Getting public IP address of NAT firewall

Rasjid Wilcox rasjidw at
Fri Feb 8 10:36:36 EST 2002

On Fri, 8 Feb 2002 9:35 am, you wrote:
> Wouldn't a traceroute pick it up?

traceroute to (, 30 hops max, 38 byte packets
 1  smoothwall (  0.881 ms  0.741 ms  0.631 ms
 2 (  17.537 ms  19.016 ms  14.504 ms
 3 (  19.227 ms  14.727 ms  21.189 ms
 4 (  14.496 ms  15.870 ms  17.606 ms
 5 (  28.894 ms  25.816 ms  
24.446 ms
 6 (  25.892 ms  24.447 ms  23.321 ms

Line 2 gives the other end of the ppp link to webone, what I want is this end.

What I'm looking to do is have a cron job that will email me the current IP 
when it changes, and I'm not a big fan for storing passwords in clear text 
files, even if they are only accessible by root.

I'm aware that smoothwall could do this itself, but in the situation 
below (my original post) the hardware firewall cannot.

> At a pinch, the user could DCC send themselves something
> in an IRC channel and see where the packets are going.

Have never really played around with IRC.  But I think a 'traceroute' of a 
packet to myself via the internet would do the trick.  I don't think 
traceroute will do this, although I'm sure there is a tool that will.  (Can't 
see how to do it with nmap.)  I'll have a look at the IRC thing.


> -----Original Message-----
> From: Rasjid Wilcox [mailto:rasjidw at]
> Sent: Thursday, 7 February 2002 11:29 PM
> To: CLUG
> Subject: Getting public IP address of NAT firewall
> Suppose that I have a hardware fireall that does NAT and it is given a
> dynamic IP address by the ISP.  Is there any way for a user of a
> workstation behind the firewall to find out the public IP address of the
> firewall without logging into the firewall?
> What I'm thinking is, is there any information kept in the TCP/IP headers
> that would allow me to do this, or is that all lost during the NAT/IP
> masquarade process?
> Rasjid.

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