ADSL modem > router - IP address confusion

Hi all,

I have a working adsl line with 8 static public IP addresses. I currently connect via a Netgear DG834 modem/router, and this works great. The WAN side is manually allocated with one of my IP addresses.

I'd like to use several of my public IP addresses to expose various devices to the Internet. My plan was to replace the DG834 with an ADSL modem, connected to a switch. The switch would then feed several different DMZ devices, and a NAT router which would then feed all the desktop machines.

So I've installed a D-Link DSL-300 modem, a Netgear FS 608 switch, and a Netgear RP 614 NAT router, connected in that order.

The modem works fine - I've configured it with my ISP username and password, and it connects just fine.

The switch also works fine - a PC connected to the switch, set with one of my public IP adresses, is visible to the Internet just fine.

The router is proving to be a *major* headache. When I try to allocate it with the settings I think it should have, it rejects them. More details:

Say one of my public IP addresses is My ISP has informed my that my subnet is, and my gateway is When I try to input these settings for the WAN side of the router, it objects because the gateway is not on the same subnet as the WAN IP address I'm setting it to.

This is very odd, because when I look at my current router, which is running on the same static IP address, it seems to have dynamically obtained the subnet and gateway information that my ISP provided.

What am I doing wrong? Any help much appreciated.

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Thanks for the reply.

The modem control panel doesn't allow setting of its WAN IP address, so presumably it can only accept dynamically assigned IPs.

As far as the modem's LAN IP address, again there appears to be no way to set this - the only IP you can set on the modem is the management IP address; the one on which it runs its built in web server.

Given this, and the fact that I don't want to use DHCP, do I need a diferent modem?

And do you have any comments re. the overall setup? Is this a sensible approach to connecting several devices with public IPs?


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It would have been a lot easier just to use a cheap adsl-router modem that would do all you want in one box -- the Mentor ones with the Alcatel chips set do it very easily and have a 4 ethernet port switch built in or a slightly more complicated but more secure method would be to use a router-modem in bridge mode and use an IPCop box to handle the routing and firewalling and intrusion detection for the orange DMZ and green NAT zones.

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Ernest Bilko

Modem and switch are both layer 2 stuffs, so you do not need to config IP address on them or just config management IP addresses for remote access.

As I understand, you currently manually config a 80.* IP address at the WAN interface of your Netgear DG834, right? I do not know why they gave you a IP address starting with 195.* as your gateway, your gateway should be one of your 8 static IP addresses configed on provider's edge router. Anyway, for your new situation, you just config your new Netgear RP 614's WAN interface by one of your 8 static IP addresses, others can be used for your servers connected with your switch. For gateway configuration. You only need to config the IP address the stuff itself or nothing, because maybe provider use proxy IP tech on its edge router. At the LAN side of your Netgear 614 RP, configing it with the private IP segements like 10.*.*.*/8, 172.16-31.*.*/16 or 192.168.*.*/24 for your use.

If it's still not solved, you must call provider's tech support. I am not very clear for your situation, You must make it clear that the IP segement used between you and your provider, it's 80.*.*.* or 195.*.*.*. I am sorry for my english.

Grunff wrote:

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I have this exact setup working fine with a Netgear modem/router/switch combo. The reason I'm playing around with the separate modem + router is that I want to expose several machines to the WAN, each with its own public IP address. Am I missing something?

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Thanks everyone for your replies. After much fiddling around, I solved the problem by installing a DrayTek router which has a DMZ with ip:ip mapping. Works great.

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Yeah,i see

the isp gives you 8 static ip,and it provide you pppoe connect. so i think Isp add a route with the static ip in its router before you moderm.

think about your network , adsl moderm-->router--->switch

The moderm does pppoe connected.So this moderm is in Nat mode or Route mode now . I think there are two way to solve this problem

1,set one of 8 static ip at your moderm's lan interface.and set your moderm in route mode. In this status ,every pc can set static ip to connect internet. 2,set your moderm at bridge mode.set pppoe username and password in your router.config router static Nat with 8 static address between your lan and moderm. The router can take the pppoe connect.and also take effect in Nat mode.


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