What would be happen if one of two dns was down?

[MontyRee]

So thanks for kind and concrete answers.
 
and addtional questions are... 
 
 
-. others can use other resolvers like windows based or other bind version.
    so this program works well as you said without exception?
 
 
-. in the point of high-availability of service,
   what it better two authorative dns servers or two master dns servers using L4 switch?
 
 
 
So thanks again.
 
 
Regards.
 
> Subject: RE: What would be happen if one of two dns was down?> From: chris_cox at stercomm.com> To: bind-users at isc.org> Date: Tue, 12 Aug 2008 10:44:02 -0500> > On Tue, 2008-08-12 at 06:42 +0000, MontyRee wrote:> > So thanks for kind answer.> > > > > > Additional questions below.> > > > > > >> Hello, all.> > >>> > >>> > >> I have operated two dns(primary and secondary) for one domain like below.> > >>> > >>> > >> example.com IN NS ns1.example.com> > >> example.com IN NS ns2.example.com> > >>> > >>> > >> and there was a event that ns1.example.com dns was down.> > >> As I know, if ns1 dns is down, all requests go to the ns2.example.com.> > >> > > Depending on what 'down' means, it could take some time before> > > the request is sent to ns2. So there will likely be a delay, even> > > if not much (it will feel like forever to some users).> > > > > > my 'down' means that system down so can't ping to server.> > > > > > >> But when ns1.example.com dns was down, actually some people c
 an't lookup the domain.> > >> > > Sounds like a configuration issue. However realize there is a zone> > > cache and if ns2 is slaving zones of ns2 (typical bind master slave> > > scenario) and the zone cache expires, then ns2 will refuse to> > > trust the slaved zone it had... and thus nothing works.> > > > > > Sorry, I can't understand what you said.> > actually the master dns server(system) down time was just a hour and slave dns> > works well without any problem, but at that time some can connect but some said that> > they can't resolve the domain at all.> > The slave will answer queries for the zone until the zone TTL expires> in which case if cannot contact the master, the zone will go effectively> dead.> > I think I used some bad "terms" in my explanation. Basically> there is an expiration ttl for which a slave will consider its> data to be good. After that, it will need to hit the master.> > (I trip up on using the right words)> > The value is often set to 2 weeks or 
 more. But if the master is> down for a LONG time... you'll lose it all eventually (the slave> won't answer for that zone anymore).> > If you're seeing this problem after a short period of time, that's> likely NOT the cause unless somebody set the expiry in the SOA> to something really small.> > Caching in DNS is a wonderful thing, but can cause scenarios where> resolution is working for one and not for another (because of> the various Time To Live values and the time of last query/cache).> > Can you give us a feel for the amount of time between the failure> and the problem? Is it almost immediate? If so, then it's some> other kind of configuration issue (unless, as I said the zone was> just totally miconfigured). Can you post the SOA for the zone?> > > > > > > It means, dns failover doesn't works well?> > and some resolver or some bind version, insist querying for the downed dns server?> > Usually the client resolver is looking to query multiple nameservers, if> the first on
 e is down, it moves onto the next and so on. Failover works> fine in this style (normally). Of course, a client might NOT be aware> of more than one nameserver... in which case there is no failover (duh).> > > ...> > > > So thanks for your help again..> > Did I explain it better this time?> > 
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