How do nameservers do failover? What decides the order in which nameservers are queried when the primary nameserver is not reachable?
To illustrate, here's part of my zonefile:
$TTL 3m; site.com. IN SOA ns1.sitese.com. admin.site.com. ( 2007010403 ; Serial 1800 ; Refresh [1h=3600] 1800=30m 600 ; Retry [10m] 86400 ; Expire [2weeks] 86400=1day 180 ) ; Negative Cache TTL [1h] ; site.com. IN NS ns1.sitese.com. site.com. IN NS ns2.sitese.com. site.com. IN NS ns3.sitese.com. ns1.sitese.com. IN A 220.127.116.11 ns2.sitese.com. IN A 18.104.22.168 ns3.sitese.com. IN A 22.214.171.124
Obviously the primary nameserver is ns1.sitese.com as it is listed in the SOA record. But which one becomes the secondary nameserver if the primary is unreachable? Is it ns2, or ns3? What decides the order in which secondary nameservers are queried? Is it the order in which they appear in the zonefile? Is it something else?