Computrols recommends the use of an inexpensive Cable/DSL Router, in addition to the modem provided by the Internet Service Provider, when connecting CBAS systems to the Internet. This is recommended because it will provide a high level of security against Virus and Hacker attacks. It does this by blocking packets intended for the internal network on all TCP/IP ports, except those specifically forwarded to the computers, programs, or controllers that will accept them.

In order for computers to work with multiple incoming and outgoing network communication packets, the TCP/IP protocol uses thousands of “ports”. Standard programs use specific ports, called “Well Known Ports”. Some examples of Well Known Ports are: port 80/html(Web pages); port 25/smtp(email); port 110/pop(email). CBAS uses some of the ports in the range from port 8750 to 8790. See CBAS Network Architecture for more specifics about CBAS ports.

The router, by default, is set up to allow all outgoing packets. However, most of the time, only port 80 is needed to access the Internet. NAT, or Network Address Translation, is used to disguise or hide the computer accessing the Internet. The router does this by changing the source IP address of the sender to the IP address of the router itself. Thus, the actual sending computer remains anonymous.

The above figure shows the physical configuration of an Internet connection using a router.

It is recommended when purchasing an Internet connection for a CBAS site, that you order a Business DSL w/ static IP address. When setting up the service, call the Internet Service Providers tech support number and get them to either allow you to configure their router, or get them to open the router and turn off NAT. This basically turns the router into a bridge, allowing you to operate with another router inside of that, so that you can have control of port forwarding.

In order to configure a router to allow access to the Internet, you must configure both the WAN interface and the LAN interface. The WAN is the Wide Area Network and the LAN is the Local Area Network. (see figure above)

Configure the WAN interface with the IP address, subnet mask, default gateway, and DNS server address that is provided by the Internet Service Provider. For more information on these terms, see the Network Manual.

The LAN interface usually comes pre-configured with an IP address and subnet mask. However, a computer will have to be configured with the correct IP address in order to access and configure both the LAN and WAN interfaces. Configuration is generally done through a web page based configuration tool on the router itself. Follow the manufacturers instructions to configure the router.

Once you can access the Internet from the computer on the LAN side of the router, you can forward the necessary ports through the router to the correct IP addresses.

Recommended routers:

• Linksys BEFSR11, w/ 1 LAN port
• Linksys BEFSR41, w/ 4 Port switch
• D-Link DI-604, w/ 4 port switch