IPv4 Addressing and Address Types

Study Notes

IPv4 addresses have a network portion and a host portion.
Unicast addresses are used in one-to-one communication from one device to another.
The source IP address can only be a unicast address, but the destination address can be a unicast, broadcast, or multicast address.
IPv4 unicast addresses range from 1.1.1.1 to 223.255.255.255.
Broadcast addresses are used for one-to-all communications.
Broadcast packets contain all ones (1s) in the host portion.
Routers don't forward broadcasts by default.
Multicast addresses are used to send packets to a selected group of hosts.
IPv4 multicast addresses range from 224.0.0.0 to 239.255.255.255.
Multicast clients subscribe to receive packets addressed to their allocated multicast address.

### Public and Private IPv4 Addresses

Public IPv4 addresses are globally routed between ISPs and are used on the internet.
Private IPv4 addresses are used for internal network use and are not routable on the internet.
Private addresses are assigned from specific blocks defined in RFC 1918.
Private address ranges are:
- 10.0.0.0/8: Range from 10.0.0.0 to 10.255.255.255
- 172.16.0.0/12: Range from 172.16.0.0 to 172.31.255.255
- 192.168.0.0/16: Range from 192.168.0.0 to 192.168.255.255
Private addresses are sometimes called RFC 1918 addresses.
IPv6 is a long-term solution to the IPv4 address depletion problem.

### NAT

Network address translation (NAT) translates private IPv4 addresses to public IPv4 addresses.
This is typically done on the router connecting an internal network to the ISP network.

Loopback addresses (127.0.0.0/8 or 127.0.0.1 to 127.255.255.254) are commonly identified as only 127.0.0.1.
They are used by a host to direct traffic to itself.
Link-local addresses (169.254.0.0/16 or 169.254.0.1 to 169.254.255.254) are commonly called Automatic Private IP Addressing (APIPA) or self-assigned addresses.
Windows DHCP clients use them for self-configuration when they cannot obtain an IP address through other methods.

IPv4 addresses were assigned using classful addressing as defined in RFC 790.
The three classes were A, B, and C:
- Class A (0.0.0.0/8 to 127.0.0.0/8) - Designed for extremely large networks with more than 16 million hosts.
- Class B (128.0.0.0/16 - 191.255.0.0/16) - Designed for moderate to large networks with up to 65,000 hosts.
- Class C (192.0.0.0/24 - 223.255.255.0/24) - Designed for small networks with a maximum of 254 hosts.
Class D is reserved for multicast, and Class E is reserved for experimental use.
Classful addressing was deprecated in the mid-1990s due to inefficiency.

The Internet Assigned Numbers Authority (IANA) manages and allocates IP addresses.
IANA allocates blocks of IP addresses to Regional Internet Registries (RIRs).
RIRs allocate IP addresses to ISPs, who then provide them to organizations and smaller ISPs.
Organizations can also get their addresses directly from an RIR.

Broadcast domains are network segments where all devices receive broadcast packets.
Switches propagate broadcasts out all interfaces except the one they were received on.
Routers do not propagate broadcasts.
Large broadcast domains can lead to excessive broadcast traffic, which can slow down the network.
Subnetting is used to reduce the size of broadcast domains and improve network performance.
Subnetting divides a network into smaller subnets, creating smaller broadcast domains.
Longer prefix lengths are used to identify subnets.

Subnetting helps manage network devices and services by grouping them into specific subnets.
It improves network performance by reducing broadcast traffic.
It allows administrators to implement security policies by controlling communication between subnets.
It reduces the number of devices affected by abnormal broadcast traffic.