Re: What do all those "* * *" mean on a traceroute log?
On Wed, Apr 12, 2023 at 05:37:32PM +0000, Albretch Mueller wrote:
> It is not with every site and it is mostly with one hop.
> $ traceroute google.com
> traceroute to google.com (172.217.0.174), 30 hops max, 60 byte packets
> 1 _gateway (199.83.128.1) 6.687 ms 6.660 ms 6.683 ms
> 2 199.83.240.2 (199.83.240.2) 6.101 ms 6.622 ms 6.610 ms
> 3 ad.nypl.org (199.254.254.1) 6.600 ms 6.588 ms 6.577 ms
> 4 199.254.252.1 (199.254.252.1) 6.566 ms 6.590 ms 6.738 ms
> 5 * * *
> . . .
> 30 * * *
First you have to understand how traceroute works. It's like ping,
except that instead of just sending out a stream of normal packets, one
per second, and noting the reply times, it sends out a bunch of packets
with increasing Time To Live fields.
Each router along the path to the destination decreases the TTL field,
and if it's negative (or zero?) at any given point, that hop is supposed
to return a "Time Exceeded" response. (Time is a badly chosen word here;
it's a hop number, not an actual time interval, that's being counted.)
So, in theory, you should get one Time Exceeded response from each router
along the path. That's what traceroute shows you.
However, some routers may choose not to honor this, and do not send a
Time Exceeded response to you. Or, in some cases, the response packet
may simply be lost in transit. Those are the hops where traceroute
shows * * *.
An example from my system:
unicorn:~$ traceroute www.google.com
traceroute to www.google.com (142.250.190.4), 30 hops max, 60 byte packets
1 routerlogin.net (10.0.0.1) 0.413 ms 0.355 ms 0.415 ms
2 65-131-222-254.mnfd.centurylink.net (65.131.222.254) 38.070 ms 39.776 ms 36.299 ms
3 75.160.81.21 (75.160.81.21) 41.687 ms 45.801 ms 39.873 ms
4 * * *
5 ae0.11.bar2.Toronto1.level3.net (4.69.151.242) 56.715 ms ae14.14.bar2.Toronto1.level3.net (4.69.216.246) 56.550 ms ae0.11.bar2.Toronto1.level3.net (4.69.151.242) 58.637 ms
[...]
No response was received from hop number 4, so traceroute shows me * * *
there.
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