Becoming a Protocol Know-It-All
Along with Social Security, home addresses and phone numbers, no other set of digits has so completely permeated our lives like the IP address — four little groups of numbers that make today’s technology possible.
Anyone who has ever set up a DVR, IP camera or even any computer in the past 10 or more years has had to deal in the world of IP, whether you knew it or not. Internet protocol (IP) is one of the biggest reasons we are able to connect these things together in a useful way. In spite of its ubiquitous nature, the IP address is still a very misunderstood, yet necessary part of our toolbox.
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Delivering Data to Destinations
The IP address and its related technologies belong to a group of protocols affectionately called TCP/IP. If that sounds familiar, that’s because TCP/IP is the protocol suite that governs communications on the Ethernet networks we use today, as well as the Internet.
If you just had two computers connected directly together, they would theoretically be able to send data back and forth without too much effort. Each packet of data would be destined for the other machine, and only the other machine.
If you add a third node, there needs to be some way for the network to discern which node a certain packet is destined for. In 1974, the IEEE (Institute of Electrical and Electronic Engineers) came up with the method to do just that.
The TCP/IP protocol suite divides the responsibility of ensuring delivery of data packets to the correct machine across a network into two parts, the Transport Control Protocol and IP. The TCP part of that suite ensures delivery of that data, and is fodder for another column.
The IP in TCP/IP is there to provide a method of getting packets from device to device across the network, and identifying the source and destination addresses of networks.
An IP address is made up of four groups of numbers. In actuality, IP addresses should be seen in binary (all ones and zeros), not as numeric digits. Each group of numbers is actually 8 bits long. Each group is called an octet, because there are 8 bits (1s or 0s) in each.
To really understand IP addressing you will need to get comfortable with binary math. The number 192.168.10.1 would actually be written as 11000000.10101000.00001010.00000001. This is how a computer, switch or router (or network geek) sees an IP address.
Looking at an IP address, we can learn a couple of things. It tells us what the address of the whole network (or subnet) is, as well as the address of a specific device. Well, OK, just looking at an address doesn’t tell all that. You actually need another piece of information, the subnet mask.
Unmasking IP Communication
For an IP router to know how or where to send a packet, it needs to know the source address of the device that sent it. Then, it needs to know if the packet is destined for a different network, and of course, which network it is destined for.
Enter the subnet mask. Here again, if you’ve ever connected a device to a network, you may have been asked to fill in this number. Just like an IP address, the subnet mask is four groups of 8-bit numbers or octets. Unlike an IP address, a subnet mask does not designate a device. It actually tells a router which part of the associated IP address designates the whole network, and which part is for the specific device.
Both of these numbers are necessary for devices to communicate with each other. One of the most common causes for “I got no video” syndrome is two devices with IP addresses not on the same network. Even addresses very close to each other, such as 192.168.10.1 and 192.168.11.2, may be on different networks and can’t talk directly to each other without a router in between.
A router looks at the source IP address and its subnet mask, and does what some would call funny math. It performs an “ANDing” routine. ANDing adds 1s and 0s, but not the same way addition works. Normally, 1 + 1 = 2. With ANDing, 1 and 1 = 1. Remember, binary numbers are made up only of 1s and 0s. After the two numbers are ANDed, the router knows the actual address of the network itself.
The router then performs the same calculation on the destination address and its mask. It will then compare the results of the two calculations and if the source and destination addresses are on different networks, the router forwards the packet. If they are on the same network, the router drops the packet, as the destination device already has the information.
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