Hello Daniel
When IPv4 was originally created, each interface, and each host, could only have a single IP address. Later improvements allowed for secondary addresses to be used, which were very useful. For this reason, IPv6 was designed from the beginning to be able to incorporate multiple address assignments.
There are many advantages to being able to so easily assign multiple addresses to an interface. Some of these include:
- The introduction of multiple connections to the Internet with multiple IPv6 routers on the local subnet allows for redundant connectivity without the need for any configuration. Each router will offer a different IPv6 address and default gateway to the host interface. The host can choose which default gateway to use. This offers redundancy as well as simple migration whenever you replace routers on the network.
- Multiple IPv6 addresses also make it very easy to migrate from one IPv6 addressing scheme to another with zero downtime.
- You can also assign multiple IPv6 addresses to a host and have each address associated with a particular application. Some extreme examples of this include experimentation with assigning an IP address to particular content. You can find out more about this at this post.
These are just some of the advantages, and there are of course a lot more… IPv6 moves away from the stricter infrastructure of IPv4 where we have one address, one gateway, manual or DHCP configuration etc… IPv6 becomes more fluid and automated, and part of that is allowing multiple global unicast addresses to be assigned to a single host/interface.
I hope this has been helpful!
Laz