IPv6 Basics

IPv6 (Internet Protocol version 6) is the successor to IPv4. While IPv4 uses 32-bit addresses (allowing for ~4.3 billion addresses), IPv6 uses 128-bit addresses, providing a virtually infinite number of addresses to accommodate the growing number of devices on the internet.

IPv4 vs. IPv6 Format

• IPv4: 192.168.1.1 (Decimal)
• IPv6: 2001:0db8:85a3:0000:0000:8a2e:0370:7334 (Hexadecimal)

Address Representation & Shortening

IPv6 addresses are written in 8 groups of 4 hexadecimal digits, separated by colons. To make them easier to read, we can use two rules:

1. Omit Leading Zeros

You can remove zeros at the beginning of any block.

2. Double Colon (::)

You can replace one contiguous string of all-zero blocks with a double colon (::). This can only be done once in an address.

IPv6 Communication Types

IPv6 handles data transmission differently than IPv4. The concept of "Broadcast" (sending to everyone) is removed to reduce network noise. Instead, it uses:

Deep Dive: Unicast Address Types

Since Unicast is the most common communication, it has specific address types for different scopes:

1. Link-Local Address (FE80::/10)

This is the most unique feature of IPv6. Every IPv6-enabled interface automatically generates a Link-Local address.

• Range: Starts with fe80.
• Purpose: Communication only within the local network segment (link).
• Routing: Routers do not forward these packets.
• Use Case: Neighbor Discovery Protocol (NDP), Routing Protocol Hello packets (OSPFv3, EIGRP).

2. Global Unicast Address (GUA)

• Range: Starts with 2000::/3 (2xxx or 3xxx).
• Purpose: Public internet communication.
• Routing: Routable globally on the internet (like IPv4 Public IPs).

3. Unique Local Address (ULA)

• Range: Starts with fc00::/7 (Usually fdxx).
• Purpose: Private internal communication.
• Routing: Routable within an organization but not on the public internet (like IPv4 192.168.x.x).

Summary Table