weird traceroute

[Nadav Har'El]

On Sun, Jan 31, 2010, Hetz Ben Hamo wrote about "weird traceroute":
> Hi,
> 
> I'm checking something very weird: I'm doing a traceroute to check
> something, and then I see this:
>..
>  7  ten3-1.brdr2.lnd.nv.net.il (212.143.14.134)  115.718 ms  116.122 ms
>  117.610 ms
>  8  10.80.1.1 (10.80.1.1)  143.145 ms  148.781 ms  153.709 ms
>  9  ten4-0.lon.leaseweb.net (195.66.225.56)  113.546 ms  117.951 ms  118.661
> ms
>...
> See line 8. - 10.80.1.1?? I thought that 10.x.x.x wasn't suppose to
> be routable outside internal LAN..
> 
> Am I missing something here?

The host 10.80.1.1 is probably some sort of private gateway that sits between
Netvision's backbone (7) and the London Internet Exchange (9). Both 7 and 9
know how to contact this IP address, but it isn't routable from the general
Internet. You got back a reply from him because *you* are routable so the
reply could reach him. You managed to "find" this host because you (your
traceroute) sent him a UDP datagram with a TTL of 8, causing the packet
to stop at this stage of the route and be returned to you.

-- 
Nadav Har'El                        |      Sunday, Jan 31 2010, 17 Shevat 5770
nyh at math.technion.ac.il             |-----------------------------------------
Phone +972-523-790466, ICQ 13349191 |An apple a day keeps the doctor away. An
http://nadav.harel.org.il           |onion a day keeps everyone away!