DNS - Caching server startup

[u856100]

Hi all,

I am currently in the middle of setting up DNS on a system and was a bit curious about the behaviour of the caching server should other DNS servers crash.

I have configured the secondary DNS server using the boot.sec.save file so that data base files will be saved to local disk, hence ensuring boot up should the system go down and the primary fail to start. But what would happen to the caching server in this scenario? is this server able to start if the primary is down but the secondary is up?

any help, suggestions towards obtaining a resolve would be much appreciated,

thanks guys and gals

john

[Sachin Patel]

U85???

I belive if you have /etc/nsswitch.conf file configure as
hosts: files [NOTFOUND=continue] dns
then you will not have any problem.

Sachin

[Christopher Caldwell · Accepted solution]

In a truly caching only name server, the server isn't authoritative for any names. You add the "root zone" as a database stub file. The caching server uses the root zone to build [cache] names that you control and names that you don't control. True caching name servers save time by locally caching queries; these servers don't perform zone transfers.

In the case of a secondary name server, you add zones for which you are authoritative to the primary (master) server. The secondary name server uses zone transfers to copy the zones to local files (and cache the zones in memory).

If the primary (master) server disappears, the secondary server won't know it, unless
1) you restart the secondary name server
or
2) the primary is down for more than "refresh" seconds.

The tunes are as follows:
1) refresh - how often a secondary checks whether it's data is up to date.
2) retry - refresh after the first failure to reach a primary (master).
3) expire - how long to keep data when the primary (master) isn't available.

Though the secondary will provide diagnostic when the primary isn't available, the secondary won't fail to return resource records until the primary isn't available for expire seconds.

[U.SivaKumar_2]

hi,
In case of caching server , you can manage with non-authoritative replies up to the time the cache server refreshes depending upon the
TTL of the records, it had cached.

regards,
U.SivaKumar

[Bill Thorsteinson]

As you have configured the
server to save the files to
disk, it will be able to
start. For domains that it is
configured as secondary for it
will be able to provide
information at least until it
expires. As it has files for these domains it may rely on
the files until the primary
is available.

For domains that you wish to
secure there is a flag which
will make the caching server
return authorative answers.
This will prevent your clients
from searching elsewhere for
authoriative answers, and
allows you to limit DNS access
to the caching server.