| I’ve been getting a lot of emails asking the | | | | 11111111. A IPv6 multicast address, also has |
| following question; What are IPv6 Unicast, | | | | a 4 bit Flag field which is used to inform if the |
| Multicast, and Anycast addresses? | | | | multicast address is a well-known address (which |
| IPv6 Unicast Addresses are used for one-to-one | | | | is a multicast address that was given to you by |
| communication; currently there are 3 types of | | | | your ISP) or a not well-known multicast address |
| Unicast addresses; Global, Unique-local, and | | | | (which is multicast address that was locally |
| Link-Local. | | | | generated). If the multicast address is a |
| Global Unicast Addresses or GUA’s are | | | | well-known address then the value of all four bits |
| used by devices for one-to-one communication | | | | in the Flag field will be equal to zero. A IP6 |
| across the IPv6 Internet; and every GUA belongs | | | | multicast address, also has a 4 bit Scope field, |
| to a defined Global Scope. GUA’s are easy | | | | which is used to tell the type of Scope that a |
| to identify because their values are always 2000 | | | | IPv6 mulicast address belongs to. A IPv6 multicast |
| or higher; meaning the first three high order bits | | | | address can belong to either one of the following |
| of every GUA that is created, equals 001 | | | | Scopes: |
| or 2000::/3. A GUA is made up of three parts; the | | | | Decimal value Binary Value Address Scope |
| Global Routing Prefix, the Subnet Identifier, and | | | | 1 0001 Interface / Node-local Scope |
| the Interface Identifier. | | | | 2 0010 Link local Scope |
| Unique-Local Addresses or ULA’s are used | | | | 3 0011 Subnet-local Scope |
| by devices for one-to-one communication within | | | | 4 0100 Admin-local Scope |
| an organization (site); and all ULA’s that are | | | | 5 0101 Site-local Scope |
| used within an organization (site) belongs to the | | | | 8 1000 Organization-local Scope |
| same Unique-Local Scope. ULA’s are easily | | | | E 1110 Global-local Scope |
| identifiable because the value of a ULA begins | | | | IPv6 multicast addresses are better to use than |
| with FD00::/8, which simply means that the first | | | | IPv4 multicast addresses, because the address |
| eight high order bits of every ULA address are | | | | range for IPv6 multicasting is much bigger than |
| equal to 11111101. A ULA is made up of | | | | IPv4’s Class D range. |
| three parts; the Global Identifier, Subnet Identifier, | | | | IPv6 Anycast addresses are used for |
| and the Interface Identifier. | | | | one-to-nearest communication, meaning an |
| Link-Local Addresses are used by devices for | | | | Anycast address is used by a device to send |
| one-to-one communication within a layer 2 | | | | data to one specific recipient (interface) that is |
| domain, in other words, link-local addresses are | | | | the closest out of a group of recipients |
| used by devices for one-to-one communication | | | | (interfaces). You would normally want to use |
| within a router’s boundary (the local link). | | | | Anycast addresses for Load Balancing. Think |
| Link-Local Addresses are easily identifiable | | | | about it for a minute. Let’s say you need |
| because the value of a link-local address begins | | | | to send a user’s request to one of many |
| with FE80::/10, which simply means that the first | | | | devices (interfaces); and you don’t really |
| 10 high order bits of every link-local address are | | | | care which of the designated devices handles the |
| equal to 1111111010 and the remaining 54 | | | | request, as long as the request is taken care of. |
| high order bits are equal to zero. Now, just in | | | | By using Anycast addresses, each request is |
| case you were wondering, the 64 lower bits of a | | | | automatically sent to the device (interface) that is |
| link-local address are used for the Interface | | | | in the closest geographic proximity to the |
| Identifier. | | | | computer that is making the request. In certain |
| IPv6 Multicast addresses are used for | | | | other situations, Anycast addresses can even be |
| one-to-many communication; meaning a multicast | | | | used to provide fault tolerance should a router fail. |
| address, identifies a group of network interfaces | | | | The failure can be detected, and requests can be |
| (devices) and when a packet of data is sent to a | | | | redirected to the next closest router. Currently, |
| multicast address, that packet is sent to all of the | | | | IPv6 Anycast addresses have no special |
| network interfaces (devices) that are in the | | | | addressing scheme; they are considered to be |
| multicast group. | | | | structurally indistinguishable from unicast |
| Multicast addresses are easily identifiable because | | | | addresses, so that means nodes have to be |
| the value of a IPv6 multicast address begins with | | | | configured to understand that the unicast address |
| FF (FF00::/8), which simply means that the | | | | that has been assigned to their interfaces is an |
| first 8 high order bits are equal to one or | | | | Anycast address. |