Re: [Ethereal-users] Wierdness in CablemodemLand?

[Guy Harris <gharris@xxxxxxxxx>]

On Sun, Apr 21, 2002 at 10:12:07PM -0700, John E. Mayorga wrote:
> Here is the output of the script:
> 
> traceroute to 24.127.52.1 (24.127.52.1), 3 hops max,
> 38 byte packets
>  1  * * *
>  2  * * *
>  3  * * *

I guess your router isn't sending back the right sort of ICMP packets -
or anything else, for that matter - when it's sent the UDP packet that
the versions of "traceroute" with which I'm familar send, by default.

More recent versions of traceroute can send ICMP ECHO packets
rather than UDP packets to a random port, if you use the "-I" flag.  Try
using "traceroute -I" rather than "traceroute", and see if that makes a
difference.

> traceroute to 24.127.52.2 (24.127.52.2), 3 hops max,
> 38 byte packets
>  1  c-24-127-52-1.we.client2.attbi.com (24.127.52.1) 
> 12.861 ms  8.688 ms  9.804 ms
>  2  c-24-127-52-2.we.client2.attbi.com (24.127.52.2) 
> 36.418 ms  24.211 ms  17.123 ms

*That* is odd, given the routing table you sent.  It should realize that
24.127.52.2 is on the same subnet, and send to it.

> traceroute to 24.127.52.15 (24.127.52.15), 3 hops max,
> 38 byte packets
>  1  c-24-127-52-10.we.client2.attbi.com (24.127.52.10)
>  2990.854 ms !H  2999.486 ms !H  2999.919 ms !H

That's also a bit odd, as I'm not sure why that'd be different from
24.127.52.2 - and I'm not sure why it'd list *your machine* as a route
at all, unless the Linux networking stack is internally faking a Host
Unreachable message due to a failure to get 24.127.52.15's MAC address,
or the mysterious box at 24.127.52.1 is sending back a Host Unreachable
because *it* can't get 24.127.52.15's MAC address, but is putting *your*
IP address as the source address of the reply.

It'd be interesting to see what Ethereal sees when you do

	traceroute 24.127.52.1
	traceroute 24.127.52.2
	traceroute 24.127.52.15

and it'd be interesting to see what "traceroute" prints, and what
Ethereal sees, when you do

	traceroute -I 24.127.52.1
	traceroute -I 24.127.52.2
	traceroute -I 24.127.52.15