When does the situation arise where the router advertises more than one prefix to hosts on the link? Is there any use-case scenario for this situation?
One router interface may be configured to advertise more than one prefix, or there may be more than one router on the link both advertising prefixes. This is completely up to the administrator. A situation where you may want to configure more than one prefix on a link could be if you configure a prefix for a global IP address (what you would call a public IP address in the v4 world) and in addition to this use a local IPv6 address (which you would call a private address in the v4 world) for use within the corporate network. In the v6 world, it will be common to have multiple addresses per interface and use the possibilities offered thereby to create new security concepts. You can find all the details about this in Chapter 3 of "IPv6 Essentials."
Hope this helps.
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