2.2.3-2.2.4 IP Address Space & Subnetting

IPv4 Address Space and Subnetting Part 1

• IPv4 standard created in 1981 using RFC791.
• IPv4 addresses range from 0.0.0.0 to 255.255.255.255, totaling 4,294,967,296 addresses.
• Initially managed by IANA (Internet Assigned Numbers Authority).
• Parts of the address space are now delegated to regional authorities like RIPE, ARIN, and APNIC.
• Public IPv4 addresses are allocated, requiring allocation for use.
• A portion of the address space is private and can be used/reused freely within private networks, business networks, and cloud platforms.
• IPv4 addresses are divided into multiple smaller ranges for specific functions.

Class A Address Space

• Class A address space spans from 0.0.0.0 to 127.255.255.255.
• Class A contains 128 networks, each with 16.7 million addresses.
• Class A networks are represented by 0.anything up to 127.anything; 0.anything is reserved.
• The first octet denotes the network, with the remaining octets for hosts or subnetting.
• Class A addresses were often allocated to very large businesses or organizations who had an internet presence.

Class B Address Space

• Class B address space starts at 128.0.0.0 and ends at 191.255.255.255.
• Class B offers 16,384 networks, each containing 65,536 IP addresses.
• Commonly used for larger businesses that require more addresses than a Class A allocation.
• Addresses are generally allocated to regional authorities.
• Class B networks use formats like 128.0.anything through 191.255.anything.
• In Class B, the first two octets are for the network, and the last two are for assigning to devices or subnetting.

Class C Address Space

• Class C range starts at 192.0.0.0 and ends at 223.255.255.255.
• Class C provides over 2 million networks, with 256 IP addresses each.
• Examples: 192.0.1.anything and 192.0.2.anything
• The first three octets denote the network, with the remainder for hosts or subnetting.
• Class C networks were historically used for smaller businesses.

Class D and E Address Space

• Class D is used for multicast.
• Class E is reserved for later use.

Private IPv4 Addresses

• Private IP addresses are defined in RFC1918, which defines three ranges of IPv4 addresses for internal use.
• Private IP addresses cannot be directly routed across the internet.
• Network Address Translation (NAT) is needed to translate private addresses into public addresses for internet communication.

Class A Private Range

• The Class A private range is a single network from 10.0.0.0 to 10.255.255.255 providing 16.7 million IPv4 addresses.

Class B Private Range

• The Class B private range goes from 172.16.0.0 to 172.31.255.255.
• It consists of 16 Class B networks.
• Each network has 65,536 addresses.
• AWS uses 172.31 as the default VPC range.

Class C Private Range

• The Class C private range is from 192.168.0.0 to 192.168.255.255.
• This range is 256 Class C networks.
• Each network contains 256 addresses.
• This range is generally used within home and small office networks.

IPv4 vs IPv6

• IPv4 has a limitation of 4,294,967,296 addresses.
• IPv6 was created in order to combat IPv4 address exhaustion.
• IPv6 yields 340 sextillion addresses.
• This is equivalent to 670 quadrillion IPv6 IP addresses per square millimeter of the Earth's surface, or 50 octillion IP addresses per human alive today, or 79 octillion IPv4 internets' worth of addressing.

IP Address Subnetting - Part 2

• Subnetting is the process of breaking networks into smaller pieces using Classless Inter-Domain Routing (CIDR).
• CIDR defines the size of a network using a prefix.
• When the prefix value is larger, the network becomes smaller.
• A /8 prefix is the same as the class A network.

Subnetting Example 1

• 10.16.0.0/16 is a range that starts at 10.16.0.0 and ends at 10.16.255.255.
• The /16 indicates that only the first 2 octets are the network.

Subnetting Example 2

• A /16 network is split into two /17 networks.
• The originial network becomes two /17 networks.
• The first subnetwork is 10.16.0.0 through 10.16.127.255 (the halfway point)
• The second subnetwork starts at 10.16.128.0 and extends to 10.16.255.255.
• /16 subnet is equal to two /17 networks.

Subnetting Example 3

• The bottom /17 network can get split into two /18 networks.
• The first /18 subnetwork starts at 10.16.128.0.
• The second /18 network starts at the midpoint.

CIDR Summary

• The entire internet is a /0 network.
• 0.0.0.0, matching the entire internet, is usually a default route.
• /8 is a Class A network.
• /16 is a Class B network.
• /24 is a Class C network.
• /32 is a single IP address.