Exploring IPv6 Addressing

Exploring IPv6 Addressing

The IPv6 addressing mechanism uses 128 bits to represent a unique IP address of a network device, unlike 32 bits used by the IPA addressing mechanism. Therefore, a wide range of IP addresses is available to be used in a network. Due to the worldwide availability and connectivity of the Internet, more IP addresses are required to identify devices in the network. As the IPv6 addressing mechanism uses 128 bits, it can serve network purposes properly. The IPv6 address is represented by eight blocks of four hexadecimal digits separated by a colon. Each block of the IPv6 address represents a 16-bit number. The following is an example of the IPv6 address:


The preceding address can also be represented after eliminating leading zeros in the address, as follows:

2001 :db8 : 3c4d :15 : 0 : 0 abcd: ef12

The preceding IP address can also be shortened further by replacing all adjacent zeros blocks by a single set of double colons (only once in the IP address), as follows:


The preceding IP address contains 6 blocks out of the eight blocks; therefore, you can easily determine that the two blocks of adjacent zeros are replaced by double colon (::).

Although, the primary objective of IPv6 addressing is to get a wide range of IP address pool. However, it also provides additional advantages. The advantages of IPv6 addressing include:

  • Routing efficiency: Provides a broad range of IP addresses; therefore, a large number of networks can be assigned with unique IP addresses for routing and communication.
  • Built in Quality of Service: Provides enhanced protection of data packets during transmission and ensures delivery of data packets to the destination network device.
  • Configuration Simplicity: Provides auto configuration of Internet-accessible addresses with or without Dynamic Host Configuration Protocol (DHCP).


Understanding the Structure of IPv6 Addresses

The blocks contained in the IPv6 address represent the network and host components. The number of bits reserved for the network and host components means that the structure of the IPv6 address depends on the IPv6 address type. The three types of IPv6 addresses are as follows:

 Unicast: Recognizes a single interface which consists of a network or subnet and network device. Out of 128 bits of IPv6 address, the primary 64 bits specifies network components (a network or subnet) while other 64 bits specifies host components. The number used to represent network components are determined by IANA and distributed to ISPs. In case of Unicast IPv6 addresses, 64 bits are fixed for network resources, so you need not to define the subnet mask. Rather, it considers the /64 subnet mask by default.

Multicast: Identifies multiple interfaces or network devices in a group. It is similar to the IPv4 broadcast. A data packet sent to the Multicast address is delivered to each interface of a group identified by the Multicast address.

Anycast: Identifies multiple nodes in a network. In case of Anycast IPv6 addressing, a single address is assigned to multiple nodes. When a data packet is sent to Anycast address, it is delivered to the first available node. Consequently, it helps in load-balancing and automatic failover (switching to another standby computer server or network).

After learning about the structure of the IPv6 addresses, now let’s discuss how the computers in the network automatically receive the IPv6 address in the following section.

Receiving IPv6 Addresses on Computers

One of the objectives of upgrading IPv4 addressing to IPv6 addressing is to increase the range of IP addresses. When a computer is connected to a network, it automatically gets a default IPv6 address. However, IPv6 addresses for routers need to be configured manually, as they do not get IPv6 addresses automatically. Although, computers in the network receive IPv6 addresses either from the nearby router or the DHCPv6 server. The automatically assigned IPv6 address can only be used within the subnet. Therefore, you must configure the IPv6 address to computers to communicate with the external network. While configuring the IPv6 address on computers, you come across different types of IPv6 addresses.


Exploring the Types of IPv6 Addresses

The most commonly used IPv6 addresses are IPv6 Unicast addresses that uniquely identify interfaces in a network. IPv6 Unicast addresses are of the following three types:

  • Global addresses
  • Link-local addresses
  • Unique local address


Global Addresses

IPv6 global addresses are globally routable addresses and very similar to IPv4 public addresses. It is also known as the Aggregatable Global Unicast address. The address prefix used for IPv6 global addresses is 2000::/3 that translates a first block value between 2000-3FFF in the hexadecimal notation.

The description of structure of the Ipv6 global address is.

  • 001: identifies the address as the Wv6 global address.
  • Global routing prefix: Identifies a site in a network. The global routing prefixes are handled and distributed to ISPs by IANA.
  • Subnet ID: Identifies a subnet in a network.
  • Host address: Identifies a host in a subnet.



Link-local Addresses

Link-local addresses are used in the subnet for communication among network devices. These addresses are similar to IPv4 APIPA and cannot be used for public IP addresses. Link-local addresses are self-configurable and non-routable.

The description of structure of the 1Pv6 link-local address is:

  • 1111111010 (10 bits) and 00000 .00000 (54 bits): Represents the network address, which cannot be routed.
  • Interface 1D: Identifies a host in a network.
  • Zone ID: Identifies the changes related to each computer in a network with the help of Link-local addresses.


 Unique Local Addresses

IPv6 unique local addresses are meant for local addressing. Unlike link-local addresses, unique local addresses can be used for routing between subnets, but cannot be used for routing from the subnet to the public Internet.

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