[Nottingham] Weird Stuff

Paul Sladen nottingham at mailman.lug.org.uk
Sat Sep 7 17:56:00 2002

On Fri, 6 Sep 2002, Guangyue Liu wrote:

> I've been fooling around with NTL's stuff. i found that when i 
> "ping" on my router, i get two replies, [...]

Yup, one'll be your cable-modem and the one ``running telnetd'' is the UBR
at the head end.  A good deal of network kit doesn't talk SSH for the plain
and simple reason that talking SSH needs more work than talking plain easy
telnet which is just an NVT protocol and of course no encryption overhead.

> So i guess its NTL's router at the other end of the cable modem? but
> when i do a "route -n" on my router i am using 213.xxx.xxx.xxx as the default

Yes;  but your cable modem isn't;  it's using the `'
address you're seeing above.  There are several sets of addresses floating
across the same media;  one lot (the private ones) for the cable modems to
talk to and the other lot (public addresses) for your PC to talk to.  
In the end everything is pointing at the same interface on the same box.

> i guess the 213.xxx.xxx.xxx and one of the 10.xxx.xxx.xxx (the one with
> telnetd) is the same machine. but what the hell is the 80.xxx.xxx.xxx?

It's the /otherside/ of the same machine.

The UBR should have several `' addresses ending `[13579].254'
and all the following addresses bound to the HFC cable interface:

Plus `' and `' bound to the uplink ethernet
(ATM?) interfaces on NTL's side of the Broadband Router.

Have fun, play and enjoy...  urm.  :)

Nottingham, GB