IPv6 (Internet Protocol Version 6)

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IPv6 (Internet Protocol Version 6) 

1. Introduction to IPv6

  • IPv6 stands for Internet Protocol Version 6. It is a Network Layer (Layer 3) protocol used to provide addressing and routing for devices connected to an IP network.
  • IPv6 was developed mainly to overcome the limited address space of IPv4 and to support the continued growth of the Internet.

Basic Diagram

              IPv6 NETWORK

┌──────────────┐
│   Computer   │
│ 2001:db8::10 │
└──────┬───────┘
       │
       │ IPv6 Packet
       ▼
┌──────────────┐
│    Router    │
│ IPv6 Router  │
└──────┬───────┘
       │
       │
       ▼
┌──────────────┐
│    Server    │
│ 2001:db8::20 │
└──────────────┘

  • The router uses the destination IPv6 address to forward the packet toward the destination network.

2. IPv6 Address

  • An IPv6 address is 128 bits long.
  • It is normally represented as eight groups of 16 bits, written in hexadecimal and separated by colons (:).

IPv6 Address Structure

                         128 Bits
┌──────┬──────┬──────┬──────┬──────┬──────┬──────┬──────┐
│ 16b  │ 16b  │ 16b  │ 16b  │ 16b  │ 16b  │ 16b  │ 16b  │
└──────┴──────┴──────┴──────┴──────┴──────┴──────┴──────┘

  2001 : 0db8 : 0000 : 0000 : 0000 : ff00 : 0042 : 8329

Example

2001:0db8:0000:0000:0000:ff00:0042:8329

Each group contains 4 hexadecimal digits, representing 16 bits.

3. IPv6 Address Shortening

IPv6 provides rules for shortening addresses.

  • Rule 1: Leading zeros can be removed

0db8 → db8
0042 → 42

Therefore:

2001:0db8:0000:0000:0000:ff00:0042:8329

can become:

2001:db8:0:0:0:ff00:42:8329

  • Rule 2: Consecutive zero groups can be replaced by ::

2001:db8:0:0:0:ff00:42:8329

can be written as:

2001:db8::ff00:42:8329

Important: :: should normally be used only once in an IPv6 address.

4. IPv6 Address Structure

An IPv6 address can be logically divided into:

┌───────────────────────────────┬──────────────────────┐
│       Network Prefix          │    Interface ID      │
└───────────────────────────────┴──────────────────────┘
             64 bits                    64 bits

A common IPv6 subnet uses a /64 prefix.

For example:

2001:db8:1234:5678:abcd:ef01:2345:6789
└───────────────┬───────────────┘
       Network Prefix
           64 bits

                         └───────────────┬───────────────┘
                                  Interface ID
                                     64 bits

5. Types of IPv6 Addresses

IPv6 has three main address types.

A. Unicast

  • A Unicast address identifies a single interface.

Communication is:

One → One

PC ─────────────────► Server
       Unicast

B. Multicast

  • A Multicast address identifies a group of interfaces.

Communication is:

                 ┌──► PC 1
                 │
Server ──────────┼──► PC 2
                 │
                 └──► PC 3

                Multicast

  • One sender can send data to multiple receivers that belong to the multicast group.

C. Anycast

  • An Anycast address can be assigned to multiple interfaces. 
  • Routing delivers the packet to one appropriate destination, typically the nearest according to the routing topology.

                 ┌──► Server 1
                 │
Client ──────────┼──► Server 2
                 │
                 └──► Server 3

                  Anycast

6. IPv6 Does Not Use Broadcast

  • One important difference from IPv4 is that IPv6 does not use broadcast.

Instead, IPv6 uses mechanisms such as:

  • Multicast
  • Anycast

for communication patterns that do not require ordinary unicast.

7. IPv6 Packet Format

An IPv6 packet consists of:

┌─────────────────────────────────────┐
│          IPv6 Base Header           │
│              40 Bytes               │
├─────────────────────────────────────┤
│        Extension Header(s)          │
│             Optional                │
├─────────────────────────────────────┤
│              Payload                │
│               Data                  │
└─────────────────────────────────────┘

The IPv6 base header is fixed at 40 bytes.

8. IPv6 Header

  • The important fields of the IPv6 header are:

┌──────────────────────────────────────────────┐
│ Version │ Traffic Class │                    │
├─────────┴────────────────────────────────────┤
│              Flow Label                      │
├──────────────────────┬───────────────────────┤
│ Payload Length       │ Next Header           │
├──────────────────────┴───────────────────────┤
│              Hop Limit                       │
├──────────────────────────────────────────────┤
│          Source Address (128 bits)           │
├──────────────────────────────────────────────┤
│       Destination Address (128 bits)         │
└──────────────────────────────────────────────┘

Important Fields

  • Version: Indicates the IP version. For IPv6, the value is 6.
  • Traffic Class: Used for traffic classification and handling.
  • Flow Label: Helps identify packets belonging to a particular flow.
  • Payload Length: Specifies the length of the payload following the IPv6 base header.
  • Next Header: Identifies the next header, such as an extension header or transport protocol.
  • Hop Limit: Limits the number of routers a packet can pass through.
  • Source Address: IPv6 address of the sender.
  • Destination Address: IPv6 address of the receiver.

9. IPv6 Communication

             SOURCE                         DESTINATION

       ┌──────────────┐                 ┌──────────────┐
       │      PC      │                 │    Server    │
       │ 2001:db8::10 │                 │ 2001:db8::20 │
       └──────┬───────┘                 └──────▲───────┘
              │                                │
              │         IPv6 Packet            │
              ▼                                │
       ┌──────────────┐                 ┌──────┴───────┐
       │   Router 1   │──────► Router 2 ─►│ Destination │
       └──────────────┘                 └──────────────┘

  • The routers examine the destination IPv6 address and forward the packet toward the appropriate network.

10. IPv6 Auto-Configuration

  • IPv6 supports SLAAC (Stateless Address Autoconfiguration).
  • SLAAC allows a host to automatically configure an IPv6 address in suitable network environments.

             Router
                │
                │ Router Advertisement
                ▼
          ┌────────────┐
          │  Computer  │
          └─────┬──────┘
                │
                ▼
        IPv6 Address
         Configured

  • IPv6 can also use DHCPv6 when required.

11. Neighbor Discovery Protocol (NDP)

  • IPv6 uses Neighbor Discovery Protocol (NDP) for discovering and interacting with neighboring nodes on the local link.
  • NDP is based on ICMPv6.

It can help with:

  • Neighbor discovery
  • Router discovery
  • Address resolution
  • Neighbor reachability detection
  • Address configuration support

In IPv4, ARP is commonly used for address resolution. IPv6 uses NDP instead of ARP.

12. Advantages of IPv6

1. Huge Address Space

  • IPv6 uses 128-bit addresses.
  • The theoretical address space is of 2¹²⁸
  • This provides an enormous number of possible addresses.

2. Simplified Base Header

  • The IPv6 base header has a fixed size of 40 bytes.

3. No Broadcast

  • IPv6 eliminates broadcast and uses multicast/anycast where appropriate.

4. Auto-Configuration

  • IPv6 supports automatic address configuration through mechanisms such as SLAAC.

5. Efficient Multicast Support

  • Multicast is an important part of IPv6 communication.

6. Suitable for Large Networks

  • The huge address space makes IPv6 suitable for large-scale networks, including modern Internet and IoT deployments.

13. Why Was IPv6 Developed?

The major limitation of IPv4 is its 32-bit address space.

                  IPv4
                    │
                    ▼
                 32 bits
                    │
                    ▼
          Limited Address Space
                    │
                    ▼
             More Devices
                    │
                    ▼
                  IPv6
                    │
                    ▼
                128 bits
                    │
                    ▼
          Huge Address Space

As the number of Internet-connected devices increased, the availability of IPv4 addresses became a major issue. IPv6 provides a vastly larger address space.

14. Example of IPv6 in a College Network

Suppose a college has several computers and a server:

                 COLLEGE IPv6 NETWORK

       ┌─────────────────┐
       │   Computer 1    │
       │ 2001:db8:1::10  │
       └────────┬────────┘
                │
         ┌──────▼──────┐
         │   Switch    │
         └──────┬──────┘
                │
         ┌──────▼──────┐
         │    Router   │
         │ 2001:db8:1::1│
         └──────┬──────┘
                │
         ┌──────▼──────┐
         │    Server   │
         │ 2001:db8:1::20│
         └─────────────┘

The computer can send an IPv6 packet to the server using the server's IPv6 address as the destination address.

15. IPv6 vs IPv4 — Important Comparison



16. Quick Revision Diagram

                         IPv6
                          │
              ┌───────────┴───────────┐
              │                       │
          128-bit Address          Layer 3
              │                       │
       Hexadecimal Format          Routing
              │
      ┌───────┼────────┐
      │       │        │
   Unicast Multicast Anycast
      │
      └─────────────────────┐
                            │
                     No Broadcast
                            │
                 ┌──────────┴──────────┐
                 │                     │
               SLAAC                  NDP
          Auto Configuration    Neighbor Discovery

Exam Definition

  • IPv6 (Internet Protocol Version 6) is a 128-bit Network Layer protocol that provides addressing and routing for IP networks. 

  • It was developed primarily to provide a vastly larger address space than IPv4 and includes features such as multicast, SLAAC, and Neighbor Discovery Protocol (NDP).

Key point to remember:
IPv4 = 32-bit address
IPv6 = 128-bit address

Advantages of IPv6

  • Realtime Data Transmission: There is very little latency in the transmission of data. For instance, live broadcasting of sporting events with a five to six second lag.
  • IPv6 authentication verifies that data is authentic and hasn't been tampered with. For instance, utilizing hash values to verify messages.
  • IPv6 Encryption: Provides inherent security by encrypting communications at the network layer even when the application layer does not.
  • Faster Router Processing: Compared to IPv4's 20–60 byte variable header, IPv6's fixed 40-byte header enables routers to process packets more quickly.

Disadvantages of IPv6

  • Transition Period: It will take a while to fully switch to IPv6 because IPv4 is still widely used.
  • Communication Barrier: Direct communication between IPv4 and IPv6 machines is not possible.
  • No Backward Compatibility: Because IPv4 systems do not support IPv6, IPv6 cannot operate on computers that support IPv4.
  • Conversion Challenges: The switch from IPv4 to IPv6 is time-consuming due to IPv6's inability to uniquely identify every device on the network.
  • Protocol Isolation: Direct communication between IPv4 and IPv6 is impossible, making cross-protocol communication impossible.

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