public ip address behind nat

[Lee Johnston]

Hi there,
Basically because NAT is altering all packets leaving on rl0 on your 'nat' 
machine, to the outside world the packets leaving your network, from 'app' 
machine will appear to be from your 'nat' machines external interface.

The way to get around this is to tell natd not to perform NAT on IP 
addresses that are public (i.e. not unregistered addresses as defined in 
RFC1918, so not the 192.168. range and the others).

Easy way to do this is to pass natd the -unregistered_only option. Man page 
for natd explains this a bit better.

You will only be able to route via your 'nat' box if your ISP has routed 
that block of IPs to your external IP on the box.. Hope that makes sense.


Regards,
Lee.



At 18:16 26/01/2005, Mihai Nitulescu wrote:
>Hi all,
>
>Here is what i have done so far.
>
>i worked only on the nat.ex.com
>
>                      internet
>                          |
>                          |
>       ________rl0(193.23143.33)________
>       |                                                    |
>       |         nat.example.com                  |
>       |                                                    |
>       |_______rl1(192.168.0.254)________|
>                                             |
>                                    _____|______
>                                    |___________| switch
>                                            |     |
>             -------------------------------|     |----------------------|
>         LAN 
> _xl0(193.231.43.26)
>                                                            | 
>                 |
>                                                            | 
> app.example.com  |
>                                                            | 
> ________________|
>
>
>
>OK,
>So I created on nat.example.com on rl1 a virtual interface
>ifconfig rl1 alias 193.231.43.25 255.255.255.248
>After that i created a route for this new interface
>route add 193.231.43.25 193.231.43.33 -iface
>
>So now i can ping rl1 rl0 & internet from the app.example.com but i cannot 
>access this machine from the internet.
>
>Any thoughts on that ??
>
>rgds
>
>Mihai
>
>
>
>
>
>
>
>"Thomas M. Skeren III" <tms3 at fskklaw.com> wrote:
>Brian Reichert wrote:
>
>On Mon, Jan 24, 2005 at 03:21:19PM -0800, Mihai Nitulescu wrote:
>
>In the LAN i have the other machine application.example.comI have some 
>Public IP`s from my ISP : 193.231.43.25-30  255.255.255.248 I want to 
>assign to application.example.com 193.231.43.27 and to route this ip 
>trough nat.example.com Any ideea how can i do that ?
>I'm having problems with your setup.  Is Application.example.com at 
>193.531.43.27 or is it on the lan with an internal address?
>
>If it's internal, then machines on the lan can see the internal IP, so 
>there's no reason for it to have a public address.  If machines outside 
>the lan need to get to app.ex.com, then use natd_flags in rc.conf and 
>point the ports you need opened on app to the local addy of app, and use 
>the NAT's external addy for the external users of app.  That would be the 
>easiest way if you don't want to give an external addy to app.
>
>Of course the easiest way is to just give app an external addy and plug it 
>into the ISP supplied router.  Unless app is a M$ box, of course.
>See 'redirect_address' in natd(8).I believe you'll also need to assign 
>your public IPs to the externalinterface of your NAT box.I have a similar 
>setup, but I need to review just what I've doneto make that work...
>
>Please help. Regards, Mihai
>
>
>
>
>
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Lee Johnston, Wildcard Internet

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