Thursday, February 16, 2017

Zero, One, or Infinity

An interesting tidbit from a NANOG/DNS post:
"But needing “multiple” DNS Root Zone Servers and coming up with the number 13 appears to be somewhat curious. It seems such an odd limitation in the number of root servers given that a common rule of thumb in computer software design is Willem van der Poel’s Zero, One or Infinity Rule, which states a principle that either an action or resource should not be permitted (zero), should happen uniquely (one) or have no arbitrary limit at all (infinity). For root servers, it appears that we would like more than one root server. But why set that number to 13?"
Leading to:
"The desire in the design of the DNS priming query and response was to provide the longest possible list of root name servers and addresses in the priming response, but at the same time ensure that the response was capable of being passed in the DNS using UDP. The largest possible set of names that could be packed in a 512 octet DNS response in this manner was 13 such names and their IPv4 addresses - so there are at most 13 distinct root name servers to comply with this limit." 

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