Bind internal behavior when used as resolver
Kevin Darcy
kcd at chrysler.com
Tue Jul 22 22:02:14 UTC 2008
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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