The term “Bytes” (which sounds like “bites”) was first to used in July 1956 by a PhD at IBM. He spelled it that way to keep typos of “bites” from becoming “bits”. The short answer is that bits measure the amount of data sent on a network, and bytes measure data stored in the computer […]

Classless routing uses a mask, or subnet mask, to define that point where the network portion stops and the host portion starts. The default subnet mask class for class A is 255.0.0.0, which says I have eight bits. The first octet is where the network portion stops. The mask can be defined two ways. One is by spelling it out just as we did here, 255.0.0.0; or there’s a short hand called a sider which just gives you the number of ones in the mask (/8). Either way works just fine.

In IPv4 we have 32 bits divided into 4 octets. Now, of the 32 bits we need to determine where the network portion is and the host portion is, so there’s two pieces to the 32 bit address two ways of defining that. One way is what’s known as classful, and our classes are A, B, and C. The second way is class-less where we use a subnet mask.

We know decimal numbers. We’ve been using those all our lives, so we’re familiar with that. So, if you look at it, our number system is based on the value of where it sits:

Which IP application does the well-known port number 23 reference?

Which address class is set aside for multicast?

Having created a loopback interface and assigned it to an IP address, we want to use it for management purposes, so it must be reachable from other routers and hosts. What we need to do is advertise the loopback’s prefix via our routing protocol(s). This requires “network” statements, interface commands, or route redistributions (“redistribute connected”), […]

Let’s say that we have a router with several interfaces, as shown in Figure 1: Now, imagine that we want to manage our router remotely via Telnet, SSH, SMTP, SDM or some other IP utility. To accomplish this, we’ll have to supply one of our router’s IP addresses to the management software. Let’s say that […]

This time, we’ll take a look at the interaction between network statements, subnet masks and automatic route summarization with RIPv2. To get RIPv2 running on the Fa0/1, Fa0/2 and Fa0/3 interfaces, we’ll use the following configuration: router rip version 2 network 172.16.0.0 network 10.0.0.0 Note that Fa0/1 and Fa0/3 (the network 10.0.0.0 interfaces) are both using […]

Welcome back! In this installment, we’re going to examine VLSM (Variable-Length Subnet Masking, RFC 1878), and how to use the subnetting shortcuts to solve VLSM problems. I’m sure that it won’t surprise you to know that we’ll need the powers of two chart: n = 8 7 6 5 4 3 2 1 2n = 256 […]