IP addressing basics
Feb 1, 2009 12:00 PM, By Brad Gilmer
Maintain critical broadcast networks with IP addressing.
Internet Protocol (IP) addresses take the form xxx.xxx.xxx.xxx, where xxx (an octet) is a number from zero through 255. There are public IP addresses and private IP addresses. Public IP addresses are assigned by the Internet Corporation for Assigned Names and Numbers, and are routable over the Internet. Private IP addresses are not routable over the Internet; they are intended to be used within a facility.
As a broadcast engineer, it is important to understand how this process happens and how to assign addresses logically in your own network.
Private IP addresses
If you are building an internal network, how do you know where to start? Fortunately, early on, the Internet Engineering Task Force (IETF) realized it needed documents to describe how the Internet functions. These documents are known as request for comments (RFCs). A good place to find RFCs is www.rfcs.org. One particularly helpful document is RFC 1918. It sets aside three blocks of IP addresses solely for private networks. These blocks are: 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255 and 192.168.0.0 to 192.168.255.255. Public IP addresses are outside the blocks specified in RFC 1918 and are routable across the Internet.
Introduction to DHCP
When you plug a computer into a local network and it just starts working, how does it get its IP address? How does this new computer not clash with another computer on the network? The answer is found in RFC 2131, which describes Dynamic Host Configuration Protocol (DHCP).
If your computer is set to obtain an IP address automatically when the computer is connected to a network, it begins a series of exchanges with a DHCP server. The server's task is to assign IP addresses according to a predetermined plan established by the network administrator.
The conversation between the DHCP client (your computer) and the DHCP server (the computer responsible for assigning IP addresses) follows a specific pattern. First, your computer sends out a discover message asking DHCP servers to reply with an offer of an IP address. Second, DHCP servers respond to the discover message with an offer message containing an IP address. Third, the client sends a request message back to the DHCP server requesting a specific IP address. Finally, the DHCP server sends an acknowledge message, recognizing the IP address assignment. At a later time, the client may release the IP address when it is no longer needed. (See Figure 1.)
Figure 1. The DHCP negotiation process involves four steps: discover, offer, request and acknowledge. Later, a client may request that an IP address be released.
Manual assignment
In many cases, you will want to manually assign IP addresses. Unfortunately, there is no standardized way of configuring client computers. One of the easiest ways to do this is to use an Internet search engine to find out how to manually set IP addresses for your operating system.
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