BIND 10 #3246: Fix problem with PD hints collisions

[BIND 10 Development]

#3246: Fix problem with PD hints collisions
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                   Reporter:  tomek   |                 Owner:
                       Type:  defect  |                Status:  new
                   Priority:  high    |             Milestone:  New Tasks
                  Component:  dhcp6   |              Keywords:
               CVSS Scoring:          |             Sensitive:  0
            Defect Severity:  Low     |           Sub-Project:  DHCP
Feature Depending on Ticket:          |  Estimated Difficulty:  0
        Add Hours to Ticket:  0       |           Total Hours:  0
                  Internal?:  0       |
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 Client's PD hint will be accepted without any processing (only checked if
 it is not used and belongs to valid scope), even if the host part of the
 prefix (e.g. least significant 9 bytes, when sending /56 prefix) has non-
 zero values. This allows collision of two prefixes that are essentially
 the same (e.g. 2001:db8::1/64 and 2001:db8::2/64) to be assigned.

 This is easy to fix. The server must zero the last 128-prefix_len bits
 before processing hint.

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Ticket URL: <http://bind10.isc.org/ticket/3246>
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BIND 10 Development