[dns-operations] On server selection algorithms in dns resolvers

Mark Andrews marka at isc.org
Mon Nov 23 20:21:26 UTC 2015

In message <93C2F218-FE0A-48A8-92FF-6114FA8E813A at dnss.ec>, Roy Arends writes:
> When resolvers select a server to query, from a pool of many, does the
> pool consist of just addresses, a combination of name-server name and
> address or just name-server names?

This is entirely implementation specific.

> To illustrate, assume a delegation for .example with the following
> records and glue in a fictional root zone.
> example. NS a.example.
> example. NS b.example.
> a.example A
> a.example A
> b.example A
> When the strategy is to select from a pool of addresses or hostnames,
> then there are two in each case, and if the distribution is equal, each
> get 50% of queries.
> When the strategy is to select from a pool of records, then there are
> three (the three A records), and address would get 66% and host
> a.example" would get 66%, etc.

Or it used srtt and it ends up 95% (50% + 45%) and 5%.  With zero knowledge
named initially selects randomly by address.

> Thanks!
> Roy
> PS, Ive read a few papers on server selection algorithms, but none of
> them specify server as name, address or combination.
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org

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