[luau] Strange find....

[DOUGS at oceanic.com]

> >>Well, there's the imfamouns 10.x.x.x one, which I do 
> believe is your 
> >>cable modem (which oddly enough, acts as a bridge, but 
> still decrements the TTL
> >>and sends back a time exceeded as if it were a router...)   

The cable modem in most cases is a bridge, but the 10-net address that is
the first hop in a trace route is the headend router (CMTS) that is the
gateway.  It's the same interface as the gateway interface your computer
gets with DHCP.  The peculiarities of configuring cable modems with 10-net
addresses so they don't use up publicly routed addressses means it is
primary on the interface and the one returned with a traceroute.

> The impression I got was that it's just a misconfigured 
> bridge :)  Since it's 
> the first hop after your box, and you are using the actual 
> upstream (here it's a 
> 24.x.x.x address, the first IP in our subnet), you aren't 
> actually sending 
> packets to the device at all, so it shouldn't respond with a 
> TTL exceeded (and 
> shouldn't decrement TTL) as if it were a router (because 
> you're not takling to 
> it as a rotuer, and in fact you are in the same IP subnet as 
> the ISP's router). 

No, it is the first hop router, just a different address for the same
interface.  It does exactly the right thing to the TTL.

>   I have no confirmation, but I gather this is the actual IP 
> address the cable 
> modem provider uses for configuration of the device.  
> Telnetting to it gives a 
> rather scary "don't use this" disclaimer, thoguh if you own 
> your cable modem 
> (rather than lease it like I do), this MAY not apply 
> (IANAL!).  I haven't 
> checked, but I wouldn't be surprised if it speaks SNMP.

Your are telnetting to the ISPs router which definitely should have that
scary warning.  The implications if you could succeed are severe.  Since it
is not in fact the cable modem you are telnetting to I hope you heed the
warning.

Hope this has been informative.

-Doug-