracert, traceroute and mtr all default to using ICMP TIME_EXCEEDED response from each gateway along the path to the host. This done by using the TTL field in the IP protocol header to build a route topology from the source to the destination for instance your example of www.google.com. However, the ICMP protocol can be used for malicious purposes as well, so firewalls with block the ICMP response messages that are being reported by to tracert/traceroute/mtr which will result in the asterisks you see in the output. This will mean one of two possibilities:
1 - The firewall is blocking ICMP request/response messages (if the trace completes)
2 - There is no route to the destination (if the trace fails)
In Dan's case, given the nature of the work he does, he is trying another protocol such as UDP to avoid the firewall just dumping the trace.
I hope this helps.
@wes-bryan Ohh awesome, thanks, sir! Also, one more question here, if one node is blocking the ICMP request/response, does the packet try to hop to some other node just in case to find some other route to the destination? Also, does this hopping have some logic or is it completely random?
@wes-bryan Also sir, I found this on some website - "However, in the Internet, Traceroute messages are often blocked by routers in various Autonomous Systems (AS), making Traceroute highly inaccurate in many cases."
Like I know that but then how much inaccurate exactly? Like is it just of no use in real-time??
@Atharva-Bet on the first question, it just blocks the response, but the TTL is still incremented and continues to the next hop. As for the accuracy, remember this is a simple built-in program to do a general route tracing between source and destination that is the main point for the exam. There are more complex programs that will provide a greater level of the accuracy, however they can be expensive and are rarely built into the operating system.
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