Consumer networking head scratcher

William Herrin bill at
Wed Mar 1 19:04:07 UTC 2017

> On Wed, Mar 1, 2017, at 01:23 PM, Aaron Gould wrote:
>> That's strange... it's like the TTL on all Windows IP packets are
>> decrementing more and more as time goes on causing you to get less and
>> less hops into the internet

Hi Ryan,

Windows tracert uses ICMP echo-request packets to trace the path. It
expects either an ICMP destination unreachable message or an ICMP echo
response message to come back. The final hop in the trace will return
an ICMP echo-response or an unreachable-prohibited. The ones prior to
the final hop will return an unreachable-time-exceeded if they return
anything at all.

If the destination does not respond to ping, if those pings are
dropped, or if it responds with an unreachable that's dropped you will
not receive a response and the tracert will not find its end. That's
why you're seeing the "decrementing" behavior you describe.

I have no information about whether comcast blocks pings to its routers.

Bill Herrin

William Herrin ................ herrin at  bill at
Owner, Dirtside Systems ......... Web: <>

More information about the NANOG mailing list