Hemant Singh (shemant) wrote:
An RS with a unicast destination is legal as per RFC 4861. For example,
first time when a host was initialized, the host sent an RS with mcast
destination. Then the host received an RA and the host acquired IPv6
address(es) and is up and running. After a while the host detaches from
the link and reattaches, or the host network interface is disabled by
admin and enabled again. In such cases, the host does know the unicast
destination of the default router. So the next time the host is enabled
or reattached, the host can unicast the RS directly to the router.
How can the host know that it hasn't been reattached to a different
network during this outage? (Well ... the unicast RS should reveal that
of course, but a multicast RS would do the same job too.)
If the subnet has several routers present and the host only cares about
one of them (for whatever reasons, security, configuration, ...) I think
that might be a good reason to use unicast RS. Or if a mobile host tries
to identify the network by its occupants.
--
Aleksi Suhonen
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