Bind internal behavior when used as resolver

[Kevin Darcy]

Homework is homework, whether it's for a school assignment, or as 
background research for the development of some "solution" you're going 
to pitch to a customer. Frankly, I think your customer deserves a little 
more due diligence than simply regurgitating some informal, free advice 
you got from some mailing list.

Since you're short on time, and on the off-chance that you (or some 
more-DNS-knowledgeable person at your company) would go through the 
extraordinary ordeal of setting up at least 1 Internet-resolving 
nameserver with BIND, here's how to answer your questions:
a) "does BIND honor TTL?". Query small-ttl.5test.com, wait more than 10 
seconds, then do a non-recursive query for the name and see if it resolves
b) "does BIND cache records with TTL=0"? query zero-ttl.5test.com 
multiple times, which has a TTL of 0. Turn up your logging sufficiently 
to see if named is going out and fetching the answer each time
c) "how does BIND answer an RRSet with multiple A records? does it 
answer with only 1 IP address of the RRset?". Query 
multiple-ip.5test.com and observe the behavior

                                                                         
- Kevin

Surya ARBY wrote:
> Hello.
>
> I'm sorry, I work on a project which consist to set up a GSLB solution 
> in internal network and in the Internet.
>
> I found these articles :
>
> http://www.tenereillo.com/GSLBPageOfShame.htm
> http://www.tenereillo.com/GSLBPageOfShameII.htm
> http://www.tenereillo.com/BrowserDNSCache.htm
>
> And I wanted to be sure to understand the exact Bind behavior, by 
> asking directly the users. I read the documentation and many links on 
> the Internet, I ask to the users because i work in an environment 
> (enterprise networking) where doc statements and real world are 
> sometimes differents (example, Squid internal DNS cache behavior in 
> real life is not what is described in the doc)
>
> I don't have the time to test it as I dont' have neither the time nor 
> the necessary stuff at work (I don't have 2 Citrix NetScaler and a 
> server on my desk to set up a full GSLB config). I have currently 4 
> other RFP to answer and the next meeting with this customer is next 
> friday morning.
>
> About your comment of this "homework assignment", just type my name in 
> google to check. I thought I could have some help here, I made a mistake.
>
> Regards,
>
> Surya
>
> --- En date de : *Mar 22.7.08, Kevin Darcy /<kcd at chrysler.com>/* a écrit :
>
>     De: Kevin Darcy <kcd at chrysler.com>
>     Objet: Re: Bind internal behavior when used as resolver
>     À: bind-users at isc.org
>     Date: Mardi 22 Juillet 2008, 2h34
>
>     Surya ARBY wrote:
>     > 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 :-)
>     >   
>     Frankly, this sounds like a homework assignment, rather than "real 
>     world" questions.
>
>     I may be wrong on that, if so, pardon the rudeness of my responses, but 
>     the point of studying a subject is to *learn* it, not just copy answers 
>     from other people.
>     >
>     > - By default, does Bind honor the TTL value read in DNS answers ?
>     >   
>     Set up a BIND instance and test this.
>     > - Is it possible to overwrite this TTL value to use another one defined by
>     the local administrator ?
>     >   
>     See max-cache-ttl in the documentation.
>     > - What is the behavior when TTL read is equal to 0 ? Can we be sure it
>     doesn't cache ? 
>     >   
>     Set up a BIND
>      instance and test this.
>     > - Is TTL overwriting often used ?
>     >   
>     N/A.
>     >
>     >
>     > 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 ? 
>     >   
>     Set up a BIND instance and test this.
>     > 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 ?
>     >   
>     Set up a BIND instance and test this.
>     > 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 ? 
>     See rrset-order in the documentation.
>
>                                                                              
>     - Kevin
>
>
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