BIND 9.7 behavior - lack of response causes

[Mark Andrews]

What do you have lame-ttl set to?

In message <361220.19486.qm at web121407.mail.ne1.yahoo.com>, Fr34k writes:
> Hello,
> 
> Given:  BIND 9.7.2-P2 on Solaris 10.
> 
> For about an hour, I had a network event where a caching DNS server could not
>  
> get recursive queries back from authoritative DNS servers on the Internet.
> 
> Obviously, this is a problem.
> 
> Moreover, the authority for our most popular hostnames have set very low TTLs
>  
> (less than a minute), so nothing in cache for the server to call upon during 
> this hour long event.
> 
> Yuck.
> 
> A snoop of port 53 traffic at the time shows client PCs requested hostname 
> resolution -- as they would normally do.
> 
> Now, for the interesting part.
> 
> >From the same snoop of traffic, the caching DNS server did not send ANY resp
> onse 
> back to these PC clients for these low TTL popular hostnames.
> 
> Keep in mind that I did snoop until *after* the event started.
> 
> So, it may be the case that some BIND mechanism was behaving appropriate for 
> queries which it could not act upon.  I can appreciate that BIND makes decisi
> ons 
> with network performance in mind.
> 
> In my attempts to understand negative caching, Sections 7.1 and 7.2 of RFC 23
> 08 
> list Server Failure and Dead / Unreachable Server as "(OPTIONAL)" utilities.
> 
> Bind 9.7 ARM says that "the server stores negative answers" for (default) 3 
> hours; however, I'm not sure what the expected BIND behavior is.
> 
> Would some mechanism, such has max-ncache-ttl or clients-per-query, be 
> responsible for this lack of return traffic?
> 
> Anyone have ideas to share?
> 
> Thank you.
> 
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-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org