DNS and Reversed DNS

Before I start talking about how to configure DNS, you need to know about reversed DNS. Translating names into IP addresses is one task of the DNS server; the other task is translating IP addresses to names. This is called reversed DNS, and it is necessary if you want names instead of IP addresses. This feature, for example, is useful if you want names in your log files instead of IP addresses. Although useful, you should realize that you pay a performance price if you want all IP addresses translated to names. To make this work, you need to set up reversed DNS.

To create a reversed DNS structure, you need to configure the in-addr.arpa domain. Under that domain, a structure is created that contains the inversed IP addresses for your network. For example, if you are using the class C network 201.10.19.0/24, you should create a DNS domain with the name 19.10.201.in-addr.arpa. Within that zone, you next have to create a PTR resource record for all the hosts you want to include in the DNS hierarchy.

When working with reversed DNS, you should be aware of one important limitation: it doesn't know how to handle nondefault subnet masks. This means it works only if you have the complete network and not if you have registered a couple of IP addresses only with your Internet provider.

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