NetCache as a DNS proxy cache

Problems with querying DNS nameservers

Typically, clients send DNS queries to a DNS nameserver for host name resolution. Common complaints about queries to DNS nameservers are as follows:

DNS lookups are slow because nameservers are overloaded.
If a DNS nameserver is not located close to a client, significant bandwidth can be consumed by sending DNS queries to remote servers.
Nameservers are often misconfigured with incorrect entries.

How DNS caching works

You can expand the DNS capability of NetCache by configuring a NetCache appliance to function as a DNS proxy cache for use by clients. Clients send DNS queries to the NetCache appliance. If the appliance has the host name to IP addresses mapping in its cache, it can resolve the DNS query without contacting the DNS nameserver. If the appliance cannot resolve a DNS query, it contacts a DNS nameserver to resolve the query, caches the host name and IP addresses resulting from the query, and returns the host's IP addresses to the client.

Note
NetCache always caches the results of lookups that it initiated and sent to a DNS nameserver. (DNS nameservers are identified in the Nameservers option on the DNS - General page in the Appliance Manager.) NetCache then serves the host's IP address for NetCache internal processes without having to query the DNS nameserver with subsequent requests for the same host name. This type of DNS caching is not configurable.

Advantages of NetCache as a DNS cache for clients

The advantages of enabling DNS caching on a NetCache appliance are as follows:

Reduced load on remote nameservers because the NetCache appliance can perform DNS name lookups on their behalf
Reduced response time for DNS lookups when a NetCache appliance is deployed closer to the clients than the nameservers
Reduced bandwidth usage

What NetCache caches

NetCache caches the results of A (answer) type and PTR (pointer) type queries, the result of which can contain the following:

A host name to IP addresses mapping
A CNAME record, which represents the aliases for a given host name
An IP address to host name mapping
A PTR record, which represents the aliases for a given host name

DNS cache is only in memory

NetCache saves the results of A type queries only in memory. When the NetCache appliance reboots, the DNS cache is cleared.

What NetCache proxies

NetCache proxies all non-A type and non-B type queries to the DNS nameserver on behalf of the client.

Requirement if the client access method is nontransparent

You can set up DNS caching regardless of the method that you have set up for clients to access the NetCache appliance. However, if your organization's client access method to this NetCache appliance is nontransparent, you must do the following in addition to enabling DNS caching:

For UNIX, add the NetCache appliance to the list of nameservers in the etc/resolv.conf file on the client.
For Windows NT, add the NetCache appliance to the Control Panel > Network > Protocols dialog box.
For other operating systems, see your operating system documentation.

Length of time DNS lookups remain in the DNS cache

For a given response to a DNS query, NetCache saves the shortest expiry time of all the records in the response as the expiration time.