[standards-jig] Re: My IP Address

Michael Brown michael at aurora.gen.nz
Sun Sep 7 07:49:39 UTC 2003

> Hi Richard!
> Richard Dobson schrieb am 2003-09-02 18:33:08:
> > Yea I agree that the IP address itself is not all that useful when
behind a
> > NAT since you will probably not be able to use it for anything, although
> > is useful if you are just trying to automatically find out if you are
> > a NAT by comparing that IP with the known IP's of your interfaces, i.e.
> > the external IP does not match one of your interface IP's then there you
> > likely behind a NAT.
> If your IP is in one of the following subnets you can expect that you
> are NATed:
>, or for RFC 1918 address space
> or for link local addresses
> If your IP is different from these networks you can expect that you are
> not NATed and that the server will respond with the same IP address. But
> that does not help you very much as you don't know if there is a
> non-NAT firewall.

That's not true.  You could be in a non-Internet connected environment
for example.  The server may be in the same subnet as you.  Also don't
forget that NAT is just not used for sharing home connections.  We have
some mind-blowing NAT configurations at work. (That I don't even
pretend to understand)

> Just from knowing if you are behind a NAT router you do not know which
> file transfers will work for you.

No - this is why knowing your external IP adderss is very handy.


More information about the Standards mailing list