So, what you need to know.
An Ipv4 address uses 32 bits.
An Ipv6 address uses 128 bits.
IPv4 addresses are written in dotted decimal.
IPv6 addresses are written using hexadecimal
*Because an hexadecimal number uses 4 bits this means that an IPv6 address consists of 32 hexadecimal numbers. These numbers are grouped in 4’s giving 8 groups or blocks. The groups are written with a ":" as a separator.
Sample IPv4 - 69.89.31.226
Sample IPv6 full - 2001:0db8:0001:0000:0000:0ab9:C0A8:0102
Sample IPv6 short - 2001:db8:1::ab9:C0A8:102
Sample IPv6 short 2 - 2001:db8:1:0:ab9:C0A8:102
In IPv4 an address is split into two components a network component and a node component.
In IPv6 we do the same. The first step is to split the address into two parts. The address is split into 2x64 bit segments the top 64 bits is the network part and the lower 64 bits the node part.
*The upper 64 bits are used for routing. The lower 64 bits identify the address of the interface or node, and is derived from the actual physical or MAC address.
**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 networks, 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.
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(Not Routed internally or externally).
Global addresses are routable on the internet and start with 2001. These addresses are known as global Unicast addresses and are the equivalent of the public addresses of IPv4 networks.
IPv4 internal addresses use the reserved number ranges 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 and 169.254.0.0/16. These addresses are not routed on the Internet and are reserved for internal networks.
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 169.254.0.0/16 which is allocated on an IPv4 network when no DHCP server is found.
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 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16
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.
On IPv4 networks you can access a network rsource e.g. a web page using the format
http://192.168.1.21/webpage
However IPv6 addresses contain a colon as separator and so must be enclosed in square brackets.
http://[IPv6 address]/webpage
The IPv4 loopback address is 127.0. 0.1
The IPv6 loopback address is ::1