is NS record pointing to "some other name server" needed in case of classless IN-ADDR.ARPA delegations?

[Mark Andrews]

If a zone is being made available to the public (which these are)
then steps should be taken to ensure it is resolvable all the time.
This means having multiple servers that are not subject to common
failures.  This is basic DNS.

In message <CAJx5YvE43cTiNmw+AEun01pAig3kjK8D+4TBhVAwYhUiqgNt7g at mail.gmail.com>, Martin T writes:
> Hi,
> 
> in case of classless IN-ADDR.ARPA
> delegations(http://www.ietf.org/rfc/rfc2317.txt) I have usually seen
> at least one NS record pointing to name server other than the
> end-customer ones. Example from rfc2317.txt where there are two NS
> records and the second one is not the end-customer name server:
> 
> 
> ;  <<0-127>> /25
> 0/25            NS      ns.A.domain.
> 0/25            NS      some.other.name.server.
> ;
> 1               CNAME   1.0/25.2.0.192.in-addr.arpa.
> 2               CNAME   2.0/25.2.0.192.in-addr.arpa.
> 3               CNAME   3.0/25.2.0.192.in-addr.arpa.
> ;
> 
> 
> Another example from one real name server zone file:
> 
> ;
> 0               IN      NS      ns.content-providerA.com.
> 0               IN      NS      ns2.content-providerA.com.
> 0               IN      NS      ns.isp-of-content-providerA.net.
> ;
> 1               IN      CNAME   1.0.47.168.192.in-addr.arpa.
> 2               IN      CNAME   2.0.47.168.192.in-addr.arpa.
> 3               IN      CNAME   3.0.47.168.192.in-addr.arpa.
> ;
> 
> Is NS record pointing to "some other name server" needed in case of
> classless IN-ADDR.ARPA delegations? What happens if one does not
> specify this?
> 
> 
> regards,
> Martin
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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