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IPv6 Network Administration by David Malone, Niall Richard Murphy

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Address Selection

At this stage, it's clear the typical IPv6 node can, and very probably will, have many addresses. Some may be manually configured, others may be automatically configured via router announcements; some may be link-local and others may be global; some may be permanent and others temporary. From this plethora of addresses, a node must make a choice of which address to use. Depending on the criteria used, the choice could change many times over the course of the uptime of a host. In some cases addresses will be explicitly chosen by users or applications, say where a user types telnet ::1, or where a server is bound to a single IP address. For other situations, there needs to be some predictable mechanism for guiding the selection of addresses by a host; these are the default address selection rules, dealt with in RFC 3484.

In any given two-ended communication, there are obviously two addresses that would potentially have to be decided on; the source, and the destination. Source address selection determines which of a node's addresses will be used to originate a connection to a given destination address. Destination address selection would be typically applied to a list of addresses returned by DNS, sorting them in order of preference.

The selection process is given in terms of a sequence of rules that compare two addresses. You start with rule 1, and if it doesn't tell you which address to prefer then you move on to rule 2, and so on. The rules for source address selection ...

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