---
id: 07. IPv4 Addressing (Part 1)
aliases: []
tags: 
    - CCNA
---

# IPv4 Addressing (Part 1)

## [[OSI Model]]

- Provides connectivity between end hosts on different networks
(ie. outside of the [[LAN]])
- Provides logical addressing [[IP addresses]]
- Provides path selection between source and destination
- [[Routers]] operate at Layer 3

## IPv4 Header

IP addresses are 32 bits long

Class A
192.168.1.254/24
192.168.1. = network portion  (part of the same network)
254 = host portion (different machine)

Class B
154.78.111.32/16
154.78 = network portion
111.32 = host portion

Class C
12.128.151.23/8
12 = network portion
128.151.23 = host portion

## [[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         |              |


class D are reserverd for Multicast addresses
class E are reserved for expermital 
end of the class A is 126
127 are reserved for loopback addresses

## Loopback addresses

- Address range 127.0.0.0 - 127.255.255.255
- Used to test the 'network stack' (think OSI, TCP/IP model) on local device

## Netmask

Class A: /8   255.0.0.0
Class B: /16  255.255.0.0
Class C: /24  255.255.255.0

Host portion of the address is all 0's = Network Address
the netowrk address cannot be assigned to a host

Host portion of the address is all 1's = Broadcast address Address
The Broadcast address cannot be assigned to a host

## Review

- Network portion / host portion of IPv4 address
- IPv4 classes
- Prefix lengths / netmasks
- Network address / broadcast addresses