IP addressing and subnetting Guide - CCNA CCNP - Networking

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IP Address Classes

Figure 1 IP Classes

 

Private Address Space

Class A 10.0.0.0 to 10.255.255.255

Class B 172.16.0.0 to 172.31.255.255

Class C 192.168.0.0 to 192.168.255.255

 

Default Subnet Masks

Class A 255.0.0.0

Class B 255.255.0.0

Class C 255.255.255.0

 

 

Figure 2 Decimal to Binary conversion

 

 

Figure 3 Binary to Decimal conversion

 

 

Figure 4Network and host identification

 

 

Figure 5 Network Addresses

 

 

Figure 6 Host address identification

 

 

How to determine the number of subnets and the number of hosts per subnet

 

Two formulas can provide this basic information:

Number of subnets = 2S (Second subnet formula: Number of subnets = 2S - 2)

Number of hosts per subnet = 2h - 2

Both formulas calculate the number of hosts or subnets based on the number of binary bits used. For example if you borrow three bits from the host portion of the address use the number of subnets formula to determine the total number of subnets gained by borrowing the three bits. This would be 23 or 2 x 2 x 2 = 8 subnets

To determine the number of hosts per subnet you would take the number of binary bits used in the host portion and apply this to the number of hosts per subnet formula If five bits are in the host portion of the address this would be 25 or 2 x 2 x 2 x 2 x 2 = 32 hosts.

When dealing with the number of hosts per subnet you have to subtract two addresses from the range. The first address in every range is the subnet number. The last address in every range is the broadcast address. These two addresses cannot be assigned to any device in the network which is why you have to subtract two addresses to find the number of usable addresses in each range.

For example, if two bits are borrowed for the network portion of the address you can easily determine the number of subnets and hosts per subnets using the two formulas.

 

 

What about that second subnet formula:

Number of subnets = 2S - 2

In some instances the first and last subnet range of addresses are reserved. This is similar to the first and last host addresses in each range of addreses.

The first range of addresses is the zero subnet. The subnet number for the zero subnet is also the subnet number for the classful subnet address.

The last range of addresses is the broadcast subnet. The broadcast address for the last subnet in the broadcast subnet is the same as the classful broadcast address.

 

 

Figure 7 Class A addressing Guide

 

Figure 8 Class B addressing guide

 

 

Figure 9 Class C addressing guide

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