Network+ Exam Cram 2

Without question, the TCP/IP protocol suite is the most widely implemented protocol on networks today. As such, it is a focus on the Network+ exam. To pass the exam, you will definitely need to understand the material presented in this chapter.

This chapter deals with the individual protocols within the protocol suite. The chapter looks at the function of the individual protocols and their purposes. It starts by discussing 76one of the more complex facets of TCP/IPaddressing.

IP Addressing

IP addressing is one of the most challenging aspects of TCP/IP and one that can leave even the most seasoned network administrators scratching their heads. Fortunately, the Network+ exam requires only a fundamental knowledge of IP addressing. The following sections look at how IP addressing works for both IPv4 and the newest version of the IP, IPV6.

To communicate on a network using the TCP/IP protocol, each system has to be assigned a unique address. The address defines both the number of the network to which the device is attached and the number of the node on that network. In other words, the IP address provides two pieces of information. It's a bit like a street name and a house number of a person's home address.

Each device on a logical network segment must have the same network address as all the other devices on the segment. All the devices on that network segment must then have different node addresses.

In IP addressing, another set of numbers, called a subnet mask, is used to define which portion of the IP address refers to the network address and which refers to the node address.

IP addressing is different in IPv4 and IPv6. We'll begin our discussion by looking at IPv4, as IPv6 networks are still few and far between.

IPv4

An IPv4 address is composed of four sets of 8 binary bits, which are referred to as octets. The result is that IP addresses are 32 bits in length. Each bit in each octet is assigned a decimal value. The leftmost bit has a value of 128, followed by 64, 32, 16, 8, 4, 2, and 1, left to right.

Each bit in the octet can be either a 1 or a 0. If the value is 1, it is counted as its decimal value, and if it is 0, it is ignored. If all the bits are 0, the value of the octet is 0. If all the bits in the octet are 1, the value is 255, which is 128+64+32+16+8+4+2+1.

By using the set of 8 bits and manipulating the 1s and 0s, you can obtain any value between 0 and 255 for each octet.

Table 5.1 shows some examples of decimal-to-binary value conversions.

IP Address Classes

IP addresses are grouped into logical divisions called classes. In the IPv4 address space, there are five address classes (A through E), although only three (A, B, C) are used for assigning addresses to clients. Class D is reserved for multicast addressing, and Class E is reserved for future development.

Of the three classes available for address assignments, each uses a fixed-length subnet mask to define the separation between the network and the node address. A Class A address uses only the first octet to represent the network portion, a Class B address uses two octets, and a Class C address uses the first three octets. The upshot of this system is that Class A has a small number of network addresses, but each class A address has a very large number of possible host addresses. Class B has a larger number of networks, but each class B address has a smaller number of hosts. Class C has an even larger number of networks, but each Class C address has an even smaller number of hosts. The exact numbers are provided in Table 5.2.

Subnet Mask Assignment

Like an IP address, a subnet mask is most commonly expressed in a 32-bit dotted-decimal format. Unlike an IP address, though, a subnet mask performs just one function: It defines which parts of the IP address refer to the network address and which refer to the node address. Each of the classes of IP address used for address assignment has a standard subnet mask associated with it. The default subnet masks are listed in Table 5.3.

Default Gateways

Default gateways are the means by which a device can access hosts on other networks for which it does not have a specifically configured route. Most workstation configurations actually just use a default gateway rather than having any static routes configured. Such a configuration is practical because workstations are typically only connected to one network, and thus have only one way off that network.

When a system wants to communicate with another device, it first determines whether the host is on the local network or a remote network. If the host is on a remote network, the system looks in the routing table to determine whether it has an entry for the network that the remote host is on. If it does, it uses that route. If it does not, the data is sent to the default gateway.

In essence, the default gateway is simply the path out of the network for a given device.

IPv6 Addressing

Although IPv4 has served us well for a number of years, it is finally starting to reach its end. The main problem with IPv4 is simply that the demand for IP addresses outweighs what IPv4 is capable of providing. That is where IPv6 comes in.

By far, the most significant aspect of IPv6 is its addressing capability. The address range of IPv4 is nearly depleted, and it is widely acknowledged that we are just at the beginning of the digital era. Therefore, we need an addressing scheme that offers more addresses than can possibly be used in the foreseeable future. IPv6 delivers exactly that. Whereas IPv4 uses a 32-bit address, IPv6 uses a 128-bit address that yields a staggering 340,282,366,920,938,463,463,374,607,431,768,211,456 possible addresses!

IPv6 addresses are expressed in a different format from those used in IPv4. An IPv6 address is composed of eight octet pairs expressed in hexadecimal, separated by colons. The following is an example of an IPv6 address:

42DE:7E55:63F2:21AA:CBD4:D773:CC21:554F

Subnetting

Now that you have looked at how IP addresses are used, you can learn the process of subnetting. Subnetting is a process by which the node portions of an IP address are used to create more networks than you would have if you used the default subnet mask.

To illustrate subnetting, let's use an example. Suppose that you have been assigned the Class B address 150.150.0.0. Using this address and the default subnet mask, you could have a single network (150.150) and use the rest of the address as node addresses. This would give you a large number of possible node addresses, which in reality is probably not very useful. With subnetting, you use bits from the node portion of the address to create more network addresses. This reduces the number of nodes per network, but chances are, you will still have more than enough.

There are two main reasons for subnetting. First, it allows you to use IP address ranges more effectively. Second, it provides increased security and manageability to IP networking by providing a mechanism to create multiple networks rather than having just one. Using multiple networks confines traffic to only the network that it needs to be on, which reduces overall network traffic levels. Multiple subnets also create more broadcast domains, which in turn reduces network wide broadcast traffic.