Configuring Non-NAT (Netgear DG834 -> Netscreen NS5GT)

Posted on 2005-04-13
Medium Priority
Last Modified: 2008-01-09
Hello all,

Apologies if this is more of a hardware question.

We've recently had to swap out a BT ADSL router (5861?) in favour of a new Netgear DG834 ADSL router. During this operation our external IP's supplied by Demon have also changed (don't ask). The new router needs to be configured for Non-NAT and needs to connect to our existing Netscreen NS5GT router/VPN/firewall solution.

The previous BT box had, as far as I'm aware, only the external IP (ie it didn't have one of our internal 10.0.0.X IP's) and this routed straight through to the Netscreen firewall. As I could never look at how the BT box was set up I am a little unsure as to how to configure the DG834 for Non-NAT, straight through routing. I have disabled the NAT option, but still no traffic will pass any further then the Netscreen firewall.

So far I have configured the DG834 to correctly connect to the ADSL (I can ping out from diagnositcs) and I have assigned it the router IP given by our ISP. I have, however, assigned this to both the external and internal addresses, as I was unsure as to how to get the Non-NAT setup passing straight through.

Any guidence would be greatly appreciated!

Question by:tjp6685
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Author Comment

ID: 13773678
I should also mention that I have adjusted the Netscreen settings to reflect the change in external IP that we have undergone - sorry
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Expert Comment

by:Tim Holman
ID: 13775436
Why don't you want to use NAT ?  You're going to have to use it at some point !  :)
If you don't use NAT, then you will need 3 IP address from your ISP - for both interfaces on the Netgear, plus the Netscreen ?  

Author Comment

ID: 13779495
I'm not using NAT because there are several devices that need specific public IP addresses, like our mail server. NAT is enabled on the Netscreen, later on, to deal with the LAN.
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Author Comment

ID: 13806878
I have found that  the non-NAT setup for my new router was in fact correct. It seems that the old Netscreen firewall had frozen. After a couple of reboots and resetting the firewall rules everything is now working again.
LVL 23

Expert Comment

by:Tim Holman
ID: 13810649
It all depends how many IP address you've got to play with.
If you have enough that you can split into two subnets, then you don't need NAT on the outside, but if you've only one or two external IPs, then the only way to get things working would be with NAT.
You can always do double NAT - ie NAT a public address to a private on the external router, and then NAT the private back to a public on the internal router - this is quite a common configuration with ISPs (who should know better !)

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