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introduction to IPv6 – part 1

To start using IPv6 in our labs, I decided to prepare a short introduction of it. As it is a broad topic I had to split it into several parts. Let’s start from the beginning.

Short IPv6 history

First IPv6 protocol specification was introduced in late 1995 in RFC1883, so it was 18 years ago! About one year later 6bone network was started as a virtual network over the IPv4-based Internet (using IPv6 over IPv4 tunneling). The mission of the 6bone was to establish the IPv6 environment for testing purposes.  In 1999 IPv6 Forum was founded and registries started assigning IPv6 prefixes to ISPs. In 2000, many vendors began to bundle IPv6 into their mainstream product lines. 2009 – first serious IPv4 address shortage in developed countries.

What about IPv5?

IPv5 was an experimental Resource Reservation Protocol, intended to provide QoS for multimedia and defined as the Internet Stream Protocol version 2 (ST2). It was designed to coexist with IPv4 and use the same addressing scheme, not as a replacement of IPv4. ST2 was designed to coexist with IPv4 on each node. The main role of the ST2 was to transfer a real-time multimedia, where IPv4 could be used for the transfer of traditional data and control information. ST2 is described in RFC1819.

IPv6 benefits

There are several features, that make it attractive, for building global-scale networks:

  • Larger address space. IPv6 address is 128-bit, 4 times larger than IPv4. It allows to address ~3,4*1038 nodes. It gives 340282366920938463463374607431768211456 possible addressable nodes.
  • Global reachability. IPv6 enables to use of a global and reachable address for almost every kind of device, such as computers, IP phones, tablets, PDAs, TVs, vehicles.
  • Autoconfiguration. Enables “plug-and-play”. IPv6 host can autoconfigure itself with a complete 128-bit globally unique address.
  • Simpler header and simpler processing in hardware. Half of the previous IPv4 header fields were removed. All IPv6 header fields are aligned to 64 bits, which allows easier storage and access in memory.
  • End-to-end security. IPsec is mandatory in IPv6, every node will have IPsec enabled.
  • Mobility built in IPv6.

IPv6 address formats

IPv6 addresses are represented as a series of eight 16-bit hexadecimal fields, that are separated by colons:

X:X:X:X:X:X:X:X, where X is a 16-bits hexadecimal field, for example:


Leading zeros in a field are optional. Successive fields of zeros can be represented as a double colon (::), but this can be used only once in an address. Using these techniques, IPv6 addresses can be very small. Our address mentioned above, can be written as:


Other examples of IPv6 addressess:

FF02:0000:0000:0000:0000:0000:0000:0001 can be represented as FF02::1
0000:0000:0000:0000:0000:0000:0000:0000 can be represented as ::

IPv6 address types

There are three main types of addresses supported by IPv6:

  • Unicast
  1. Global unicast
  2. Link-local
  3. Unique local
  4. Special-purpose: Unspecified, Loopback, IPv4-mapped
  • Multicast
  • Anycast

There is no broadcast address, in the way, it is used in IPv4. Its function is superseded by multicast addresses.

IPv6 global unicast address

Global unicast address space corresponds to the principal use of IPv6 addresses, for generic global IPv6 traffic. These addresses can be allocated by registries only from the range of addresses, that start with binary value 001 (2000::/3). The structure of this address is as follows:


  • A global routing prefix assigned to a site, typically /48
  • A subnet identifier, used to identify links within a site, typically 16-bit long
  • A 64-bit interface identifier

Example of a global unicast address:

2013:AB01:0000:0000:DC10:B210:5C13:4512 or simply 2013:AB01::DC10:B210:5C13:4512

For more information about IPv6 global unicast addresses see RFC3587, IPv6 Global Unicast Address Format.

IPv6 link-local address

IPv6 link local address must be assigned to every IPv6 enabled interface. The scope of this address is limited to the link. Link-local addresses are automatically created, using a specific prefix, FE80::/10 and a 64-bit interface identifier. This type of IPv6 address can be used to connect devices on the same link or local network, where global or unique local addressing is not a requirement. Routing protocols use this address type as a next-hop address.


Example of a link-local address:

IPv6 unique local address

Local unicast addresses are defined in RFC4193, Unique Local IPv6 Unicast Addresses. Prefixes start with FC00::/7, where:

  • FC00::/8 is planned to be globally managed
  • FD00::/8 can be assigned locally by administrator (L bit set to 1)


Unique local address space has a local site scope. It can be used by organizations that prefer a concept of private address space for internal communication. Unique local address space can be used independently of any provider-based IPv6 unicast address allocation.

40-bit global ID field is a pseudo-random and must not be assigned sequentially or with well-known numbers. It gives an assurance that any network numbered, using such a prefix, is highly unlikely to have that address space clash with any other network, that has another locally assigned prefix, allocated to it. This is particularly useful in case of network merge, because allows sites to be combined, without creating any address conflicts or renumbering of interfaces.

Special purpose addresses


The loopback address identifies a local interface in the IP stack. It is the IPv6 equivalent of the IPv4 loopback. In IPv6 world the address is 0:0:0:0:0:0:0:1, or simply ::1

Unspecified address

This address is used, when no address is available, for example it can be used as a source address, when a host requests an address to a DHCP server. This address is 0:0:0:0:0:0:0:0, or simply “::”.  It indicates the absence of an address and must not be used as a destination address.

Next time I will try describe multicast and anycast IPv6 addressing concepts.

Do you have any experience in the IPv6 implementation? Would you like to express your opinion? Feel invited to comment.

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