Computer Networking

What is IPv6?

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February 19, 2011 5:30AM

What we have used up to now(IPv4) has been used up(32 bit). With new devices adding in to the network we need a bigger address space.

So IPv6 comes with lot of extended capabilities like,

  • Expanded address space
  • Expanded routing capabilities
  • Simplified header format
  • Support for authentication and privacy
  • Quality of service (QoS) capabilities


Time taken by a packet to reach the destination from the source, we call it "Delay". Variation of that delay we call as "Jitter". Jitter is dangerous much more than delay. We have to reduce it to provide QoS

In IPv6 Packet we see no of header fields

Traffic Class - This contain a number which represent the priority level this is what make QoS possible.

Flow Label - Contain a small no which is easy to handle This make routing faster and easy.

In IPv6 we find 128 bit address. There are there kinds of addresses

Uni-cast = A packet with a uni-cast address to a single interface identified by that address. ID for single interface

Any-cast = ID for group of interfaces. But packet will be delivered to the nearest one.

Multi-cast = ID for group of interfaces. Packet will go to everyone identified by that address.


Loop back address( - Virtual address that return to same node.

Addressing model

  • Ipv6 addresses are assigned to interfaces, not nodes.
  • All interfaces must have at least one link-local uni-cast address.(A single interface may have more than one ipv6 address having different type and scope)

Address representation

  • x:x:x:x:x:x:x:x, where 'x' s are the hexadecimal values of the eight 16-bit pieces of the address
  • Can omit leading 0s at each field. But there must be one character in every field.

    e.g. 23A7:00F3:0004:0000…. = 23A7:F3:4:0….

  • :: represent one or more groups of zeros (only once in a address).

    e.g. 23:0:0:0:0:3456:A987:8 = 23::3456:A987:8

  • x:x:x:x:x:x:d.d.d.d, where 'x' represent 16 bit hexadecimal values and 'd' represent 8 bit values

    e.g. A234:0:0:0:0:FFFF:

  • Uses CIDR notation as in IPv4 (ipv6-address/prefix-length )

    E.g. 12AB:0000:0000:CD30:0000:0000:0000:0000/60

    Address type indicated by leading bits

TypeLeading bitsAggregatable Global Uni-cast Addresses001Link-local Uni-cast Addresses1111 1110 10Site-local Uni-cast Addresses1111 1110 11Multicast Addresses1111 1111Reserved0000 0000


Loopback address - ::1

Unspecified address - :: (has no scope, cannot be assigned to any interface)

The format prefixes 001 through 111(001, 011, 101, 111 as there should be 1 at the end), except for Multicast Addresses, are all required to have to have following format.

This IEEE EUI - 64 is generated using MAC

c - company bits, m - device bits, g - global bit

IPv6 addresses with embedded IPv4 addresses

IPv4-compatible IPv6 address

IPv4-mapped IPv6 address

Hierarchical Addressing

  • This situation first ISP was given It distribute this between 8 companies. To represent 8 companies we need 3 bits. new subnet will be 23.

IPv6 with hierarchical Addressing

Transition from IPv4 to IPv6 (rfc 2893)

Two approaches

  • Dual Stack approach

    • IPv6 nodes should also have full implementation of IPv4 stack
    • If any of the two ends is only IPv4 capable then both ends must communicate in IPv4
  • Tunneling approach

    • Encapsulate IPv6 datagram with an IPv4 header