If you expect that users will enter domain names that are not fully qualified, you should configure NetCache to handle such names. Users in enterprises usually know that they can enter partially qualified domain names in URLs. Therefore, system administrators of enterprises should consider configuring NetCache to handle domain names that are not fully qualified.
ISPs, as a rule, do not need to configure support for domain names that are not fully qualified because their users typically enter fully qualified domain names in URLs.
The following options on the DNS - General page in the Appliance Manager can be configured to handle domain names that are not fully qualified:
Enables and disables NetCache performing a domain tree search for DNS lookups. When this option is enabled, NetCache uses the paths specified in the DNS Search Paths option, and DNS lookups occur even if the domain name is fully qualified. Keep in mind that a domain-tree search can generate a large amount of network traffic if the servers for the listed domains are not local.
Identifies the paths that NetCache should follow when trying to resolve a host name. NetCache follows the order in which the search paths are listed in this option, from the top to the bottom of the list.
By default, when NetCache looks up a domain name in its DNS cache, NetCache first attempts to look up the domain name with the local domain name appended, even if the requested domain name is fully qualified. If the first lookup fails, the NetCache DNS resolver then performs a lookup without the local domain name appended. The result is that the resolver performs an extra lookup when the URL contains a fully qualified domain name.
Note
The concept of fully qualified differs between DNS and most application-level protocols. For DNS, a domain name is fully qualified only if a dot appears at the end of the domain name. For example, although www.books.com appears to be a fully qualified URL, it is not fully qualified according to the DNS specification because no dot appears at the end. For this reason, NetCache appends the local domain name to the domain name.
If you expect that your users will always provide fully qualified domain names, Network Appliance recommends that you do not enable the DNS Tree-Search Enable option. The reason is that when the DNS Tree-Search Enable option is enabled, a DNS lookup occurs even if the domain name is fully qualified.
Avoiding an extra DNS lookup can be beneficial for the following reasons:
The following table describes what occurs for domain names when the DNS Tree-Search Enable option is enabled. Assume for this example that the local domain is books.com and a valid host name is web.books.com.
The following table describes what occurs for domain names when the DNS Tree-Search Enable option is disabled. Assume for this example that the local domain is books.com and a valid host name is web.books.com.
By configuring the DNS Search Paths option, you increase the probability that NetCache can successfully resolve a host name if the domain name in the URL is not fully qualified. The reason is that NetCache can expand its search beyond the local domain. When the DNS Search Paths option is configured, NetCache tries to resolve the host name by searching in the following order:
Identify DNS search paths if you have enabled the DNS Tree-Search Enable option.
Note
Network Appliance recommends that you determine the most commonly looked-up host names and list those first. The reason is that NetCache does not continue searching after it makes a match (which optimizes performance).
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Part No. 210-00317
File: dns6.htm
Last updated: 11/12/02 16:56:52