BIND 10 #859: Search cache for lowest reachable delegation

[BIND 10 Development]

#859: Search cache for lowest reachable delegation
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                   Reporter:         |                 Owner:  UnAssigned
  vorner                             |                Status:  reviewing
                       Type:         |             Milestone:
  defect                             |  Sprint-20110503
                   Priority:  major  |            Resolution:
                  Component:         |             Sensitive:  0
  Unclassified                       |           Sub-Project:  DNS
                   Keywords:         |  Estimated Difficulty:  0.0
            Defect Severity:  N/A    |           Total Hours:  0
Feature Depending on Ticket:         |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Changes (by vorner):

 * owner:  vorner => UnAssigned
 * status:  new => reviewing


Comment:

 Hello

 The code is ready. It took me some time to think it over, but it turned
 out to be quite simple in the end.

 I decided I don't want to take the lowest NS in cache unconditionally.
 Because if I did, the A/AAAA records for it might have expired. The NSAS
 would get the NS from cache, asked for IP addresses, which would generate
 query to the same zone, and we would get a loop. So I check that the NS
 has some address, if not, I move up to the next known delegation. This
 should not increase the number of queries, because we should get the
 A/AAAA with the delegation as glue anyway.

 Unluckily, I can't test it in reality, administrator of my network blocks
 port 53 except his own nameserver. So, if someone could have a look if
 this works and if it solves #833? (It should, in theory, I counted that we
 could have quadratic number of queries in the number of delegations
 before).

 I propose this changelog entry:
 {{{
 [func]          vorner
 We use cache to find lowest usable delegation point, reducing number of
 sent queries.
 }}}

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Ticket URL: <http://bind10.isc.org/ticket/859#comment:1>
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