dns.sweep.pattern

This configuration parameter specifies a comma separated list to use when scanning for live DNS servers. For each item in the list, specify the type of scan (t for TCP; u for UDP) and the number of seconds to wait for a response.

For example, the following pattern:

dns.sweep.pattern: t1, u1,u2

specifies:

  • A TCP scan with a one second wait for a response
  • A UDP scan with a one second wait for a response
  • Another UDP scan with a two second wait for a response

For each value, all known DNS servers are queried. If the kset.dns.server file exists, the server it defines is queried first.

For initial DNS server acquisition, the first DNS server to respond is chosen, at which point the sweep is terminated. Since the kset.dns.server file is queried first, the server it defines is most likely to be selected. Otherwise, the first server specified in /etc/resolv.conf responds first

For background DNS sweeps, the entire sweep pattern is completed, at which point the fastest server to respond is chosen and the sweep is terminated.

If a new DNS server is selected, the kset.dns.server file is updated with its address.

If the end of the list is reached and no DNS servers respond, DNS is considered down. A new sweep begins after the period of time specified by the dns.dead.resweep.interval.

The default pattern for Linux and Unix is:

dns.sweep.pattern: t1,u1,u1,t2,u2,u2

The default pattern for OS X is:

dns.sweep.pattern: u1,u1