Thursday, September 11, 2008

DNS: Recursion

Link for below article:

DNS: The difference between "Do Not Use Recursion" and "Disable Recursion"

In the Windows 2000/2003 DNS console (dnsmgmt.msc), under a server's Properties -> Forwarders tab is the setting Do not use recursion for this domain. On the Advanced tab you will find the confusingly similar option Disable recursion (also disables forwarders).

Recursion refers to the action of a DNS server querying additional DNS servers (e.g. local ISP DNS or the root DNS servers) to resolve queries that it cannot resolve from its own database. So what is the difference between these settings?

The DNS server will attempt to resolve the name locally, then will forward requests to any DNS servers specified as forwarders. If Do not use recursion for this domain is enabled, the DNS server will pass the query on to forwarders, but will not recursively query any other DNS servers (e.g. external DNS servers) if the forwarders cannot resolve the query.

If Disable recursion (also disables forwarders) is set, the server will attempt to resolve a query from its own database only. It will not query any additional servers.

If neither of these options is set, the server will attempt to resolve queries normally:... the local database is queried... if an entry is not found, the request is passed to any forwarders that are set... if no forwarders are set, the server will query servers on the Root Hints tab to resolve queries beginning at the root domains.