Precondition: Multiple DNS server defined.
strict-order
Try each query with each server strictly in the order they appear.
all-servers
Send all queries to all available servers. First reply will be forwarded.
default
Send queries to just one (favoured) server.
Setting all-servers will result in faster responses, but multiplies the number of requests.
Note: The privacy is degraded by setting the wrong servers or setting multiple servers. The flag only changes the mode of service. Reliance on the servers is a prerequisite of using them. Just my 2ct.