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Address Types

Another thing that is different for IPv6 is address types. With IPv4, there were unicast, multicast, and broadcast address types; IPv6 gets rid of the broadcast address type and adds the anycast address type.

There are different sub types within the Unicast address type; these include aggregatable global addresses (or just global address) and link-local addresses. These global addresses are the addresses that are assigned for public routing and work for use in normal network/internetwork tasks. Global IPv6 addresses always start with the first three bits as ‘001’. The link-local addresses are analogous to the 169.254.0.0 IPv4 range, and they are automatically configured for every IPv6 network interface and are used for local network communications. Each of these link-local addresses start with FE80::/10. These addresses are not to be used for public routing.

Multicast with IPv6 has the same one-to-many relationship with hosts as with IPv4. Multicast type addresses with IPv6 always begin with FF::/8. The next four bits are dedicated to flags, and the next four bits after that are dedicated for scope. The scope field is used to configure how far the multicast is intended to go. The following table shows the scope options:

Scope

Purpose

1

Interface-local

2

Link-local

4

Admin-local

5

Site-local

8

Organization-local

E

Global

With IPv6, the broadcast address type has been replaced with the anycast address type. This may just seem like a simple name change, but the behavior of an anycast address is not the same as a broadcast address; with IPv6, there is no facility that allows the behavior of an IPv4 broadcast. Anycast works by selecting a member of the specific anycast address that is closest to the one requesting it. For example, if all the root DNS servers were in an anycast group and your DNS server was searching for the closest one to use, the anycast group would identify this for you and automatically send the traffic to the closest device.

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