IPv4 Addressing - 2

(Updated: )
IT

Overview

  • IPv4 Address Classes (review and clarification)
  • Finding the: maximum number of hosts, network address, broadcast addsress, firstusable address, last usable address (on a particular network)
  • Configuring IP addresses on Cisco Devices
Class First octet First octet numeric range
A 0xxxxxxx 0-127 Usable range is 1 - 126
B 10xxxxxx 128 - 191
C 110xxxxx 192-223
D 1110xxxx 224-239 Reserved for multicast (different from unicast and broadcast)
E 1111xxxx 240-255 Reserved for experimental use

Calculate Maximum Hosts Per Network

Class C
192.168.1.0/24 -> 192.168.1.255/24

  • Host portion = 8 bits = 2^8 = 256
  • 192.168.1.0/24 = network address
  • 192.168.1.255/24 = broadcast address
  • 256 - 2 = 254

Class B
172.16.0.0/16 -> 172.16.255.255/16

  • Host portion = 16 bits = 2^16 = 65,536
  • 172.16.0.0/16 = network address
  • 172.16.255.255/16 = broadcast address
  • Maximum hosts per network = 65,534

Class A
10.0.0.0/8 -> 10.255.255.255/8

  • Host portion = 24 = 2^24 = 16,777,216
  • 10.0.0.0/8 = network address
  • 10.255.255.255/8 = broadcast address
    • Maximum hosts per network = 16,777,214

Maximum host per network = 2^n - 2

First/Last Usable Address

Class C
192.168.1.0/24 -> 192.168.1.255/24

  • First usable address = 192.168.1.1/24
  • Last usable address = 192.168.1.254/24

Class B
172.16.0.0/16 -> 172.16.255.255/16

  • First usable address = 172.16.0.1/16
  • Last usable address = 172.16.255.254/16

Class A
10.0.0.0/8 -> 10.255.255.255/8

  • First usable address = 10.0.0.1/8
  • Last usable address = 10.255.255.254/8

Configuring Cisco Router with IP Address

Create the following configuration using Cisco.

Log in to CLI of R1

1
2
3
4
5
6
7
8
R1>en
R1#show ip interface brief 
/////////////////////


## Layer 1 - "administratively down" -- default status of Cisco ROUTER interfaces. 
## Cisco SWITCH interfaces are NOT administratively down by default
## Protocol - layer 2 status;

  • Status: refers to Layer 1 status
  • Protocol: Layer 2 status

Now to edit the interface – do the following in global configuration mode

  • Now that we are inside the ethernet config, we can assign an IP address to that specific interface.

  • Notice that we must type out the Cisco netmask (and not the slash notation) for this class A network.

  • Also recall that Cisco router interfaces have the “shutdown command” applied to them by default. We disabled that command with no shutdown.

  • do is used to execute a privileged EXEC command from config mode.

  • do sh ip int br = do show ip interface brief

  • The interface configuration is a success.

Let’s do the config for the Gi0/1 interface next.

  • We want the network address is 172.16.255.254 for the router…(?)

  • The network is 172.16.0.0/16. What will the subnet mask be?

  • We can directly switch from one interface to another. Notice how we left off at the previous int g0/0. Now we are in int g0/1

Let’s configure R1 Gi0/2 interface to have an ip address of 192.168.0.254.

  • Given the prefix is /24. The subnet mask should be 255.255.255.0.

Other show commands

  • #show interface : will show way too many interfaces. so it’s important to be specific.

    • specify the interface.
    • GigabitEthernet0/0 is up, line protocol is up.
      • GigabitEthernet0/0 is up : layer 1 is working.
      • line protocol is up : refers to layer 2 status of the interface.

  • #show interfaces description

To configure a interface description: description LINE