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Modem and WIFI DHCP

Last response: in Networking
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April 17, 2011 1:14:47 PM

Hello,
I have a pretty simple (and working) network config, but still I'd like to improve it.

Current Config looks like this:
- modem connected to the ADSL, ethernet interface to the LAN (Pirelli NetGate Voip 2, providing also voice over IP - 192.168.1.1)
- router + WIFI (DLink DSL-2740R) that distributes the "signal" to the LAN at home (192.168.1.251)

the only way I managed to set this up and get it working was to
- swith on the DHSP on the Pirelli
- switch off the DHCP on the DLink
- assign a static IP to the DLink in the same subnet of the Pirelli

in this way the IP address is provided by the Pirelli modem and the packets are just switched by the Dlink.

Now, since the Pirelli DHCP function doesn't allow me to fix the IP associated to a MAC address and this gives me problems, I'd like to improve the overall features by using the DHCP on the DLink. But if I do so, the Default gateway of the network becomes the Dlink and packets don't go to the Pirelli and then to the internet, but are lost in the Dlink (that doesn't know what to do).
Is there a config that can force the Dlink to forward the packets to the Pirelli?

please don't suggest to change the Pirelli router: I know that is an easy solution, but I'm trying to avoid that...

thanks
Simone

More about : modem wifi dhcp

April 17, 2011 2:13:09 PM

Based on the description of your current configuration, I assume you have these routers connected LAN to LAN (not the WAN of the D-Link).

Just because you can't assign static IPs to MAC addresses in the DHCP server of the Pirelli doesn't mean you can use a static IP for the WAN of the D-Link. Every router I've seen allows you to define a static IP on its WAN. Of course you'll want to add the IP address of the Pirelli as the default gateway, properly assign your DNS servers, etc. So now you can hook the routers LAN to WAN (of the D-Link).

April 17, 2011 8:23:37 PM

Hi eibgrad,
thanks for your answer.
I am not sure I understand what you're suggesting.
yes, the Pirelli and the Dlink are connected via Lan and I don't want to change that, mainly because that's the only way I can get them connected to each other.

are you suggesting that I should be able to define a default router on the Dlink? well actually you're right, that's what I should do, but I can't find where to put it...
maybe because, since the dlink is an ADSL modem (even if I don't use the ADSL port on it), is assumes the default route should be the ADSL interface?

simone
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April 17, 2011 11:47:16 PM

just set static ip's on the pc's or use the default dhcp.. dont make it over complicated.
April 18, 2011 12:10:47 AM

selianto said:
Hi eibgrad,
thanks for your answer.
I am not sure I understand what you're suggesting.
yes, the Pirelli and the Dlink are connected via Lan and I don't want to change that, mainly because that's the only way I can get them connected to each other.

are you suggesting that I should be able to define a default router on the Dlink? well actually you're right, that's what I should do, but I can't find where to put it...
maybe because, since the dlink is an ADSL modem (even if I don't use the ADSL port on it), is assumes the default route should be the ADSL interface?

simone


Whenever you chain routers LAN to WAN, you are, by definition, creating a new subnet, with its own DHCP server, firewall, etc., and its own default gateway. It's the responsibility of that router, as the default gateway for its subnet, to navigate its users upstream to the next subnet. If the request is not for the upstream subnet, it's routed up to the default router of that subnet. And so on.

IOW, it all just works. All you have to do is chain them LAN to WAN.

[router a](lan)<-- wire -->(wan)[router b](lan)<-- wire -->(wan)[router c]...

You seem to be suggesting that this doesn't work, which simply can't be the case.

I'm going to speculate what the real problem is here, based on something I just noticed. YOU CAN'T HAVE BOTH ROUTERS USING THE SAME SUBNET!!! That's a big no-no. Because that creates ambiguity. Think about it. For anyone on the D-Link subnet of 192.168.1.x and looking for say 192.168.1.100, is that IP address on the D-Link or the Pirelli?? The answer is, no one knows. It could be either.

Connect your routers LAN to WAN (of the D-Link), but change the D-Link's subnet to something else, say 192.168.2.x. Of course, the D-Link's own IP needs to be in that same subnet as well, so make it 192.168.2.1.
April 18, 2011 12:48:32 AM

a very correct answer.. my answer was based on the fact that I dont know what the purpose of wanting to assign dhcp to mac was.. this kinda defeats the whole purpose of dhcp.

unless me meant mac filtering where only certain ones could connect.

Its pretty easy to set a static ip on a couple computers and be done.

and it just works .

messing around with 2 routers is easy but not so easy to troubleshoot issues if you are a novice and dont know whats happening.
April 18, 2011 7:10:13 PM

eibgrad, thanks for you replies.

still, I can't connect LAN to WAN, mainly because -as I wrote- the WAN interface on the dlink is a PSTN ADSL RJ11 one - not an ethernet RJ45 one.
and there's no ambiguity, now, mainly because the Dlink is now used as a switch, right now, not as a router - so now everything works just fine.

rand_79, thanks for your replies - saying things are easy or that people are a novice is not really helpful...

s
April 18, 2011 7:12:24 PM

btw, as I wrote at the beginning, I am not troubleshooting, I am trying to improve the current config/features
!