IPv6 Addressing and Prefix - CSU359 - Shoolini University

IPv6 Addressing and Prefix

2024, August 27

1. IPv6 Addressing

IPv6 (Internet Protocol version 6) is the most recent version of the Internet Protocol (IP), which is designed to address the limitations of IPv4, including the depletion of available IP addresses. IPv6 uses 128-bit addresses, significantly expanding the address space compared to the 32-bit addresses used in IPv4. This allows for a virtually limitless number of unique IP addresses.

IPv6 Address Format

An IPv6 address consists of 128 bits, typically represented as eight groups of four hexadecimal digits, separated by colons. For example:

2001:0db8:85a3:0000:0000:8a2e:0370:7334

  • Hexadecimal Notation: Each group of four digits is a hexadecimal representation of 16 bits.
  • Colon-Separated: Colons (:) are used to separate each group of four hexadecimal digits.
  • Address Simplification: Leading zeros within a group can be omitted, and consecutive groups of zeros can be replaced by a double colon (::), but this can only be done once in an address.
Example:
Original: 2001:0db8:0000:0000:0000:0000:0000:0001
Simplified: 2001:db8::1

1.1 IPv6 Address Types

IPv6, the successor to IPv4, introduces a significantly larger address space and different types of IP addresses. Understanding the various types of IPv6 addresses is crucial for network configuration and management. The primary types of IPv6 addresses include Unicast, Multicast, and Anycast. In this documentation, we will focus on the Unicast address, which is used to identify a single interface within the scope of the address.

1.1.1. Unicast Address

A Unicast address in IPv6 is used to uniquely identify a single interface on a network. Packets sent to a Unicast address are delivered to the specified interface. Unicast addresses can be further divided into three main types:

  • Global Unicast
  • Unique Local
  • Link-Local

1.1.1.1 Global Unicast Address

A Global Unicast address is globally unique and routable on the IPv6 Internet. It is the equivalent of the public IPv4 address. The structure of a Global Unicast address is as follows:

  • Prefix: The first 48 bits of the address, representing the network prefix, assigned by the Internet Assigned Numbers Authority (IANA).
  • Subnet ID: The next 16 bits used to identify a subnet within the network.
  • Interface ID: The last 64 bits, typically derived from the MAC address of the device's network interface, uniquely identifying the interface within the subnet.

Global Unicast addresses are used for communication across the global Internet and are routable. An example of a Global Unicast address format is 2001:0db8:85a3:0000:0000:8a2e:0370:7334.

1.1.1.2 Unique Local Address (ULA)

Unique Local Addresses are similar to private IP addresses in IPv4. They are intended for local communications within a site or organization and are not routable on the global IPv6 Internet. The structure of a ULA is:

  • Prefix: The first 7 bits are always 1111110 (fc00::/7).
  • L (Local): The 8th bit is set to 1 to indicate the address is locally assigned (fd00::/8).
  • Global ID: The next 40 bits are randomly generated, ensuring the address is unique across the site.
  • Subnet ID: The next 16 bits, used for subnetting within the local network.
  • Interface ID: The final 64 bits identify the specific interface within the subnet.

ULAs are used for internal communication within an organization and should not be used for devices that need global connectivity. An example of a ULA format is fd12:3456:789a:1::1.

1.1.1.3 Link-Local Address

Link-Local addresses are automatically configured on all IPv6-enabled interfaces and are used for communication within a single link (i.e., no routers are required). These addresses are not routable beyond the local link. The structure of a Link-Local address is:

  • Prefix: The first 10 bits are always 1111111010 (fe80::/10).
  • Zeros: The next 54 bits are set to zero.
  • Interface ID: The final 64 bits uniquely identify the interface, usually derived from the MAC address.

Link-Local addresses are used for communication between nodes on the same link, such as neighbor discovery and address autoconfiguration. An example of a Link-Local address format is fe80::1ff:fe23:4567:890a.

1.2. Anycast Address

An Anycast address is an IPv6 address assigned to multiple interfaces (typically on different nodes). Packets sent to an Anycast address are delivered to the nearest interface (in terms of routing distance) that holds the address. This type of address is used to route traffic efficiently by directing it to the closest available resource, such as the nearest server in a content delivery network.

1.2.1 Characteristics of Anycast Addresses
  • Shared Address: Multiple devices share the same Anycast address, but only one (the closest in terms of routing) will receive the packets.
  • Routing Efficiency: Anycast improves routing efficiency by reducing latency, as data is delivered to the nearest server or device holding the address.
  • No Special Format: Anycast addresses do not have a special format; they are typically assigned from the pool of Global Unicast addresses.
  • Used for Specific Services: Anycast is often used for services like DNS, where the nearest server should handle the request to reduce response time.
1.2.2 Example Use Case

A common example of Anycast usage is in DNS services. Multiple DNS servers around the world can be assigned the same Anycast address. When a DNS query is made, the request is routed to the nearest DNS server, improving response time and reliability.

Example: DNS Anycast address for Google's Public DNS - 2001:4860:4860::8888

In this example, regardless of where the request is made from, it will be directed to the closest Google Public DNS server configured with that Anycast address.

1.3. Multicast Address

A Multicast address in IPv6 is used to deliver packets to multiple interfaces that are part of a multicast group. Unlike Unicast, where packets are delivered to a single interface, and Anycast, where packets are delivered to the nearest interface, Multicast allows a single packet to be delivered to multiple destinations simultaneously. This is especially useful in applications such as streaming media, online gaming, or real-time data distribution.

1.3.1 Characteristics of Multicast Addresses
  • One-to-Many Communication: Multicast enables one-to-many communication, where a single source sends data to multiple recipients in a group.
  • Efficient Data Distribution: By sending a single packet that is replicated across the network, Multicast conserves bandwidth and reduces the load on the source.
  • Scoped Addressing: Multicast addresses can have different scopes, such as link-local, site-local, or global, determining how far the multicast traffic can travel.
1.3.2 IPv6 Multicast Address Format

IPv6 Multicast addresses begin with the prefix ff00::/8. The structure of an IPv6 Multicast address is as follows:

  • Prefix: The first 8 bits are always 11111111 (ff00::/8), indicating a Multicast address.
  • Flags: The next 4 bits are reserved for flags that provide additional information about the multicast group (e.g., whether it's permanently assigned).
  • Scope: The next 4 bits define the scope of the multicast group (e.g., 1 for interface-local, 2 for link-local, 5 for site-local, etc.).
  • Group ID: The last 112 bits identify the specific multicast group.

Example of a Multicast address format: ff02::1 (All nodes on the local link).

1.3.3 Common IPv6 Multicast Addresses
  • ff02::1: All nodes on the local link. This address is used for Neighbor Discovery and other link-local communications.
  • ff02::2: All routers on the local link. This is used for router discovery and routing protocol communications.
  • ff05::1:3: All DHCP servers on the site-local network. This is used for DHCP communication within a site.
1.3.4 Example Use Case

Multicast is widely used in IPTV (Internet Protocol Television), where a single stream of video content can be distributed to multiple subscribers simultaneously. When a user subscribes to a channel, their device joins the corresponding multicast group, and the video stream is delivered efficiently to all subscribers in that group.

Example: IPTV uses Multicast to stream video content to multiple subscribers without sending separate streams to each user.

1.4. Modified EUI-64

The Modified EUI-64 format is a method used in IPv6 to automatically generate the Interface ID portion of an IPv6 address from a device's MAC address. This process ensures that the Interface ID is unique within a given network, and it is particularly useful for Stateless Address Autoconfiguration (SLAAC), where devices generate their own IPv6 addresses without the need for a DHCP server.

1.4.1 Structure of the Modified EUI-64 Address

The Modified EUI-64 format creates a 64-bit Interface ID from a 48-bit MAC address by following these steps:

  • Step 1: Split the MAC Address: The 48-bit MAC address is split into two 24-bit halves.
  • Step 2: Insert the "FFFE" Segment: The 16-bit segment FFFE is inserted between the two halves, creating a 64-bit value.
  • Step 3: Invert the Universal/Local (U/L) Bit: The 7th bit of the first byte (the U/L bit) is inverted. If it was a 0 (indicating a globally unique MAC address), it is changed to 1 (indicating a locally administered address), and vice versa.

An example conversion of a MAC address to an IPv6 Interface ID:


            Original MAC Address: 00-1A-2B-3C-4D-5E
            Step 1: Split into two halves: 00-1A-2B and 3C-4D-5E
            Step 2: Insert FFFE: 00-1A-2B-FF-FE-3C-4D-5E
            Step 3: Invert the U/L bit: 02-1A-2B-FF-FE-3C-4D-5E

The resulting Interface ID is 021A:2BFF:FE3C:4D5E.

1.4.2 Usage in IPv6 Addressing

The Modified EUI-64 format is primarily used in Stateless Address Autoconfiguration (SLAAC). In this context, the Interface ID generated through the Modified EUI-64 process is combined with a network prefix (typically 64 bits) to form a complete IPv6 address.

For example, if the network prefix is 2001:0db8:85a3::/64 and the Interface ID is 021A:2BFF:FE3C:4D5E, the resulting IPv6 address would be 2001:0db8:85a3:021A:2BFF:FE3C:4D5E.

1.4.3 Advantages and Considerations
  • Unique Addressing: The Modified EUI-64 method provides a straightforward way to generate unique Interface IDs, ensuring no two devices on the same network have the same IPv6 address.
  • Privacy Concerns: The use of MAC addresses in generating the Interface ID can lead to privacy concerns, as it can be used to track devices across different networks. To address this, Privacy Extensions for IPv6 have been introduced to generate random Interface IDs.
  • Autoconfiguration: This method simplifies network configuration by allowing devices to self-configure their IPv6 addresses without the need for a DHCP server.

1.5. IPv6 Address Scopes

IPv6 addresses have specific scopes that define where they are valid:

1.6. IPv6 Address Configuration Methods

IPv6 allows for both manual and automatic address configuration:

1.6.1 Stateless Address Autoconfiguration (SLAAC)

In SLAAC, devices generate their own IP addresses using the prefix provided by a router and the device's MAC address. This method does not require a DHCP server.

1.6.2 DHCPv6

Similar to DHCP in IPv4, DHCPv6 assigns IPv6 addresses to devices on a network, along with other configuration information. It can be stateful (maintaining a record of allocated addresses) or stateless (providing only configuration information without tracking address allocations).

1.6.3 Manual Configuration

Administrators can manually assign IPv6 addresses to devices. This is typically used in situations where specific, fixed addresses are needed.

1.7. IPv6 Addressing Benefits

IPv6 addressing offers several key benefits over IPv4:

1.8. IPv6 Address Representation in Binary

Each hexadecimal digit in an IPv6 address represents 4 bits of the 128-bit address. To understand IPv6 at a low level, it is important to recognize how these hexadecimal digits translate to binary.

Example:
IPv6 Address: 2001:db8::1
Binary Representation: 
0010 0000 0000 0001 : 0000 1101 1011 1000 : 0000 0000 0000 0000 : 0000 0000 0000 0001

2. IPv6 Prefix

An IPv6 prefix is a portion of the address that indicates the network portion, similar to the concept of a subnet mask in IPv4. The prefix length is denoted by a slash ("/") followed by a number, which specifies the number of bits that make up the network portion of the address.

2.1 Structure of an IPv6 Prefix

An IPv6 address can be divided into two parts:

  • Network Prefix: The leftmost part of the address, determined by the prefix length. It identifies the network or subnet.
  • Interface Identifier: The rightmost part of the address, determined by the remaining bits. It uniquely identifies an interface within the network.
Example:
IPv6 Address: 2001:0db8:85a3:0000:0000:8a2e:0370:7334/64
Network Prefix: 2001:0db8:85a3::
Prefix Length: /64
Interface Identifier: 0000:0000:8a2e:0370:7334
2.2 Common Prefix Lengths

In IPv6, the prefix length is flexible and can be adjusted depending on the network's size and design. However, some common prefix lengths are:

  • /64: The most common prefix length, typically used for a single subnet. It allows for a vast number of hosts (264 addresses).
  • /48: Commonly used for large organizations, allowing multiple subnets within a site.
  • /32: Often used by ISPs to allocate large blocks of addresses to customers.
  • /128: Refers to a single specific interface. This is used for loopback addresses or specific device assignments.
2.3 IPv6 Global Routing Prefix

The global routing prefix is the part of the address assigned to an organization by an Internet registry or ISP. It is typically the first 48 bits of the address, and it is used to route traffic globally on the Internet.

Example:
IPv6 Address: 2001:0db8:85a3:0000:0000:8a2e:0370:7334/64
Global Routing Prefix: 2001:0db8:85a3::
2.4 Subnetting in IPv6

Subnetting in IPv6 is similar to IPv4 but allows for more granular and scalable networks due to the larger address space. A common practice is to use a /64 prefix for individual subnets, providing ample address space within each subnet.

Example:
Subnet with /64 prefix: 2001:0db8:85a3:0001::/64
Another subnet: 2001:0db8:85a3:0002::/64

3. Configure and Verify IPv6 Addressing and Prefix

Configuring and verifying IPv6 addressing involves assigning an IPv6 address and prefix to a network interface and ensuring it is correctly set up for communication. This process can be done on various operating systems and networking devices. Below are the general steps and commands for configuring and verifying IPv6 addressing.

3.1 Configuring IPv6 Addressing
3.1.1 Linux/Unix Systems

To configure an IPv6 address on a Linux/Unix system, use the ip command:

sudo ip -6 addr add 2001:0db8:85a3::1/64 dev eth0

Here, 2001:0db8:85a3::1/64 is the IPv6 address and prefix, and eth0 is the network interface.

3.1.2 Windows Systems

To configure an IPv6 address on a Windows system, use the netsh command:

netsh interface ipv6 add address "Ethernet" 2001:0db8:85a3::1/64

Here, Ethernet is the name of the network interface, and 2001:0db8:85a3::1/64 is the IPv6 address and prefix.

3.1.3 Cisco Devices

To configure an IPv6 address on a Cisco router or switch, enter the following commands in global configuration mode:

Router(config)# interface GigabitEthernet0/0
Router(config-if)# ipv6 address 2001:0db8:85a3::1/64
Router(config-if)# ipv6 enable

Here, GigabitEthernet0/0 is the interface, and 2001:0db8:85a3::1/64 is the IPv6 address and prefix.

3.2 Verifying IPv6 Addressing
3.2.1 Linux/Unix Systems

To verify the IPv6 address configuration on a Linux/Unix system, use the ip command:

ip -6 addr show dev eth0

This command will display the configured IPv6 address and prefix for the interface eth0.

3.2.2 Windows Systems

To verify the IPv6 address configuration on a Windows system, use the ipconfig command:

ipconfig /all

This command will display all network interfaces and their IPv6 addresses.

3.2.3 Cisco Devices

To verify the IPv6 address configuration on a Cisco device, use the following command in privileged EXEC mode:

Router# show ipv6 interface GigabitEthernet0/0

This command will display the IPv6 address and prefix assigned to the interface GigabitEthernet0/0.

3.3 Testing IPv6 Connectivity

Once the IPv6 address is configured, you can test connectivity using the ping command.

3.3.1 Linux/Unix and Windows Systems

To test IPv6 connectivity, use the following command:

ping6 2001:0db8:85a3::1

or on Windows:

ping -6 2001:0db8:85a3::1

This command sends ICMPv6 echo requests to the specified IPv6 address and verifies whether the device is reachable.

3.3.2 Cisco Devices

To test IPv6 connectivity from a Cisco device, use the following command:

Router# ping ipv6 2001:0db8:85a3::1

This command tests connectivity to the specified IPv6 address.

3.4 Troubleshooting IPv6 Configuration

If connectivity issues arise, consider the following troubleshooting steps:

  • Check Interface Status: Ensure that the network interface is up and running.
  • Verify Prefix Length: Ensure the correct prefix length is configured. Incorrect prefix lengths can lead to routing issues.
  • Check for Duplicate Addresses: Ensure no other devices on the network are using the same IPv6 address.
  • Review Routing Tables: Verify that the routing table includes the correct routes for the IPv6 prefix.
  • Use traceroute6 or tracert -6: These commands can help identify where connectivity breaks down along the path to the destination.