Query order in db.cache

[Johan Larsson (EAB)]

Hi!

I have a question regarding how the DNS servers listed in the file db.cache are queried. 
IN "DNS & BIND" 3 ed. page 390-391 there is an example of the db.cache file with internal root name servers. It says:

"If the internal name server doesn't have any "better" information cached, it starts by querying an internal root name server. If it has communicated with the internal roots before, it has a round-trip time associated with each, which tells it which of the internal roots is responding to it most quickly."

Fine with that, but I need to know more about how this query algorithm works. If it has not communicated with the internal roots before, which one will be contacted first? If this one is down, how long will it wait until the next one is contacted? etc. 
If anyone is familiar with how this works I would be glad to hear about it.

Thanks,
Johan