Re: NAT addresses - RFC or tradition?

[Grant Taylor <gtaylor@riverviewtech.net>]

On 05/22/07 14:26, Paul Blondé wrote:
> I've noticed that a lot of people use the 192.168.X.X subnet for 
> internal networks, is this (and the less-used 10-series) a 
> requirement of some RFC, or a recommendation that has become 
> tradition?

10.0.0.0-10.255.255.255, 172.16.0.0-172.31.255.255, and 
192.168.0.0-192.168.255.255 are reserved for private (read internal) use 
and guaranteed to not be globally routable.  As others have stated, you 
can use any address you want, though you run the risk of being in 
conflict with some subnet somewhere.  Granted it is VERY unlikely that 
you will effect any one other than your self as the world will route to 
the other subnet, not you.

Please reference RFC 3330 - "Special-Use IPv4 Addresses" 
(http://www.rfc-editor.org/rfc/rfc3330.txt) for more information on 
these and other reserved subnets.

> We are using a completely different subnet, something similar to (for 
> example) 42.127.129.X to further obfuscate the internal network from 
> outside. This, and many other examples, produces a class-A subnet 
> mask (some produce a class-B) when entered in WinXP's TCP/IP dialog, 
> although the actual mask we use with it is class-C.

*nod*

> Is this a no-no? Will it break our server's IPTables when 
> communicating with it? Am I in for a lot of trouble? The addresses 
> don't seem to cause any problems, but I don't want this to jump up 
> and bite us in the bottom sometime down the road.

Well, the 42.x.y.z is not too bad as far as conflicting with someone 
else seeing as how IANA has it "Reserved".  Take a look at the "Internet 
Protocol v4 Address Space" page 
(http://www.iana.org/assignments/ipv4-address-space) on IANA's web site 
for more information.



Grant. . . .