# Internet Protocol Version 4 (IPv4)
![[Internet Protocol#^g9p613]]
![[Internet Protocol#^1ni8sx]]
A host determines if a packet's recipient is on the same network using its subnet and the recipient's IP address. If the recipient's IP is in the same subnet, the sender and the recipient are in the same network. The host then uses the [[ARP|Address Resolution Protocol]] to find the MAC address of the host, and wraps the packet into a data link layer frame addressed to the recipient's MAC address.
## IPv4 Addressing
Each host using IPv4 uses a 32bit address IP address. Due to the relatively small number of IPv4 addresses, most hosts use private IP addresses that are not globally unique, and are hence not routable on the global internet. To facilitate this gateways use [[NAT|Network Address Translation (NAT)]].
![[NAT#^q2w4u0]]
![[IPv4 - Wikipedia#^x7xy22]]
[[IPv6]] aims to eliminate the need for NAT by using addresses that are much longer (128 bits), allowing each host to have a globally unique address.
The following table lists all reserved IP address blocks, including private networks (defined by RFC 1918). These special address blocks are generally not routable on the public internet.
| Block | Description |
| --------------------------------------------------------------------------- | ---------------------------------------------- |
| 10.0.0.0/8<br>172.16.0.0/12<br>192.168.0.0/16 | Private networks as per RFC 1918 |
| 100.64.0.0/10 | Addresses reserved for carrier-grade NAT |
| 169.254.0.0/16 | Link-local addresses |
| 224.0.0.0/4 | Multicast |
| 127.0.0.0/8 | Loopback addresses |
| 192.0.2.0/24<br>198.51.100.0/24<br>203.0.113.0/24<br>233.252.0.0/24 | Reserved for documentation |
| 0.0.0.0/8<br>192.88.99.0/24<br>192.0.0.0/24<br>198.18.0.0/15<br>240.0.0.0/4 | Reserved for various other purposes |
| 255.255.255.255/32 | Alias for broadcast address of "this" network. |
## IPv4 Subnets
![[IPv4 - Wikipedia#^8ew862]]
![[IPv4 - Wikipedia#^ektegt]]
![[IPv4 - Wikipedia#^x08p6n]]
![[IPv4 - Wikipedia#^gva06v]]
## IPv4 Link-Local Addresses
![[IPv4 - Wikipedia#^fa8ury]]
![[Link-Local Address - Wikipedia#^phb1jc]]
![[Link-Local Address - Wikipedia#^olsw69]]
![[Link-Local Address - Wikipedia#^veckbb]]
![[Link-Local Address - Wikipedia#^l6luwb]]
## IPv4 Multicast
IPv4 multicast is handled by the Internet Group Management Protocol (IGMP).
![[What Is the Internet Group Management Protocol (IGMP)#^n1c9i1]]
![[Multicast Addressing Guide for IP & MAC Multicast Addresses#^9zn1xx]]
![[Multicast#Converting IPv4 Multicast Groups to Multicast MAC Addresses]]