The DNS iterative resolution feature enables the NetCache full-service resolver (as specified in RFC 1123). The full-service resolver resolves DNS host names on the Internet through iterative queries by traversing the DNS hierarchy. That is, if the DNS server to which NetCache sends the query cannot resolve it, that DNS server takes the responsibility for forwarding the query to another DNS server. The query is forwarded "down" from the root DNS nameserver until the query is resolved.
The full-service resolver caches the results of its queries in the NetCache nameserver cache. NetCache uses cached results to speed lookups.
If the full-service resolver is not enabled, NetCache uses its stub resolver to perform recursive resolution. With recursive resolution, if the DNS server to which NetCache sends a query responds that it cannot resolve the query, NetCache sends the query to a different DNS server. NetCache continues to try different DNS nameservers (one at a time) until the query is resolved.
Enable the full-service resolver (DNS iterative resolution) when you need to reduce the load on your company's internal resolvers. The reason is that the appliance then resolves the majority of host names for the Internet itself.
For Global Request Manager, you can reduce the query load on the back-end nameservers by enabling the DNS Iterative Resolution feature and using it in combination with the Nameserver-to-Domain Mapping option (located on the DNS - General page in the Appliance Manager).
When the NetCache full-service resolver is enabled, the default behavior is that the resolver resolves all queries iteratively except lookups for private IP addresses. Lookups for private IP addresses are always resolved recursively. The reason is that it is assumed that lookups for private IP addresses are local (most companies have private IP addresses). Using iterative resolution for queries outside the company helps to reduce the load on the company's internal DNS nameservers.
The following configuration options on the DNS - General page (Setup tab) in the Appliance Manager are used to configure DNS iterative resolution:
Most companies do not need to configure the Iterative Resolution Forward Query Rules and Iterative Resolution Reverse Query Rules options. The reason is that the NetCache full-service resolver's default behavior alleviates the load on company internal DNS servers. See When you must set forward or reverse query rules for more information.
The following table shows the syntax for the DNS iterative resolution query rules.
{iterate|recurse}
Specifies whether the query will be iterative or recursive.
[!]
Specifies that the iterative or recursive query be carried out on the following:
dnsdomain.
(Forward query rule) Domain name suffix (for example, .org, .com, and .co.uk.) of the host name to be resolved. Network Appliance recommends terminating the domain name suffix specification with a period (.).
subnet
(Reverse query rule) Subnet IP address to be resolved.
You must set one or more query rules for DNS iterative resolution in the following circumstances:
If your company has more than one internal domain, you must list all internal domains in a forward query rule.
For example, if Widget Company uses the domains widget.com, widget.fr, widget.jp internally, then you would list the domains in a forward query rule as follows:
If your company uses globally routable IP addresses internally, you must set a reverse query rule.
The NetCache full-service resolver default behavior is to resolve all queries iteratively except queries for private IP addresses. Therefore, if you are using a globally routeable IP address internally, you must explicitly instruct NetCache that it is a local address.
For example, if Widget Company uses the IP address range 136.43.85.024 and 206.41.0.0/16 internally, you would set the rules as follows:
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Last updated: 11/12/02 16:56:52