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Re: [Phys-l] IP address



I just learned how to get the current IP address of a computer
connected to Internet. It is simply a matter of using a browser and
typing this URL

http://www.whatismyip.com

For some reason the IP address I got form my Mac (OS-10.3) was not
correct. Is it my Mac only? To get the IP address from my Mac I do
this:

a) select SYSTEM PREFERENCES from the APPLE menu
b) click on the NETWRK icon
c) The IP address appears in the selected line labeled "built in
ethernet."

But that address was not recognized as valid by a server I wanted to
access using the FTP. The address I got from the above URL, however,
was recognized as valid. What causes the discrepancy? Do other Mac
users (OS-10-3 only? Mac only?) have the same IP address by two
methods?

All computer users behind a firewall will see something similar.

You are probably confusing your Mac's real IP address with the address of your gateway. The System Prefs value is your Mac's real IP address, almost certainly a private address in a 192.x.x.x or 10.x.x.x block. If you are behind a firewall of any kind, outsiders will generally see your IP reported as the gateway's, and that is what is reported by whatismyip.com.

Note that various activities you perform on the internet will betray your private IP as well, but not generally with ill effect.

Both IP addresses are "correct". A properly configured firewall, via NAT, *should* make this configuration transparent to you. Private addresses are not publicly routable and that is likely the reason an outside ftp server recognized it as invalid, but it may also indicate a firewall misconfiguration for what you are trying to do. Properly configured, it should not prevent you from doing ftp uploads and downloads, if that was your real question.


Stefan Jeglinski