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1.9 Describe IPv6 address types

Global unicast 2000::/3

These are IPv6 addresses that can be obtained from an RIR, and are routable across the internet. They are globally unique and should only be used by the organisation that has registered them. Global unicast addresses are available from the 2000::/3 address block, which allows for a huge number of networks to be provided worldwide. This has now been changed to include all addresses that aren't reserved for other purposes. See at the end of this article for a table to reference IPv6 reservations.

 

Typically organisations are provided with a /48 address block which is known as the Global Routing Prefix. Normally organisations will subnet this down to a /64 block allowing for over 65,000 networks.

Unique local FD00::/7

A unique local address is a private address space. Similar to how 10.0.0.0/8, 172.0.0.0/12 and 192.168.0.0/16 were reserved for private address use in IPv4. These IPv6 addresses cannot be routed over the internet and are solely for use within a LAN. Any unique local addresses do not need to be registered with the RIR. Unique local addresses start with FD00::/7, so wherever you see an IPv6 address beginning with FD, you can easily identify it as a unique local address. The 40 bit global ID should always be randomly generated because if two organisations merge and say both global IDs are all 0s, then it will be a huge task to renumber all of the networks.

Link Local fe80::/10

These addresses are using only for directly connected interfaces and routers will not route packets with link local destination addresses. Link local addresses are used by NDP (Network Discovery Protocol) and as a next hop address. These addresses use the address block fe80::/10. Note that the 54 bits after fe8 are set to 0, so the remaining 64 bits are unique. For example:

Devices typically either auto-generate their link local addresses via EUI 64 methodology, or via randomisation. We'll go into EUI 64 in more depth later on in this article. The zone identifier is for the device only and requires no manual configuration. It simply identifies the interface that the link local address is bound to. On a PC you may have multiple interfaces so you'll see this zone identifier appended to the end of the address.

 

Anycast

Anycast is a newer feature of IPv6, and allows for one to one of many communication. There is no defined address block for anycast addresses but will use a unique global or unique local address. When IPv6 addresses are configured on a Cisco router, add the word "anycast" to the IPv6 address being added to the interface. Such as:

 

nbRTR1(config)#intGi0/1

nbRTR1(config-if)#ipv6 address 2001:db80::5612/64 anycast

 

Routers will forward the packets to the closest router based on routing metrics.

 

Multicast

Multicast is used by IPv6 instead of broadcast which is used in IPv4. The address block for multicast addresses is FF00::/8. Multicast allows traffic to be forwarded to a number of devices (one to many) if they have joined the multicast group. Some key multicast groups to know are below:

IPv6 also defines multicast scopes. These scopes determine how far a multicast packet should be forwarded. Some scopes require additional configuration to put multicast boundaries in place. Below are the relevant scopes that you need to be aware of:

Modified EUI 64

The modified EUI 64 address is method of creating the IPv6 address from the network prefix and the device's 48 bit MAC address. The process for creating the modified EUI 64 address is done automatically on the router, however we need to understand what is happening behind the scenes to generate the IPv6 address. Note that most modern operating systems do not use modified EUI 64 due to security and privacy concerns. The steps to create modified EUI 64 address are as below:

 

  1. Split the MAC address into two

  2. Insert FFFE in between the two halves

  3. Invert the 7th bit and add colons

  4. Add the network prefix to the start of the interface identifier and format for IPv6

Why do we invert the 7th bit? This is because the 7th bit of a MAC address is called the U/L (Universal/Local) identifier. When the bit is set to 0, it is a UAA (Universally Administered Address), meaning the MAC address was assigned by the manufacturer. If it is set to 1, it means that the MAC address is an LAA (Locally Administered Address) which indicates that the MAC address was manually assigned by an engineer.

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