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

Roy Arends roy at dnss.ec
Mon Nov 23 17:09:56 UTC 2015

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?

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.



PS, I’ve read a few papers on server selection algorithms, but none of them specify ‘server’ as name, address or combination.

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