Forwarders and Slaves

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Forwarders and Slaves

When a client contacts a DNS Server for name resolution, the DNS Server first looks in its local files to resolve the request. If the DNS Server is not authoritative for the zone pertaining to that request, it must look to another name server to resolve the request. When you are browsing the World Wide Web, resolving a domain name involves either making a request of a name server maintained by your ISP or going on the Internet to contact a name server there.

You may not want all DNS Servers to forward these requests. Thus DNS enables you to designate specific DNS Servers as forwarders. In general, only forwarders can communicate on the Internet or beyond the local network. The other DNS Servers are configured with the address of the forwarder. The forwarder is much like a gatekeeper, to which all outside requests are funneled. You can put some firewall software or other protective measures on the forwarder without having to do so to all the DNS Servers in your organization. An entire server is designated as a forwarder; this is not done on a zone-by-zone basis.

When a forwarder receives a request to resolve a name, it accesses outside resources and returns the response to the DNS Server that originated the request. If the forwarder can’t answer the request, then the originating DNS Server can resort to other means to resolve the request.

Slaves are DNS Servers configured to use forwarders and also configured to return a failure message if the forwarder can’t resolve the request. A slave does not try to contact other DNS Servers if its designated forwarder can’t handle the request. In other words, a slave makes a recursive query to a forwarder.

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