Re: FN-FORUM: TCP/IP Properties

date posted 2nd February 2007 12:17

Dominic Marsat wrote:
>>> The 255.255.255.255 subnet mask is valid when specifying the
>>> settings for a PPP adaptor, like an ISDN or ADSL modem.
>>> Usually the Gateway address is identical to the IP Address,
>>> though not in the settings you have presented. Enter the same
>>> information into the Gateway field that you entered into the
>>> IP Address field. The subnet mask is set to
>>> 255.255.255.255 to prevent IP access to other equipment on
>>> the network at the remote end of the connection. Give it a whirl, see
>>> what happens. And Dai, sanity not confirmed just yet we'll wait to
>>> hear back.
>>>
>
> I've had a reply from 1&1 support about the strange settings:
>
> "The subnet mask is correct. In order for servers within our network
> to communicate with each other they need to have that subnet mask."
>
> Andrew do you mean these are normal settings for ADSL? I've checked my ADSL
> setup here and on the ADSL port I have a subnet mask of 255.255.255.255.
> That does make sense.
>
> The machine in question is a webserver - part of a much large network. It's
> a really odd way of setting up a machine like this. I've never seen it
> before.
>
> The problem with the subnet mask is that the only IP my server can ever talk
>
> to is its own (212.227.21.59). The gateway is used to talk to any hosts
> that aren't on the same network. Since the gateway is not in the same
> subnet it shouldn't be able to communicate with it!! I think 1&1 have
> strange and complicated routing going on.
>
>
>
>
Erm, erm. OK, I'm gonna' throw my hands up at this one. 1&1 do appear to
be using an uncommon setup and I haven't seen it used in the way that
you describe. I'd expect to find the 255.255.255.255 subnet mask on PPP
adaptors, not computers connected via ethernet or similar.

Presumably the Web server is hosted in a data centre and you connect
remotely using remote desktop, terminal services, VNC, etc. I suspect
they're using NAT or UPnP equipment. The theory goes that, given a
subnet mask of 255.255.255.255, the Web server should not be able to
connect to other computers. Can you actually ping, traceroute, or browse
the Internet from the machine? I can understand 1&1 attempting to
prevent access to computers on a similar network, if only for security
reasons.

I agree, logically the gateway is on a completely inaccessible network.
Perhaps 1&1 can shed a little more light on this puzzling setup.