Getting to Know your IP Address
Getting to know your IP
addresses
The Internet Protocol (IP) was developed in the 1960s
to provide packet fragmentation and reassembly across a packet-switched
network. This packet-switched network became what we now call the Internet.
IP addressing is used to uniquely identify hosts on an internetwork. An
internetwork is made of LANs and WANs that are connected with a router or
routers. To send data from a host on network A to a host on network B, a
logical network addressing protocol must be used. IP is the most popular
logical addressing protocol. However, IPX in the Novell stack and Datagram
Delivery Protocol (DDP) in the AppleTalk stack can also be used. Although
you can find many other types of routed protocols that provide the same
functionality as IP, they aren't as efficient as IP in larger networks.
The dreaded IP address
Before we conquer IP addresses, I want to define some of the terminology
used in this Daily Drill Down:
- Bit: One digit; either one or zero.
- Byte: 8 bits. This term is interchangeable with
octet.
- Octet: 8 bits. This term is interchangeable with
byte.
- Network address: Address with all host bits turned
off.
- Broadcast address: Address with all host bits
turned on.
To fully understand IP addressing, you must be familiar
with binary-to-decimal conversion. To find the decimal equivalent of a
binary number, you must add the binary values. Binary numbers use eight bits
to create a byte. Each bit in the byte has a certain value, and if a bit is
turned on (assigned a value of 1), then the byte takes on that decimal
value. Each bit has a value that starts at 1 and doubles in value from right
to left. Table 1 shows an example of converting a byte to a decimal
value.
Table 1 |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
Decimal value |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
0 |
Binary number |
This table
shows an example of converting a byte to a decimal.
In the above example, there are three bits that are turned on (1s). Add each
of these values to get the bytes decimal value (16+8+2=26). Let's take a
look at another example in Table 2.
Table 2 |
128 |
64 |
32 |
16 |
8 |
4 |
2 |
1 |
Decimal value |
0 |
1 |
1 |
0 |
1 |
0 |
0 |
0 |
Binary number |
In the above
example, there are three bytes that are turned on (64+32+8=104).
The IP address
IP addressing is not hard-coded into a machine. It is known as a
software or logical address because of the way an administrator must
statically configure each host (either manually or with DHCP). The basic
design of an IP address allows hosts on different networks to communicate
with each other, regardless of the type of network on which they are
located.
The IP address is 32 bits long and is divided into dotted decimal. An
example of an IP address is: 10.205.34.2. Each of the decimals is
known as a byte and is 8 bits long. Therefore, an IP address is 4 bytes, or
32 bits long.
An IP address is hierarchal in design and is divided into two parts: network
and host. An IP address not only defines the host on the internetwork but
also describes the network on which the host is located. In the example
above, 10 is the network and 205.34.2 is the host address.
The job of a router is to get packets to a network using the logical
address. To get a packet to a host, the hardware address is used. If a
packet has a destination IP address of 10.205.34.2, the routers in the
internetwork will forward the packet to network 10. If the routing tables do
not have an entry for network 10, the routers will discard the packet.
An IP address can only be configured within certain ranges. Although an IP
address can be displayed in decimal from 0.0.0.0 to 255.255.255.255, only
certain addresses can be used to configure hosts on an internetwork. It is
imperative that you can look at an IP address and know whether it's a valid
host address.
Classes of IP addresses
The original designers of the IP stack came up with a hierarchical
addressing scheme with five ranges, called classes. These ranges are named:
- Class A: IP address range from 0-127 in the first
byte designed for very large companies.
- Class B: IP address range from 128-191 in the
first byte designed for medium-size companies.
- Class C: IP address range from 192-223 in the
first byte designed for small companies.
- Class D: IP address range from 224-239 in the
first byte reserved for multicast addressing. Not used in the public
sector.
- Class E: IP address range from 240-255 in the
first byte reserved for scientific studies. Not used in the public
sector.
Class A
In the four-byte Class A IP address, only the first byte is used to
identify the network. The last three bytes are used to describe the hosts on
each network: network.host.host.host. The Class A range is 0-127 in the
first byte. Only 1-127 can be used to identify Class A networks because 0
and 127 are reserved.
To find the valid host addresses in a Class A network, you must find the
network and broadcast address in the IP range. Since the Class A address
only uses the first byte to identify the network, the last three octets are
host bits.
To find the network and broadcast address, turn off the host bits and then
turn them on again. For example, if we want to use the Class A network
address of 10, the network address, broadcast address, and valid hosts are
determined as shown:
- 10.0.0.0 is the network address because all of the
host bits are turned off (0). The last three octets are zeros because
the first octet is a 10, which is in the Class A range of 1-126.
- To find the broadcast address of the IP address,
turn on the host bits: 10.255.255.255.
- The valid hosts are the numbers in between the
network address and the broadcast address: 10.0.0.1 through
10.255.255.254.
Class B
The Class B range is 128-191. For example, if you find an IP address
that begins with 152, then you know that it's a Class B address. Class B
addresses use the first two bytes to define the network and the last two
bytes to define the hosts on each network: network.network.host.host.
For example, in the IP address 152.93.10.5, 152.93 is the network address
and 10.5 is the host address. In this example, what are the network address,
broadcast address, and valid host range? Remember, all you have to do is to
find the host bits and turn them all off and then turn them all on. In a
Class B address, the host bits are the third and fourth octets by default.
- 152.93.0.0 is the network address (all host bits
off).
- 152.93.0.1 is the first valid host.
- 152.93.255.254 is the last valid host.
- 152.93.255.255 is the broadcast address (all host
bits on).
Class C
In a Class C IP address, only the fourth octet is used to address hosts.
The first three octets are used to define the network:
network.network.network.host.
An example of a Class C address is 200.10.10.59. By glancing at this
address, you can see that the network address is 200.10.10 and the host
address is 59. To find the valid host range, turn all of the host bits off
and then turn them on.
- 200.10.10.0 is the network address because all
host bits are off.
- 200.10.10.1 is the first valid host.
- 200.10.10.254 is the last valid host.
- 200.10.10.255 is the broadcast address because all
host bits are on.
Subnet masks
Subnet masks are used in IP configurations to tell hosts on the network
which part is the network address and which part is the host address of an
IP address. You cannot configure an IP address on a host without also
configuring the subnet mask information.
Remember that a Class A IP address uses only the first byte to describe the
network address and three bytes to describe the host addresses. In a subnet
mask, the network portion consists of all ones (1s) and the host portion is
all zeros (0s). Therefore, a default Class A subnet mask must be 255.0.0.0.
Since the entire first byte is the network portion and must be all 1s, the
decimal value is 255. IP will examine this mask to determine the host and
network bits in an address.
In a Class B IP address, the first two bytes represent the network portion
and the last two bytes are the host portion. Therefore, the default mask is
255.255.0.0.
In a Class C IP address, the first three bytes represent the network portion
and the last byte is the host portion. The default mask is 255.255.255.0.
This is an example of a Class A configuration of a host where 10 is the
network address and 59.135.4 is the host address:
10.59.135.4
255.0.0.0
This is an example of a Class B configuration of a host where 130.59 is the
network address and 135.4 is the host address:
130.59.135.4
255.255.0.0
Here is an example of a Class C configuration of a host where 210.59.135 is
the network address and 4 is the host address:
210.59.135.4
255.255.255.0
The default gateway address is typically configured but is not required. It
is the router address on the network. If no default gateway address is
configured on the host, the host won't be able to communicate outside its
own local network.
Conclusion
In today's computing age, IP addressing is critical in every network. To
become certified in any network program, you must have a fundamental
understanding of IP addressing. If you want a networking job, it's
imperative that you're familiar with IP addressing. You should be able to
determine a valid IP address just by glancing at the IP address and mask. To
do this, you must be able to quickly and efficiently determine what the
network and broadcast addresses are.
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