firewall and port confusion

[UKHicks]

Hi guys,

I have just moved to Cali and signed up with SBC yahoo DSL on the 1.5 to 3 mbit option, and recieved a SPEEDSTREAM 5100 modem. This is hooked up to a switch via a crossover, and there are two clients on the switch. The modem is giving out one ip address via DHCP (i'm guessing its intended for a router/firewall/switch package) and the other is setup on a static ip. Now i'm thinking that just having the windows firewall on right now is leaving my network rather vunerable, hehehe, so i am going to go but the aforementioned package today.

My question is this... there are no options on the modem to configure a firewall, so i am assuming it does not have one built in. However, if i scan the modem with an ip scanner it shows that port 80 is the only port open.... surely if there is no firewall all ports would be open right??? I want to use port 6881 for azureus to download files but its telling me there is a NAT error, and the FAQ says you need to open that port... hmm. What am i missing here? :confused:

Any help is much appreciated.

[Courtney]

Actually, the modem doesn't deal with ports, the computer behind it does. If you are going to use multiple computers on DSL, get a SOHO router, such as a D-Link or Linksys.

courtney sends....

P.S. By the way, the router will include a switch.

[YeOldeStonecat]

Many DSL providers lately have been shipping the install kits with these little "combo" units...a modem (bridge actually), and router, built into one box.

Actually it's a smart move, for many users who don't know about security and what not, they're protected without knowing it.

If you want to use your own router for one reason or another, instead of the built in one, you can usually reconfigure the device into bridged mode only, so now it's working as purely a DSL modem, and you can uplink it to your own router.

Or just open/forward the ports that you need on the Speedstream if you wish to keep it as your NAT router.

Easy way to find out if it's running in NAT mode...on your computer, start==>run==>CMD==>IPCONFIG

If you get a private IP address such as 192.168.1.2, it's running as a router for you already.

[Courtney]

Agreed. However, the Speedstream 5100 is not one of those modems.

The static address the modem receives is to configure the modem itself. Whenever you connect, your ISP uses this address to download modem configurations to your modem (caps are downloaded this way). This happens everytime you reconnect.

The other address is for you. It is configured using the first IP address. This is the address you will use to surf.

This means that if you connect a switch to the Ethernet port on the modem, only the first device will get an IP address. Nothing else will.

The trick is to NAT all addresses in your network to a router that only shows one IP address to the modem. This is where the SOHO router comes in. It allows you to have up to 254 connections on the inside of your network.

By the way, the firewall that comes with XP is actually very good (at least one way). The fact that it allows anything to get out is the problem.

Oh, and make sure you use a standard CAT5 (not a crossover) when connecting a router to the modem. The Speedstream has a standard Ethernet port, not a crossover.

courtney sends....

[YeOldeStonecat]

Agreed. However, the Speedstream 5100 is not one of those modems.

The ones I've worked on are
///checks Efficients website///
http://www.efficient.com/subscriber_networks/5100.shtml
Can work in either mode, unless he gives us a clue like running ipconfig, we don't know how he received it.