Understand traceroute

hi I'm worried about addresses:
2 172.16.135.129 322.319 ms
3 172.16.135.6 225.354 ms
4 172.16.19.50 87.271 ms

why after exiting my router 192.168.1.1
does the packet enter another network?
Sorry for the question which may be trivial but I can't understand it.
Thank you

That's what packets do, they hop from one network to another.

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Meanwhile, thank you for your reply, 172 is a private address, right?
I expect the packet to come out of my router and be routed to 151.6.180.131

i dont understand why you switch first to a private network which is not part of my lan.

It is. It just looks like it's routed through a few devices within your ISPs internal network before it gets there. It's nothing to worry about.

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Thanks krazeh, i can't retrieve any information on this network, i used nmap but nothing.
Thanks for your support!

As it should be. These are the routers of your ISP. The only thing they do is routing traffic. So you won't be able to find anything with an nmap scan.

Please be also aware about the legal situation of your country. If you perform unauthorized port-scans on other networks than you own, it may is seen as violation.

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Traceroutes are considerably tricker to properly interpret than one typically assumes, here is a link to a document that explains a lot of the issues:
https://archive.nanog.org/sites/default/files/10_Roisman_Traceroute.pdf

Tl;dr:
A) As long as the RTT to the endpoint stays believably sane, large RTTs to intermittent hops are likely caused by either ICMP-rate limiting, ICMP depriorisation, asymmetric paths or all of the above.
B) to properly diagnose path issues it is really helpful to get two traceroute results taken from each ends
C) Traceroute might not be the best tool, try tracepath and especially mtr

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