Pete Tenereillo pt_bind at
Sun Nov 21 21:52:29 UTC 2004

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----- Original Message ----- 
From: "jesk" <jesk at>
To: <bind-users at>
Sent: Friday, November 19, 2004 11:47 AM
Subject: Failover

> Hello,
> im thinking about a failover setup of webservices at different locations 
> via
> DNS.
> I got some questions about the possibilities of this:
> 1. how is "IN NS" cached and used by other bind nameservers if one of the 
> NS
> is down? f.e. the TLD server has two "IN NS" records for my zone, now a
> nameserver is looking up this zone and will get this 2 records. first i
> think its trying to resolv via the first nameserver of the replyorder, but
> what would be if this one is down and not reachable, will the resolving
> nameserver try to query via the second one a second time? what would be if
> the first nameserver can succesfully answer, then will be cached by the
> resolving nameserver, but then in the future of the life of the cached "IN
> NS" record the nameserver will be down, is the second nameserver still in
> the cache and the failover will work if this will happen?
> 2. is the only solution to get a global dns failover without the use of
> routing protocols like BGP to use two or more nameservers at different
> locations(AS or something else) which will then answer queries f.e. of
> webservers with its own specific A-records? f.e. if nameserver A is down 
> in
> cause of a routing problem, then a resolver will query nameserver 
> B(located
> at a different provider) which then will answer a query for www.domain.tld
> with a specific A-record which will be reachable, because its in the same
> physically network.
> 3. if the "IN NS" failover is possible, whats about caching nameservers
> which are caching A-records? are them also failover possible, if yes would
> it be possible to return the A-records for the webserver of both locations
> so that a client will try webserver A first and when not reachable 
> webserver
> B (i think its a implementation thing and too much risk)? or is the only
> solution to create a zone with a TTL of zero?
> thanks for any hints and explanations to get this fully understanding :)
> best regards,
> christian

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