Can I Monitor my LAN, control the usage of the Internet, and Network Resources by other computers from my main computer?
 

In order to monitor, or and Control Network traffic you need to be able to access and control a central point in the network that passes through all of the Network Traffic.

In the case of small Entry Level LANs that would be the Switch on a Cable/DSL Router or an independent switch if a Cable/DSL Router is not used.

Unfortunately Entry Level Routers or Switches are not equipped with the capacity to collect the information, and allow it to be read, and or controlled by one of the Network's computers.

There are few options to control the Network, or shared Internet activities on the Network computers.

Option 1 (The Pro way).

Buy a Managed Switch that can be controlled by software residing on the Server.

 Do not run to look for such a Switch, unless you are ready to spend "big" money. 

Link to: SMC TigerSwitch 6724L2 - Review

Option 2 (The Sneaky way).

A simpler level of control can be achieved by putting Network managing software on the main computer, and client managing software on the rest of the Network's computers.

However,  if the other computers do not belong to you (like in a Dorm Network), people have to agree to put them on.

 Take into consideration that any well-informed person can always disable this software.

There are few shareware programs that could control locally TCP traffic, unfortunately I never found a free one.

Example: NetLimiter - You can use NetLimiter to set download/upload transfer rate.

NetLimiter works well and you can try it for free.

A much "crude" but effective way to control File Download Bandwidth can be achieved by “sabotaging” the TCP RWIN (Receiving Window).

Example: In my computer the optimal setting for TCP RWIN = 256960 Bytes.

 With my Cable Internet connection I get a stable Download of 380KB/sec. 

 Setting the RWIN to 2569 Bytes reduces the stable Download to 12KB/sec. 

You can play with the setting to find a spot that yields low Download, and still maintains decent Surfing Experience. (Probably around 20KB/sec. Download.).

To try adjusting RWIN download this free program: DrTCP

Run the program. It will show the current settings of TCP/IP parameters. Write them down.

You can change any variable that you want, click Apply, and reboot the computer, if no good; you can always change to your original values.

Start with:

MaxMTU -   For DSL - 1492 .  For Cable - 1500 . For ISDN - 1322 . For DialUp - 576

Tcp RWIN - 256960

Window Scaling  - Yes

Time Stamping - No

Selective Acks - Yes

Path MTU Discovery - Yes.

Black Hole - NO

Max Duplicate - 2

TTL - 64

Measure the down load under this condition, and start to reduce the RWIN (you must reboot after each change) and try the download "speed".

Your Mileage May Vary.  Do not complain about the outcome, it is your Call.

Option 3 (The Computer Geek way).

You can eliminate your current Routing system, and use a Central Server (as oppose to the regular peer to peer method used by most Home/SOHO users).

Such a computer is performing similar function as the Cable/DSL Hardware Routers. Many Servers have the capacity to control the distribution to other computers by software setting.

You can Go with Style by using Windows 2003 Server and ISA Firewall.

Link to: HOW TO: Configure a NAT Server in Windows Server 2003.

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