Re: DNS question

[Matthew Boeckman <matthewb saepio com>]

You labor under a common misconception about primary and secondary DNS. 
Primary and secondary nameservers do not "take over" or "fail over" when 
 one of the pair is down. To the best of my understanding (list 
clarification?), queries to your authoritative servers are doled out by 
the root servers, and are balanced across however many authoritative 
servers you have registered. If a query to one of your authoritative 
servers dies, it can be re-tried against another, and another, etc until 
all authoritative servers have been queried. If you look closely, you 
will see queries going to your secondary all the time, even tho your 
primary is up. The words primary and secondary are confusing, but what 
they really mean is that the secondary (or slave) server gets it's zone 
files from the primary. If the primary dies, it doesn't tell the 
secondary it's gone. The secondary can and will poll the primary for 
updates at whatever interval you define.

Example:

	Let's say you have bob.com, and your nameservers registered with INTERNIC 
are ns1.jane.com and ns2.jane.com. Theoretically, 50% of queries for 
www.bob.com go to ns1, the other 50% go to ns2. In practice, I've never 
seen it split exactly, but more like 70/30. If a query to ns1.jane.com 
times out, (depending on configuration) the _client_ may make a 2nd 
query to ns2 and check it.

I hope that helps, and anyone who is better versed in DNS please feel 
free to correct me. I would highly recommend DNS and BIND from O'Reilly.

matthew

Jim Bija wrote:

> If my primary DNS server goes down (daemon only, the machine and IP etc 
> is fine) will the secondary take over?
>
> It seems some of my machines lag unless the primary DNS server is down, 
> as in the IP is dead.
>
> I seem to have some situations where the secondary seems not to take 
> over. I have heard that M$ machines do not act like linux boxes and have 
> a long timeout period before going to secondary DNS servers. Im asking a 
> general DNS question here as to what are the rules (RFC's) of DNS. Im 
> interested in what is propper, not what M$ does with their products. 
> That i can easily find out on my own. Thanks.
>
>  
>
> Jim.
>
>  


--
Matthew Boeckman			(816) 777-2160
Manager - Systems Integration		Saepio Technologies
== 
						==
/earth is 98% full ... please delete anyone you can.