IP Address Assignments - Basic 2

[bpatters69]

Hello folks,

I am fairly new to the forum and still learning my way around so to speak. I have a pretty basic question but I need to ask it as it will help me greatly.

My question has to do with address asignments, NAT and DHCP. I am trying set up a home network and I just want to clairfy what is going on "behind the scenese" so to speak.

I have a PPoE DSL connection to BellSouth. Hardware-wise, I have a Westell DSL Modem and a Netgear 54Mbps Router. My IP assignment is dynamic so when I start my computer, the first thing my Westell Modem does is grab a Public IP address from my ISP, BellSouth. Once the DSL modem has the public IP address, the DSL modem then issues a private IP to the NetGear router. NAT is the protocol that converts the public IP address to the private IP address.

Since my Netgear Router can also provide NAT and DHCP, my Netgear router takes the private IP that it has been issued from the Westell Modem and issues privte IP addresses via NAT to the PCs that are connected to it. The router provides a firewall functionality to the devices on my LAN. I think the Westell DSL modem does as well but I think the fact that it uses NAT is what Westell defines as a firewall. I could be wrong on this last point.

Sound about right? Anythiing to add or change? Any need to double DHCP and double NAT? If you were to allow only one device to NAT and DHCP, which one would you chose? Router or Modem?

Thanks, Bill

Bill Patterson
Florida

 

[MattWray]

You should be fine as long as you don't want any traffic coming inbound. If you do, then double NATing it will become a problem. Otherwise I don't see any issues with that setup. More security for you home...

Thanks,

Matt Wray

GFH

http://www.sss-steel.com

 

[MaxPipeline]

I generally don't recommend double NAT since each time you use NAT there is a certain amount of overhead involved. It isn't too much, but then again it could have a noticable effect on your percieved bandwidth. Also Mattwray is right. If you ever needed to configure port forwarding (i.e. hosting a webserver or certain online games) then you will have a problem.

On the other hand it is definitely more secure. If I had a choice I would use the Netgear for PPPoE and NAT since it does include a stateful inspection firewall capability which I doubt the Westell does. In fact I have seen it too often where companies consider NAT as a firewall. It most definitely is not, but it is much safer than your PC having a public IP. If you don't notice any performance issues and are do not foresee any need to forward ports onto your private LAN then your setup should work fine. But it is redundant.

 

[bpatters69]

Thanks Matt & Matt,

Follow up question for you. You mention that I am ok as long as I do not need any traffic inbound. I have a Nortel VPN Client that I use on my work PC. I have been able to connect ok but after 10 minutes or so, I get dropped. I wonder if using the NetGear for NAT and disabling NAT on the Westell would stop the drops. I could also set up the NetGear as my PPoE connection.

Your thoughts? Bill

Bill Patterson
Florida

 

[MattWray]

I would definitely bet that the Double-NAT has something to do with it. I would try and configure the box from the ISP as a bridge and use your Netgear for all the routing, etc...

Thanks,

Matt Wray

GFH

http://www.sss-steel.com