8. IPv4 Addressing Part 2

Maximum Hosts per Network

Class C Network

Consider a Class C network with the IP address range:

• 192.168.1.0/24
  (This range spans from 192.168.1.0 to 192.168.1.255.)

• Host Portion: The host portion in this case is 8 bits (the last octet).

  • Calculation: (2^8 = 256) possible addresses.

• Reserved Addresses:

  • Network Address: 192.168.1.0
  • Broadcast Address: 192.168.1.255

• Usable Hosts:

  • Maximum hosts = (2^8 - 2 = 254) hosts

Class B Network

For a Class B network with the IP address range:

• 172.16.0.0/16 to 172.16.255.255/16

• Host Portion: The host portion here is 16 bits.

  • Calculation: (2^{16} = 65,536) possible addresses.

• Reserved Addresses:

  • Network Address: 172.16.0.0
  • Broadcast Address: 172.16.255.255

• Usable Hosts:

  • Maximum hosts = (2^{16} - 2 = 65,534) hosts

Class A Network

For a Class A network with the IP address range:

• 10.0.0.0/8 to 10.255.255.255/8

• Host Portion: The host portion is 24 bits.

  • Calculation: (2^{24} = 16,777,216) possible addresses.

• Reserved Addresses:

  • Network Address: 10.0.0.0
  • Broadcast Address: 10.255.255.255

• Usable Hosts:

  • Maximum hosts = (2^{24} - 2 = 16,777,214) hosts

General Formula

The general formula to calculate the number of hosts on any network is:

[ \text{Maximum Hosts} = 2^N - 2 ]

Where (N) is the number of host bits.

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First and Last Usable Addresses

Class C Network

For the network 192.168.1.0/24:

• First Usable Address:

  • Increment the host portion by 1:
  • 192.168.1.1/24

• Last Usable Address:

  • Decrement the broadcast address by 1:
  • 192.168.1.254/24

Class B Network

For the network 172.16.0.0/16:

• First Usable Address:

  • Increment the host portion by 1:
  • 172.16.0.1/16

• Last Usable Address:

  • Decrement the broadcast address by 1:
  • 172.16.255.254/16

Class A Network

For the network 10.0.0.0/8:

• First Usable Address:

  • Increment the host portion by 1:
  • 10.0.0.1/8

• Last Usable Address:

  • Decrement the broadcast address by 1:
  • 10.255.255.254/8

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Cisco CLI Device Configuration

Initial Commands

1. Enable Command:

   R1> enable
   R1# show ip interface brief
   

2. Show IP Interface Brief:

   • This command lists interfaces, IP addresses, method of assignment, status, and protocol.

   Fields:

   • Interfaces: Available/connected port interfaces.
   • IP Addresses: Assigned IP addresses.
   • Method: Method used to assign IP addresses.
   • Status (Layer 1): Shows if the interface is administratively down.
   • Protocol (Layer 2): Shows protocol status (cannot be up if Layer 1 is down).

   

Configuring the Interface

1. Enter Configuration Mode:

   R1# conf t
   

2. Select Interface:

   R1(config)# interface gigabitethernet 0/0
   

   • Can be shortened to g0/0.

   

3. Set IP Address and Subnet Mask:

   R1(config-if)# ip address 10.255.255.254 255.0.0.0
   

4. Enable the Interface:

   R1(config-if)# no shutdown
   

Verify Configuration

• Show IP Interface Brief:

  R1(config-if)# do show ip interface brief
  

  • Confirms that the interface is up and running.

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Additional ‘Show’ CLI Commands

1. Show Interfaces:

   show interfaces <interface name>
   

   • Provides detailed Layer 1, Layer 2, and some Layer 3 information.
   • Displays MAC Address (BIA address) and IP Address.

2. Show Interfaces Description:

   show interfaces description
   

   • Allows adding descriptions to interfaces.

   Example:

   R1(config)# int g0/0
   R1(config)# description ## to SW1 ##
   

   • This will display in the description column:

     Interface        Description
     Gi0/0            ## to SW1 ##
     

   

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