Bind internal behavior when used as resolver

Surya ARBY arbysurya at yahoo.fr
Sat Jul 19 17:13:22 UTC 2008


Hello all.
I'm making a study about GSLB (Global Site Load Balancing) which is some kind of "advanced" load balancing based on DNS. To be exhaustive and to be sure to understand impacts on clients, I need to know how Bind behaves when used as resolver/caching system. In fact I couldn't find any reliable information on the Net, and the official documentation doesn't describe the internal processing of Bind.

Here are my questions, I hope someone will be able to reply :-)


- By default, does Bind honor the TTL value read in DNS answers ?

- Is it possible to overwrite this TTL value to use another one defined by the local administrator ?

- What is the behavior when TTL read is equal to 0 ? Can we be sure it doesn't cache ? Also, if TTL = 0 , can I overwrite this value ?

- Is TTL overwriting often used ?



About Multiple IP Responses, when Bind sends a query for domain name (for example www.foo.com) and the reply contains multiple IP addresses, how does it behaves ? 

I read that Bind sends to the clients only one IP address took in the pool in a pseudo-random (Round Robin ?) fashion. Is it true ?

Also, is Bind configurable to reply with all IP addresses to the client ? In this case, is the initial order of IP addresses received initially by Bind preserved ? If not, I suppose that Multiple IP addresses are rotated in a pseudo-random fashion.


regards,

Surya



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