fallback to forwarder if master zone does not have requested record

Chuck Swiger cswiger at mac.com
Thu Oct 13 15:51:17 UTC 2011

On Oct 13, 2011, at 7:57 AM, Moser, Stefan (SIDB) wrote:
> in customer migrations, when we shift customers from an old DNS environment to a new DNS environment, there are sometimes situations where we have to keep the same domain (let’s say “example.com”) both on the old DNS-server and on the new DNS-server. E.g., there was an A record “mail.example.com” on the old DNS-server “dns-old”, and an A record “sap.example.com” on the new DNS-Server “dns-new”. It would be beneficial, if DNS-clients of “dns-new” could resolve both “mail.example.com” and “sap.example.com”, across both DNS-servers.

One could do this by having "dns-old" switch to being a slave of the zone from "dns-new".

Or remove any trace of configuration of "example.com" zone from "dns-old", and clients talking to "dns-old" will have it perform recursive resolution of the domain which will get data from "dns-new", just as it would for any other random domain.

> I can’t think of a meaningful BIND configuration to “mix” both zones, because of the inherent zone / authoritative model that DNS and BIND have and that makes forwarders, masters and slaves mutually exclusive. What would be needed was some kind of “fallback forwarder” that would forward requests it cannot find in a zone that it is authoritative for.

Um, yeah.  If you configure a nameserver to be authoritative for a zone, then that zone needs to have every valid record.  If an authoritative nameserver doesn't have all valid records, someone is doing it wrong.


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