On 5/19/24 17:42, Shlomo Solomon wrote:
I teach computer networking and the latest assignment I gave my
students was to use Python and Scapy to emmulate traceroute. The code
is simple:
- send an ICMP packet with TTL = 1 which will fail but return the
first hop address
- continue sending ICMP packets - each time increasing the TTL to get
the next hop
- if the ICMP reply is NOT an error, we have arrived.
None of my student submissions worked, which was strange, so I tried my
own code which I know is correct.
It also did not work.
The error messages arrive for each hop, but it seems that the NO ERROR
message (when the destination is reached) is not arriving.
I also checked with Wireshark and see error replies (as I should) for each
hop, but then (when I assume I have reached the destination) there is
no reply.
I then tried disconnecting my computer from my ISP and connected via a
Hotspot on my phone - PROBLEM SOLVED.
So this seems to be a problem with my ISP (019) blocking some traffic.
But I don't know what the next step is.
If I call customer service, I'm sure no-one will understand what I want.
BTW - ping and the "real" traceroute work fine.
I also looked at router settings, but did not find anything suspicious.
there is your clue - read the source code of traceroute, and see what it
is doing differently.
--guy
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