I think a whole lot of the issue has to do with the supposedly mandatory nature of the
M flag, which leads to phrases like "do DHCP, and only if it fails do auto-config." It
would be much simpler to simply define the flags as "announcing an available service",
as in:
1) The "M" flag is set to indicate that a DHCPv6 address configuration service is
available on this link, as specified in RFC3315.
2) The "O" flag is set to indicate that a DHCPv6 information service is available on
this link, as specified in RFC3736.
We should then leave it at that, and leave it to nodes to decide whether they want to
use these services or not. For example, a server with a configured address will never
use DHCPv6 address configuration; an appliance that never has to resolve DNS names
will never use the information service. By setting the flags to indicate service
availability, we will reduce the amount of useless chatter on the link when the
services are not in fact available.
We should note that, from a protocol point of view, there is no need to use the M bit
to control stateless address configuration. This function is already achieved by the
"Autonomous flag" in the prefix information option. If the flag is not set, the hosts
will not configure information from the prefix.
-- Christian Huitema
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