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Re: [FW-1] web server on secure lan



Actually, you can do this....the router outside the firewall will "turn
it around". I.e., the internally addressed packet leaves the firewall,
is translated, seeks the static NAT'd address (even in the same subnet)
and the next hop outside the firewall, the screening or boundry router
tells it-- hey, go back the way you came for that address. It is turned
around, and enters the firewall, etc, etc.

The only caviat is that this is a very slow process, and some services
may on occasion time out. We used to do this with 130 internal pop/smtp
mail servers, belonging to different internal entities, all NAT'd to the
outside world. However, when they communicated with each other, they did
the MX lookup on the DNS, and tried to go out to the internet and thus
were turned around. Fortunately, we came to our senses, and implemented
a "split-brain" DNS which resolved the internal servers to internal
addresses. Much more reliable.

Bob

-----Original Message-----
From: Hal Dorsman [mailto:[email protected]]
Sent: Friday, June 14, 2002 3:33 PM
To: [email protected]
Subject: Re: [FW-1] web server on secure lan

If you want to route back into the same interface you came out
of you can't do it.  You can route from a hide Nat'ed LAN to a
legal IP which is statically routed to in internal host in a
separate DMZ on a difference interface.

Hal

> -----Original Message-----
> From: Russell Washington [mailto:[email protected]]
> Sent: Friday, June 14, 2002 12:16 PM
> To: [email protected]
> Subject: Re: [FW-1] web server on secure lan
>
>
> I don't think it's possible.  Presume a ping, for example.
> You should (I
> think) get the following sequence of events.
>
> - Ping from: Internal Address X to Public Address Z;
>
> - Inbound (to FW) packet passes security policy, gets sent to
> OS for routing
> decision;
>
> - Routing tables say "packet is bound for address on external
> interface
> (whether part of subnet or not), send it to that NIC and out the door;
>
> - Outbound (from FW) packet passes security policy;
>
> - NAT is performed on destination address, so now ping looks
> like Internal
> Address X to Internal Address Y;
>
> - Packet gets shoved out of external interface with
> destination of Internal
> Address Y;
>
> - Packet gets either ignored by all devices on the external
> subnet (if web
> server public IP is on that subnet) or dropped by some
> upstream-to-the-Internet router, having been shoved out of
> the external NIC.
>
> I haven't done any sniffing to verify the above, but I think
> that's how it
> would work (or, in your case, not work for your techs).
>
> -----Original Message-----
> From: Richard Marshall [mailto:[email protected]]
> Sent: Friday, June 14, 2002 8:56 AM
> To: [email protected]
> Subject: [FW-1] web server on secure lan
>
>
> Hi,
>
> I'm after some advice/confirmation.
>
> I have had to setup a test environment webserver on an
> internal lan with a
> NAT to a public IP. Public access now works without problem
> (thanks to some
> pointers from this list).
>
> However, the tech guys that have requested the test env.
> requested that they
> should be able to access the public natted ip themselves.
> i.e. out from the
> lan via a hide address and back into the lan via the nat
> address of the
> webserver. I was sceptical that it was possible (and am not
> sure why they
> feel it's necessary). Having spent the day trying every
> combination of nat
> rules, static routes, etc. that I can think of I have come to
> the conclusion
> it's not possible.
>
> Am I right in thinking this, or is it possible after all?
>
> I am running fw-4.1 sp3 on nokia (it's a distributed
> environment, but it is
> only the lan behind the firewall in question that can't
> access the public IP
> address.)
>
> thanks in advance
>
> rich
>
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