NETWORK ADDRESSING
The network address (which is also called the network number) uniquely identifies each network. Every machine on the same network shares that network address as part of its IP address. In the IP address 172.16.30.56, for example, 172.26 is the network address.
The node address is assigned to, and uniquely identifies, each machine on a network. This part of the address must be unique because it identifies a particular machine-an individual-as opposed to a network, which is a group. This number can also be reffered to as a host address. In the same IP address 172.16.30.56, the 30.56 is the node address.
The designers of the internet decided to create classes networks based on network size. For the small number of networks possessing a very large number of nodes, they created the rank class A network. At the other extreme is the class C network, which is reserved for the numerous networks with a small number of nodes. The class distinction for networks between very large and very small is predictably called the class B network.
Subdividing an IP address into a network and node address is determined by the class designation of one's network. Below summarizes the three classes of networks.
Summary of the three classes of networks
8 bits 8bits 8bits 8bits
Class A Network Host Host Host
Class B Network Network Host Host
Class C Network Network Network Host
Class D Multicast
Class E Research
To ensure efficient routing, internet designers defined a mandate for the leading-bits section of the address for each different network class. For example, since a router knows that a Class A network address always starts with 0, the router might be able to speed a packet on its way after reading only the first bit of its address. This is where the address schemes define the difference between a class A, a Class B, and a Class C address. (Class A, B, and C are the only ranges that are used to address hosts in our networks).
Network Address Range: Class A
The designers of the IP address scheme said that the first bit of the first byte in a Class A network address must always be off, or 0. This means a Class A address must be between 0 and 127 in the first byte, inclusive.
Consider the following network address:
0*******
If we turn the other 7 bits all off and then turn them all on, we'll find the Class A range of network addresses:
00000000 = 0
01111111 = 127
So, a Class A network is defined in the first octet between 0 and 127, and it can't be less or more. (Yes, I know 0 and 127 are not valid in a Class A network. I'll talk about reserved addresses in a minute.)
In a Class B network, the RFCs state that the first bit of the first byte must always be turned on but the second bit must always be turned off. If you turn the other 6 bits all off and then all on, you will find the range for a Class B network:
10000000 = 128
10111111 = 191
As you can see, a Class B network is defined when the first byte is configured from 128 to 191.
Network Address Range: Class C
For Class C networks, the RFCs define the first 2 bits of the first octet as always turn on, but the third bit can never be on. Following the same process as the previous classes, convert from binary to decimal to find the range. Here's the range for a Class C network:
11000000 = 192
11011111 = 223
So, if you see an IP address that starts at 192 and goes to 223, you'll know it is a Class C IP address.
Network Address Ranges: Classes D and E
The addresses between 224 to 225 are reserved for class D and E networks. Class D (224-239) is used for multicast addresses and Class E (240-255) for scientific purposes, but I'm not going into these types of addresses (and you don't need to know them).
Network Addresses: Special Purpose
Some IP addresses are reserved for special purposes, so network administrators can't ever assign these addresses to nodes.
Class A Addresses
In a Class A network address, the first byte is assigned to the network address and the three remaining bytes are used for the node addresses. The Class A format is as follows:
network.node.node.node
For example, in the IP address 49.22.102.70, the 49 is the network address and 22.102.70 is the node address. Every machine on this particular network would have the distinctive network address of 49.
Class A IP address can only use the number 1 to 126 to designate Class A network address, Why, because from 1 to 127 of Class A address, the only valid address is 1 to 126 why 127 in a network address is a reserve address for diagnostics which can not be used either.
Class B Addresses
In a Class B network address, the first 2 bytes are assigned to the network address and the remaining 2 bytes are used for node addresses. The format is as follows:
network.network.node.node
For example, in the IP address 172.16.30.56, the network address is 172.16 and the node address is 30.56.
Class B Valid Host IDs
Here's an example of how to find the valid hosts in a Class B network:
- All host bits turned off is the network address: 172.16.0.0
- All host bits turned on is the broadcast address: 172.16.255.255.
The valid hosts would be the numbers in between the network address and the broadcast address: 172.16.0.1 through 172.16.255.254.
Class C Addresses
The first 3 bytes of a Class C network address are dedicated to the network portion of the address, with only 1 measly byte remaining for the node address. Here's the format:
network.network.network.node
Using the example IP address 192.168.100.102, the network address is 192.168.100 and the node address is 102.
Class C Valid Host IDs
Here's an example of how to find a valid host ID in a Class C network:
- All host bits turned off is the network ID: 192.168.100.0.
- All host bits turned on is the broadcast address: 192.168.100.255.
The valid host would be the numbers in between the network address and the broadcast address: 192.168.100.1 through 192.168.100.154.
No comments:
Post a Comment