IP addresses and modem question

[Dellwood]

Ok, this is how I understand it. If you get a USB modem, plug it in and you get an IP address that's an Internet IP address. You're directly connected to the Internet with that IP or whatever.

My question is, what happens with Ethernet modems. Basically if you plug in your Ethernet modem and plug your computer into it, will you then get your static IP assigned to your computer, or will you have to set up NAT and the modem will have your Internet IP?

The reason I'm curious about this is because I'm thinking of just getting a subnet of IPs and having the machines connected that way. I'm not entirely sure how it would work so if someone could explain it for me, It'd clear things up a lot!

Thanks
-Alex

[CloSeR]

Dellwood,

Ok with an Ethernet Router/Modem, It will be assigned the Internet IP Address.. When you plug your PC into one of the switch ports it will be assigned a DHCP address automatically by the router if it supports DHCP.

So your pc will normally get an address something like 192.168.0.2, and any additional pcs you plug in will get the next addresses in succession... ie 192.168.0.3 and 192.168.0.4

Im using a Netgear DG814, and its an ethernet modem/router with a 4 port switch... all built in. I have 2 pcs plugged into it, and it all just works..

When browsing the Web, both pcs hide behind the one IP Address.. (the ip address of the router), and your router directs traffic to each machine on your internal LAN using NAT.

Hope that all made sense..

Cheers

CLoSeR

[bluedog]

Whether the modem is USB or ethernet is not the issue. In either case the modem itself may take ownership of your public IP address and act as a NAT, or you can have it as a passive modem that doesn't have an address.

It depends on the individual modem's capabilities but is not affected by ethernet or USB. From the perspective of your computer you either have your modem plugged into an ethernet card, or you have it plugged into a simulated ethernet card (which is your USB port with a driver that simulates an ethernet card).

Many people recommend ethernet over USB. One advantage of ethernet is better Linux compatibilty (you never know when you might want to try it), and more future proof-ness with future versions of Windows (because you don't need to upgrade the USB driver). Ethernet is also advantageous if you want to use the ADSL modem as a router. USB tends to only carry say 10 or 11 Mbs (USB 1.1), where ethernet ports will tend to be up to 100 Mbs for your LAN traffic.

[Dellwood]

I see..

The way I saw it was that the packets come in through the modem, which then sends them out it's ethernet port. Each of those packets may be addressed to whatever IP it likes, and when they arrive at the switch, they'll be directed to the appropriate machine, if required. No NAT, just a few machines connected directly to the internet.

A NAT connection is not an option.

I believe this would be similar to having multiple users on Telstra Bigpong cable, where the cable modem is connected to a switch and the individual machines log onto the 'net directly.

[Jonny]

Not quite right

With a Router
You login with the 111.111.111.1 addesss on the router
-----------------------router----------------------------------
ISP Side 111.111.111.1 255.255.255.255
Your Side 222.222.222.2 255.255.255.x
-----------------------------------------------------------------
You assign the 222.222.222.3-x Addesses your side.
And ISP routes anything for 222.222.222.x to 111.111.111.1
All the addresses are visable externally.
---
The way multiusers on Cable works is like having two totally seperate connections (Only you use the same modem) if you don't set it up properly your internal traffic goes through their Cable network. They say it is not charged but you can't really check easily.

I think your getting confused between router and a switch
Have a look at the picture on the bottom ,just ignore the NAT part
http://www.asante.com/support/routerguide/faqs/hardwared.html

PS you should use some type of firewall/block unused ports