The IPv6 address is 128 bits (i.e. 16 bytes) long and is written in 8 groups of 2 bytes in hexadecimal numbers, separated by colons:

  fddd:f00d:cafe:0000:0000:0000:0000:0001

Leading zeros of each block can be omitted, the above address can be written as follows:

  fddd:f00d:cafe:0:0:0:0:1

We can abbreviate whole blocks of zeros with `::` and write:

  fddd:f00d:cafe::1

However, this can only be done once per address to avoid ambiguity:

  ff:0:0:0:1:0:0:1 (correct)
  ff::1:0:0:1 (correct)
  ff::1::1 (ambiguous, wrong)

According to RFC5952 `ff:0:0:0:1::1` is not correct either because the longest group of concurrent zeroes must be shortened.

Static - Fixed Address, SLAAC - Stateless Address Auto-Configuration (Address generated by Host), DHCPv6 - Dynamic Host Configuration Protocol (Address assigned by a central DHCP server).

When working in the world of IPv6, our addresses can vary depending on our scope (i.e. what part of a network): GLOBAL - Everything (i.e. the whole internet), UNIQUE LOCAL - Everything in our LAN (behind the internet gateway), LINK LOCAL - Everything within the same collision domain that will not be routed (i.e. attached to the same switch).

You should always use the smallest possible scope for communication. A host can have multiple addresses in different scopes, even on the same interface.

As in IPv4, IPv6 includes support for network segmentation via Subnetting. In the image below, the first 64 bits are designated as the `Network` portion, while the last 64 bits are for `Host` identification. Within the network portion, the first 48 bits are the `Routing Prefix` - aka the Network Address. The next and final 16 bits of the network notion is the `Subnet ID` or subnet address.

Network+Subnet = Prefix

The following address:

`2003:1000:1000:1600:1234::1` formatted fully as `2003:1000:1000:1600:1234:0000:0000:0001`, consists of the following segments:

- `2003:1000:1000:1600` - Prefix (Combined of Routing Prefix and Subnet ID) - `2003:1000:1000` - Routing Prefix / Network Address - `1600` - Subnet ID / Subnet

If my ISP delegated part of the prefix to me (e.g. `2003:1000:1000:1600/56`), then I could use the subnets `1600` to `16FF` for my own purposes (giving me 256 available subnets).

Because IPv6 address notation uses colons to isolate hextets, it is necessary to encase the address in square brackets in URIs. For example `http://[2a00:1450:4001:82a::2004]`. If you wish to specify a port, you can do so as normal using a colon following the closing square bracket: `http://[2a00:1450:4001:82a::2004]:80`.

Communication from one node to another is called Unicast. Communication from one node to many is called Multicast.

The following IPv6 multicast addresses may be used in in the link-local scope:

A full list is maintained by [IANA](https://www.iana.org/assignments/ipv6-multicast-addresses/ipv6-multicast-addresses.xhtml)

You can actually ping these addresses, e.g. `ping ff02::1`

ICMP does not use ports in order to communicate, but rather types. Critical/important types have numbers ranging from 1-127, while informational types have the numbers 128 and above. Each type can have subtypes or rather codes that can be used for further specifications.

Here are some frequently used IPv6 ICMP types:

A full list is maintained by [IANA](https://www.iana.org/assignments/icmpv6-parameters/icmpv6-parameters.xhtml)

IPv6 addresses can be distributed using the IPv6 version of the Dynamic Host Configuration Protocol (DHCPv6). If a host wishes to obtain an IPv6 address via DHCPv6, it sends out a DHCP Solicitation from UDP port 546 to port 547 on the DHCP multicast address `ff02::1:2`. The DHCP server then replies to the client (from UDP port 547 to UDP port 546) with DHCP Advertisement. This handshake can be completed by the client sending out a DHCP Request and the server responding with a DHCP Reply

The DHCPv6 protocol is explained in more detail in this [Wikipedia Article](https://en.wikipedia.org/wiki/DHCPv6)

Depending on how the router and client are configured, the client can (and will) use both mechanisms (i.e. SLAAC and DHCP) to obtain IPv6 address allocations. The possible configuration combinations are shown in the following table:

To get a better understanding of IPv6 functionality, you can use the packet sniffing tool WireShark to trace the message flow. Here are some WS filters for IPv6 ICMP, DHCPv6 and Router Solicitation and Advertisements:

Show ping and ping reply: `icmpv6 and (icmpv6.type==128) or (icmpv6.type==129)`

Router solicit and advertise: `icmpv6 and (icmpv6.type==133) or (icmpv6.type==134)`

Show DHCPv6 traffic: `dhcpv6`

Router Solicit/Advertise and DHCPv6: `dhcpv6 or (icmpv6 and (icmpv6.type==134) or (icmpv6.type==133))`

Within IPv6, there are a number of message options. All of these message types have a single host transmitting the message and all delivery is handled by the switch or router:

- Unicast is a message sent from one host to one recipient (one to one), - Broadcast is a message sent from one host to all other hosts in the same broadcast domain (One to All), - Multicast is a message sent from a host to all members of a multicast group (One to Specific), - Anycast** is a message sent by a host to the fastest / nearest subscriber of a specific address (One to Specific - Fastest Receiver / Nearest Node will receive).