IPv4 Addressing (Part-2)| Day-8

• IPv4 classes: Class A range is generally considered as 1-126, with 0 and 127 being reserved. Class B range is 128-191. Class C range is 192-223
• Calculating maximum number of hosts in a network

  1. For Class C network: 2^8 - 2 = 254 hosts

  2. For Class B network: 2^16 - 2 = 65,534 hosts

  3. For Class A network: 2^24 - 2 = 16,777,214 hosts
• Calculating network details

  Network address, broadcast address, first usable address, last usable address
• Maximum number of hosts in a Class A network is 16,777,214
• Host portion is 24 bits, giving 16,777,216 possible addresses
• Formula for determining the number of hosts on a network: 2 to the power of N, minus 2, where N is the number of host bits
• Class A address range: 10.0.0.0/8 through 10.255.255.255
• Network setup includes Class A, Class B, and Class C networks with specific IP addresses assigned to PCs and router interfaces
• Use of 'show ip interface brief' command in the CLI to confirm interface status and IP addresses
• Interface information displayed in the CLI including interface names, IP addresses, and status
• Modern devices won't let you assign invalid IP addresses
• The 'OK?' column is a legacy feature of the command and is not relevant anymore
• 'Administratively down' in the status column means the interface has been disabled with the 'shutdown' command
• Status column

  Considered the Layer 1 status of the interface
• Interfaces currently have no IP addresses assigned, which is considered a valid state
• Method column

  Indicates the method by which the interface was assigned an IP address
• You'll never see an interface with 'down' in the status column and 'up' in the protocol column
• All interfaces are down at Layer 2 because they are down at Layer 1
• Cisco switch interfaces are NOT administratively down by default
• Cisco router interfaces are administratively down by default
• Once interfaces are configured and enabled, both the status and protocol columns should show 'up'
• The 'status' column refers to the Layer 1 status of the interface
• Expect both status and protocol columns to show 'up' after configurations
• The 'protocol' column refers to the Layer 2 status of the interface
• Configuring the gigabitethernet0/0 interface

  Use 'conf t' to enter global config mode, then 'interface gigabitethernet 0/0' to enter interface config mode
• The shortcut version of entering interface configuration mode is 'in'
• You can connect 'gigabitethernet' and 0/0 without a space in the CLI
• Typing 'G 0/0' also works as a short version for gigabitethernet0/0
• Subnet mask

  It is written in dotted decimal format, e.g., 255.255.255.0 for /24
• Short version of gigabitethernet

  • G
  • G0/0
  • G0/1
  • G0/2
• Setting the IP address

  Use the command 'IP address' followed by the IP address
• Interface status changes to up

  Physical layer status and line protocol status both change to up
• Entering interface configuration mode for gigabitethernet 0/0

  Type 'interface' followed by the interface name
• 'no' is used in front of a command to cancel it, e.g., 'no shutdown'
• Cisco router interfaces have the 'shutdown' command applied to them by default
• 255.255.255.0 subnet mask indicates a prefix length of /24
• 255.255.0.0 subnet mask indicates a prefix length of /16
• The interface status and protocol columns show 'up and up' after configuration
• Interface configuration

  1. Enable the interface with 'no shut'

  2. Check the status of the interfaces with 'show ip interface brief'

  3. Configure interface descriptions
• The subnet mask 255.255.255.0 is equivalent to a prefix length of /24