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Tomorrow I have a client who needs some help configuring his sonicwall firewall and his 2wire modem. He experienced a temporary power failure which reset the modem back to factory defaults. My question is this - What is the best way to set this up? I have an idea that may or may not be the proper the way.

  • Disable DHCP on 2WIRE modem and enable DHCP on the Sonicwall.
  • Configure 2WIRE with a static IP and configure the Sonicwall to use it as a default gateway.
  • All devices would be on the same subnet.

Does that sound about right??

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I'm wondering to what extent the 2wire can be set up to avoid its meddling. I ideally I'd assume you want a single NAT, and Sonicwall having a public IP address. This can sometimes be accomplished by simply using PPPoE on the Sonicwall, which will turn the 2wire into a transparent bridge with no routing features. Of course, this requires that the ISP actually uses PPPoE.

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This seems to be a proper solution. Further reading suggests that the 2WIRE should be configured in bridge mode with DHCP disabled if you have another routing/filtering device on the same network segment. Thus preventing a double NAT situation. Its funny how so many "business class" ISP packages still ship with these shitty router/modem combos. I think the answer is always opt for a stand alone modem if you have another device handling routing and firewall functions. Thank you cloneman, although I'd still love to hear other views on the matter. – Scandalist Oct 2 '12 at 20:42
If this 2wire is a standard adsl2+ modem (2700 series), replacing it with a simpler device would be wise. ST516 and tplink modems are popular choices, the latter being 25$. Most isps don't force you to use their hardware. Don't throw the 2wire away, they may eventually want it back. You will also need a standalone AP to use wifi behind your firewall. – cloneman Oct 2 '12 at 22:24

I described using using DHCP between the user computers and the SonicWall and using DHCP between the SonicWall and the 2Wire.

You responded with "I guess my main concern is that I don't want 2 DHCP servers dishing out addresses simultaneously. With that said, I am left wondering which device I should set as the default DHCP server."

Maybe you are thinking of setting this up completely differently than I have done. What I have successfully repeatedly and always done with small offices and small routers is


The user computers connect to the LAN ports on the router. Between those computers and router is either DHCP or static addressing. If there is DHCP then there is a DHCP server handling that.

On the other side of the router or firewall device, connected to the WAN port on that device, is a completely different world. If there is DHCP between the WAN port on the router and the modem that has, as far as I know and have seen again and again, nothing to do with what is done on the LAN side of the router. What happens on the far side of the router has nothing more to do with what happens on the near side than than if say Google happens to have DHCP running somewhere, that is invisible and isolated from your LAN side of your network.

Now if you are putting your network together differently, where all your local computers and your SonicWall all hang off the LAN ports on the 2Wire then all these can see all these and you only want one DHCP server. I have never done that because I want nothing to get to the local network without having gone through inspection by the firewall in the router.

Please, try it before you are standing in front of the customer. Get three different brands of routers, each with a different 192.168.x.y admin/setup address, daisy chain all three, set up DHCP between each pair in the chain and verify that this works, just to prove this is correct or to come up with any evidence that there is anything wrong in this.

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Earlier models of some 2Wire often died with spikes or power failures. I replaced dead 2700 three times for one customer before I wouldn't use them any more. It wasn't clear whether this was coming in via the phone line or the power line. 2Wire support knows about this if you press them really hard. 2Wire may have fixed that by now with revised models.

The first thing I would do is direct connect to the 2Wire and really verify it is functioning. And I would put it behind a good Sola filter for both power and phone line that will keep the crud out and the battery backup will avoid power failures in the future. Cheap insurance.

I haven't used SonicWall, but I have one sitting on the shelf somewhere never opened. For small offices with a small router/firewall and a modem I've tried both dhcp between computers and router/firewall and between router/firewall and modem OR static addresssing between computers and router/firewall and between router/firewall and modem. It doesn't really seem to make any difference, other than some people never having seen static addressing before and thinking it must be wrong.

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I guess my main concern is that I don't want 2 DHCP servers dishing out addresses simultaneously. With that said, I am left wondering which device I should set as the default DHCP server. It sounds like before the power failure he had the sonic wall as the DHCP server. It makes more sense to me that you would do the opposite. Configure the 2WIRE modem to set the gateway, addressing and dns info and simply let the Sonicwall filter packets. Yes? No? – Scandalist Oct 2 '12 at 3:23

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