---
id: 08. IPv4 Addressing (Part 2)
aliases: []
tags: []
---

# IPv4 Addressing (Part 2)

## [[IPV4]] address classes


| Class |First octet | numeric range| Prefix Length |
| ----- | ---------- | --------------|    /8        |
| A     |0xxxxxxxx | 0-127           |    /16       |
| B     |10xxxxxxx | 128-191         |    /24       |
| C     |110xxxxxx | 192-223         |              |
| D     |1110xxxxx | 224-239         |              |
| E     |1111xxxxx | 240-255         |              |

## Maximum Hosts per Network

Host portion all 0s = Network address (network ID)
Host portion all 1s = broadcast address 

192.168.1.0/24 -> 192.168.1.255/24
Host portion = 8 bits = 2^8 = 256
Maximum hosts per network = 2^8-2 = 254


172.16.0.0/16 -> 172.16.255.255/16
Host portion = 16 bits = 2^16 = 65,536
Maximum hosts per network = 2^16 -2 = 254

10.0.0.0/8 -> 10.255.255.255/8
Host portion = 24 bits = 2^24 = 16,777,216
Maximum hosts per network = 2^24 -2 = 16,777,214

### Formula 

```
maximum host per network = 2^n-2 
(n=number of hist bits)
```

## First/last usable address

192.168.1.*0*/24 ---------> 192.168.1.*255*/24
00000000                    11111111
00000001                    11111110
192.168.1.*1*/24            192.168.1.*254*/24 
= first usable address      = last usable address

## Cisco router command 


### For all the interface info

```Cisco
R1#show ip interface brief

Interface           IP-address  OK?   Method  Status                Protocol
GigabitEthernet0/0  Unassigned  YES   unset   adminstratively down  down
```

- adminstratively down: Interface has been disabled with the shutdown command
- This is the default Status of Cisco [[router]] interfaces.
- Cisco switch interfaces are NOT administratively down by default
- Status = Layer 1 status (is there a cable) 
- Protocol = Layer 2 status  (is ethernet function conrectly)


### enter the configuration mode for the interface
```Cisco
// shortcut for configuration terminal
R1#conf t
// for configuration of the interface
R1#interface gigabitethernet 0/0
//shortcut
R1#in g0/0
```

### setting the ip adress

```Cisco
R1#ip address 10.255.255.254 255.0.0.0
//enable the interface
R1#no shutdown
// view the change
R1#do show ip interface brief
// shortcut version
R1#do sh ip int br
```

### show interfaces 

to see all the details of the interface

```Cisco
R1#show interfaces g0/0
```

### descriptions of an interface

```Cisco
// see all the description
R1#show interfaces description
// for assigning a description 
// swithc to configuration interface
R1#int g0/0
R1# description ## to SW1 ##
```

## Review

- IPV4 address classes (review clarification)
- Finding the maximum number of hosts, network address, broadcast address, first usable address,
  last usable address of a particular network
- Configuring IP addresses on Cisco device