IPv6 Address Basics.

By | November 17, 2022

In IPv4 an address is split into two portions a network portion and a host portion.This was done initially using Address classes and later using subnet masking.

In IPv6 we also have the same. The first step is to split the address into two parts.

The address is split into 2 64 bit segments the first 64 bits is the network part and the second portion 64 bits is the host part:

The first 64 bits are used for routing.

The last 64 bits identify the address of the interface or node and is derived from the actual physical or MAC address using IEEE’s Extended Unique Identifier (EUI-64) format. See this Wiki description for exact details.

If we look at the upper 64 bits in more detail we can see that it is split into 2 blocks of 48 and 16 bits respectively the lower 16 bits are used for subnets on an internal network, and are controlled by a network administrator.

The upper 48 bits are used for the global network addresses and are for routing over the internet.

Address Types.

2001:db8::/32Documentation prefix used for examples
fc00::/7Unique Local Addresses (ULA) – also known as “Private” IPv6 addresses.
fe80::/10Link Local addresses, only valid inside a single broadcast domain.
2001::/16Global Unique Addresses (GUA) – Routable IPv6 addresses.
ff00::0/8Multicast addresses
IPv6 Types.

IPv6 addresses have three types:

  • Global Unicast Address –Scope Internet- routed on Internet
  • Unique Local — Scope Internal Network or VPN internally routable, but Not routed on Internet
  • Link Local – Scope network link- Not Routed internally or externally.

Global and Public Addresses

Global addresses are routable on the internet which we called as public IP and start with 2001:

These addresses are known as global Unicast addresses and are the equivalent of the public addresses of IPv4 networks. These addresses are globally unique.

The Internet authorities allocate address blocks to ISPs who in turn allocate them to their customers. read more in  Global Address assignments

Internal Addresses- Link-Local and Unique Local

In IPv4 we have internal or private IP addresses use the reserved number ranges, and and

These addresses are not routed on the Internet and are reserved for internal network usage within the LAN segment.

IPv6 also has two Internal address types.

  • Link-Local
  • Unique Local

Link Local

These are meant to be used inside an internal network, and again they are not routed on the Internet.

It is equivalent to the IPv4 address which is allocated on an IPv4 network when no DHCP server is found. This is the range of APIPA.

Link local addresses start with fe80

They are restricted to a link and are not routed on the Internal network or the Internet.

Link Local addresses are self assigned i.e. they do not require a DHCP server.

A link local address is required on every IP6 interface even if no routing is present.

Unique Local

Unique Local are meant to be used inside an internal network.

They are routed on the Internal network but not routed on the Internet.

They are equivalent to the IPv4 addresses are, and

The address space is divided into two /8 spaces: fc00::/8 for globally assigned addressing, and fd00::/8 for locally assigned addressing.

For manually assignment by an organisation use the fd00 prefix.

Using IPv6 Addresses in URLs

On IPv4 networks you can access a network rsource e.g. a web page using the format

However IPv6 addresses contain a colon as separator and so must be enclosed in square brackets.

http://[IPv6 address]/webpage.

IPv6 Loop Back

The IPv6 loopback address is ::1. You can ping it as follows:

ping ::1 -6

C:\Users\hp>ping ::1 -6

Pinging ::1 with 32 bytes of data:
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms
Reply from ::1: time<1ms

Ping statistics for ::1:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 0ms, Maximum = 0ms, Average = 0ms


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