Short-circuited traceroutes on FIOS
Rob Foehl
rwf at loonybin.net
Wed Dec 11 04:48:48 UTC 2019
On Tue, 10 Dec 2019, Joe Maimon wrote:
> Anyone have an idea why there are some destinations that on residential
> verizon fios here in NY area terminate right on first external hop?
They're returning fake ICMP echo replies from their BNGs for echo packets
with TTL=1, thus any ICMP traceroute (Windows and mtr by default, etc.)
seems to terminate at their layer 3 edge. UDP/TCP traceroute are
unaffected, ICMP works fine if you set the initial TTL to n+1 where n is
the hop that's lying.
Support claims that it was a mistake, but it's also been 15+ months and
it's pretty deliberate behavior. Draw your own conclusions...
-Rob
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