Specifications

Sicon-8 Technical Manual CircuitWerkes, Inc.
83
Using the Sicon-8’s Internal Web Server
Networking basics:
Before reading any further, we would like to mention that the following section is not intended to be a comprehensive guide
to networks, nor does in necessarily describe your network. Indeed, we have found that networks vary quite a lot and
yours will probably be different than is described here. We assume that you, or a network administrator, is familiar with
your network and knows how to set it up to accommodate Web servers that exist within your network. The brief discussion
provided below is only intended to be used as a very non-specific description of how a network might function.
In Internet land, devices on your network get unique IP addresses because each piece of hardware has a serial number
embedded into it. Every device with a serial number, called a MAC address, has to get an IP address assigned to it in
order to function using the networking protocol called TCP/IP, which is what is used for the Internet. The router in your
network uses those IP addresses that it assigns to keep track of what data requests have been made and how to route
responses to the devices that need data. In a way, the IP address is sort of like a nickname that computers use to talk to
each other. A computer will only respond if it has been called by name. So, the IP addresses are what one computer
uses to address or talk to another computer. The router also uses those IP addresses to manage the flow of
communications between each computer so that they are not all talking at once like an old fashioned party-line.
IP addresses are usually doled out within a fixed range, so it's also easier for humans to remember a device's location via
its IP address than to try to remember every item's MAC number. For instance an internal network might use the IP range
of 192.168.1.### where ### can be 001 through 254. Once the network administrator has set up the address range, he
or she only has to keep track of what's assigned to the last three digits of the address range.
Generally, simple networks are divided into two sets of addresses. There are the addresses that exist inside the network
(called the private side) and then there are addresses that exist on the Internet (public) side of the network. We’ve already
described the private side above, but getting stuff on the private side to talk to the public side can be tricky.
When you have one device that is connecting your internal network to the Internet, like a cable modem or DSL modem, it
also has a unique serial number, so it gets assigned an IP address from your ISP. But the ISP only sees the modem, not
other equipment on the inside of your network, so they cannot assign multiple IP addresses (actually they can, but that's
another story). Although you probably only have one IP address, you will have a whole range of port numbers that you
can use for each IP address that exists on the private side of your network. Usually, different types of communications use
standardized ports to talk to devices. For instance http (Web browsing) is mostly done on port 80. FTP is usually port
21. E-mail might use port 25. Often, we want to set our network connection up to pass port 80 to some device on our
network, like the Sicon-8, that serves up web pages. We do that by telling the router/firewall to pass port 80 requests to
the IP address that we know we have previously assigned to the Sicon-8. To do that, we have to tell our firewall that it's
okay to send port 80 requests to the Sicon-8, otherwise it'll just block those requests if they come from the public side of
the firewall. As described earlier, each device on the private side needs a static IP address that is set by the network
administrator. So, each item on the inside of a network that will be communicating with the outside world has to have an
IP address within the local network AND it must also have the appropriate port opened on the firewall. On the Internet
side of the firewall, there is usually only the main IP address and the port number.
When you put it all together it might look like this:
Public IP address 67.234.98.135, port 630 could be mapped to internal IP address 192.168.1.250, port 80. So a browser
request made to 67.234.98.135:630 would serve up a web page because you would really be talking to 192.168.1.250:80.
Once you have that properly configured, your Sicon-8 can serve up Web pages from inside of your network to the Internet.