IPv6

• Unicast
  • 1. Global Unicast Address
  • 2. Unique Local Address (ULA)
  • 3. Link-Local Address
  • 4. Loopback Address
  • 5. Unspecified Address
  • 6. IPv4-Embedded IPv6 Addresses
    • Example Table
• Multicast
  • General Structure
    • Multicast Address Format
  • Flags Field
  • Scope Field
  • Special Multicast Address Types
  • Examples
  • Summary
• Anycast
  • What is an Anycast Address?
  • Key Characteristics
  • IPv6 Anycast Address Examples
  • How Anycast Works
  • Summary Table
• ND, NS, and ULA: The Essentials
  • Summary Table
• Global Unicast Address, GUA
  • Structure of an IPv6 GUA
  • Breakdown of Address Parts
    • 1. Global Routing Prefix (48 bits)
    • 2. Subnet ID (16 bits)
    • 3. Interface ID (64 bits)
  • Allocation Example
  • Key Features
  • Summary Table
• EUI: Calculating IPv6 Interface ID Using EUI-64 from MAC Address 1C-6F-65-C2-BD-F8
  • Step-by-Step EUI-64 Calculation
  • Result
• IPv4 Header Fields vs IPv6 Header Fields
  • Comparison Table: IPv4 vs IPv6 Header Fields
  • Key Differences
  • Visual Summary

Unicast

• One-to-one communication: Data is sent from a single source to a single, specific destination address.
• Typical use: Most internet traffic (web browsing, file downloads) is unicast.
• IPv6 example: Sending a packet from your computer to a specific server.

1. Global Unicast Address

• Publicly routable on the Internet
• Prefix: 2000::/3
• Used for global communication

2. Unique Local Address (ULA)

• Private, not routable on the Internet
• Prefix: FD00::/8
• Used for local communications within a site

3. Link-Local Address

• Valid only within a single local network segment
• Prefix: FE80::/10
• Automatically assigned to every IPv6 interface

4. Loopback Address

• Used by a device to send packets to itself
• Address: ::1/128

5. Unspecified Address

• Indicates the absence of an address
• Address: ::/128

6. IPv4-Embedded IPv6 Addresses

• Allow IPv4 and IPv6 interoperability
• Embed a 32-bit IPv4 address within an IPv6 address, often for transition mechanisms like NAT64, IPv4-mapped, and compatible addresses.
• Common formats:
  • IPv4-mapped IPv6: ::ffff:192.0.2.33 (80 bits zero, 16 bits ones, 32 bits IPv4)
    Used for representing IPv4 addresses in IPv6-only environments, especially in software and NAT64 scenarios
  • IPv4-compatible IPv6: ::192.0.2.33 [deprecated; 96 bits zero, 32 bits IPv4]
  • NAT64/XLAT464: Uses a configurable prefix (e.g., 64:ff9b::/96), followed by the IPv4 address
  • Custom Embedded: Networks can embed IPv4 addresses using various prefix lengths, placing the IPv4 address at specific bits within the IPv6 address

Example Table

Note: Embedding IPv4 in IPv6 addresses is essential for transition and interoperability between IPv4 and IPv6 networks

Multicast

• One-to-many communication: Data is sent from one source to multiple destinations, but only to devices that have joined a specific multicast group.
• Efficient for group communication: Saves bandwidth because the data is only sent once and delivered to all interested receivers.
• Typical use: Streaming media, online conferencing, or network discovery protocols.
• IPv6 example: Sending a video stream to all devices in a multicast group (e.g., all routers on a network).

General Structure

All IPv6 multicast addresses start with the prefix FF00::/8 (the first 8 bits are 11111111 in binary, or FF in hexadecimal).

Multicast Address Format

Example: FF02::1 (All nodes on the local link)

Flags Field

The 4-bit flags field provides additional information about the multicast address:

Scope Field

The 4-bit scope field defines where the multicast is valid:

Special Multicast Address Types

• Solicited-Node Multicast Address: Used by Neighbor Discovery Protocol (NDP). Format: FF02::1:FFXX:XXXX where the last 24 bits come from the unicast/anycast address.
• Well-Known Multicast Groups: Assigned by IANA for specific protocols (e.g., FF02::1 for all nodes, FF02::2 for all routers).

Examples

Summary

• All IPv6 multicast addresses begin with FF.
• The next 4 bits are flags, followed by 4 bits for scope.
• The remaining 112 bits specify the multicast group.
• Scope and flags determine the reach and type of multicast group.
• No broadcast in IPv6; multicast fulfills this role.

Anycast

• One-to-nearest communication: Data is sent from one source to the nearest (in routing terms) member of a group of receivers sharing the same address.
• Used for redundancy and load balancing: Improves availability and performance by routing requests to the closest server.
• Typical use: DNS root servers, content delivery networks (CDNs), and global services like Google DNS.
• IPv6 example: Multiple servers around the world share the same anycast address; a user’s request is automatically routed to the closest server.

What is an Anycast Address?

An IPv6 anycast address is an address assigned to multiple interfaces, typically on different nodes. When a packet is sent to an anycast address, it is routed to the "nearest" interface (according to the routing protocol's metric, such as hop count or cost) that has been assigned that address.

Key Characteristics

• Indistinguishable from Unicast: Anycast addresses are allocated from the unicast address space and look identical to unicast addresses. There is no special prefix or format to distinguish them; their "anycast" property comes from being assigned to multiple interfaces.
• Routing Behavior: Routers deliver packets sent to an anycast address to the closest (in terms of routing distance) node with that address.
• Use Cases: Anycast is commonly used for:
  • Redundancy and load balancing (e.g., DNS root servers, CDN edge nodes)
  • Service discovery and high availability
  • Routing to the nearest gateway or service provider

IPv6 Anycast Address Examples

• Subnet Router Anycast: The lowest address in any IPv6 subnet (where the interface identifier is all zeros) is reserved as the subnet-router anycast address.

For example, in the subnet:

2001:db8:abcd:0012::/64

the anycast address is:

2001:db8:abcd:12::

• Reserved Ranges: The highest 128 interface identifiers in a subnet are also reserved for anycast purposes.

How Anycast Works

1. Assignment: The same unicast address is configured on multiple devices/interfaces.
2. Routing: Each device advertises its route to the shared address. Routers learn multiple paths to the same address.
3. Packet Delivery: When a host sends a packet to the anycast address, the network delivers it to the nearest device (according to the routing protocol).

Summary Table

Note: Anycast addresses provide a way to distribute services across multiple locations, improving redundancy, availability, and response times for clients.

Note: IPv6 does not use broadcast; multicast replaces broadcast functionality.

ND, NS, and ULA: The Essentials

IPv6 ND (Neighbor Discovery), NS (Neighbor Solicitation), and ULA (Unique Local Address) are foundational concepts in IPv6 networking. Here’s a concise breakdown:

IPv6 Neighbor Discovery (ND):

• ND is a protocol in IPv6 that allows devices (nodes) on the same network link to discover each other, learn about routers, resolve Layer 3 (IP) to Layer 2 (MAC) addresses, and maintain reachability information.
• It replaces IPv4’s ARP and ICMP Router Discovery, providing more secure and efficient communication.
• ND uses several ICMPv6 message types, including Neighbor Solicitation (NS) and Neighbor Advertisement (NA), to perform its functions.

Key ND Functions:

• Address resolution (finding a device’s MAC address from its IPv6 address)
• Neighbor reachability detection
• Router and prefix discovery
• Address autoconfiguration (stateless)
• Redirecting hosts to better routes

Neighbor Solicitation (NS):

• NS is a specific message type within ND, used to discover the link-layer (MAC) address of a neighbor or to verify its reachability.
• It is functionally similar to an ARP Request in IPv4 but uses multicast instead of broadcast, making it more efficient.
• NS messages are sent to a solicited-node multicast address derived from the target IPv6 address, ensuring only the relevant device responds.

How it works:

• A host sends an NS message to resolve a neighbor’s MAC address.
• The target device replies with a Neighbor Advertisement (NA), providing its MAC address.
• NS is also used for Duplicate Address Detection (DAD), ensuring no two devices use the same IPv6 address on the network.

Unique Local Address (ULA):

• ULAs are IPv6 addresses meant for local communications within a site or organization, similar to private IPv4 addresses (like 192.168.x.x).
• They are not routable on the global Internet but can be routed within private networks.
• ULA addresses start with the prefix FD00::/8. The rest of the address is generated randomly to ensure uniqueness within the local scope.

Key ULA Points:

• Used for internal-only communication
• Not registered or routed on the Internet
• Replace the deprecated “site-local” IPv6 addresses

Summary Table

These mechanisms are essential for IPv6 networks to operate efficiently, securely, and with minimal manual configuration.

Global Unicast Address, GUA

An IPv6 Global Unicast Address (GUA) is a globally unique, Internet-routable address, equivalent to a public IPv4 address. GUAs are used for devices that need to communicate across the Internet and are assigned by Internet authorities to ensure uniqueness.

Structure of an IPv6 GUA

A typical IPv6 GUA consists of three main parts:

• Prefix: All GUAs start with binary 001 (hex 2 or 3), corresponding to 2000::/3.

Example Address:

2001:0db8:1234:5678:9abc:def0:1234:5678

Breakdown of Address Parts

1. Global Routing Prefix (48 bits)

• Assigned hierarchically (IANA → RIR → ISP → organization)
• Ensures global uniqueness
• Used by routers to forward packets across the Internet

2. Subnet ID (16 bits)

• Allows organizations to divide their address space into multiple subnets
• Functions similarly to subnetting in IPv4, but with more flexibility and scale
• Expressed in hexadecimal notation

3. Interface ID (64 bits)

• Uniquely identifies each interface within a subnet
• Often auto-generated from the device’s MAC address using EUI-64, but can be set manually
• Ensures each device on a subnet has a unique address

Allocation Example

• IANA assigns a large block (e.g., 2001::/16) to a Regional Internet Registry (RIR)
• RIR assigns a smaller block (e.g., 2001:0db8::/32) to an ISP
• ISP assigns a /48 prefix (e.g., 2001:0db8:abcd::/48) to an organization
• Organization subdivides the /48 into multiple /64 subnets using the Subnet ID
• Devices on each subnet get a unique Interface ID

Key Features

• Globally unique and routable: Ensures no address conflicts on the Internet
• Hierarchical allocation: Simplifies routing and address management
• Supports subnetting: Organizations can create many subnets internally
• Large address space: 64-bit Interface ID allows for vast numbers of devices per subnet

Summary Table

In summary:
IPv6 GUAs are globally unique, Internet-routable addresses with a hierarchical structure, enabling scalable, efficient, and conflict-free global networking.

EUI: Calculating IPv6 Interface ID Using EUI-64 from MAC Address 1C-6F-65-C2-BD-F8

Step-by-Step EUI-64 Calculation

1. Split the MAC address into two halves:

   • MAC: 1C-6F-65-C2-BD-F8
   • First half: 1C-6F-65
   • Second half: C2-BD-F8

2. Insert FFFE in the middle:

   • Result: 1C-6F-65-FF-FE-C2-BD-F8

3. Convert to IPv6 notation (grouped by two bytes):

   • 1C6F:65FF:FEC2:BDF8

4. Invert the 7th bit (Universal/Local bit) of the first byte:

   • First byte 1C in binary: 00011100
   • 7th bit (counting from left, zero-based): currently 0
   • Invert it to 1: 00011110 (hex: 1E)
   • So, the new first byte is 1E

5. Final EUI-64 Interface ID:

   • Replace the first byte: 1E6F:65FF:FEC2:BDF8

Result

The interface ID, generated using EUI-64 from the MAC address 1C-6F-65-C2-BD-F8, is: 1E6F:65FF:FEC2:BDF8

IPv4 Header Fields vs IPv6 Header Fields

IPv6 simplifies and streamlines the IP header compared to IPv4, removing or replacing several fields to improve processing efficiency and support new features.

Comparison Table: IPv4 vs IPv6 Header Fields

Key Differences

• IPv6 header is fixed at 40 bytes (IPv4 header is variable: 20–60 bytes).
• Fragmentation fields (Identification, Flags, Fragment Offset) are removed from the main header and handled by an optional extension header in IPv6.
• Header checksum is eliminated in IPv6 to reduce processing overhead.
• Options are replaced by more flexible extension headers in IPv6.
• Flow Label is a new field in IPv6 for special packet handling.
• Address fields are expanded from 32 bits (IPv4) to 128 bits (IPv6).

Visual Summary