Telecom service providers can configure the NetScaler appliance to function as a DNS proxy. Caching of DNS records, which is an important function of a DNS proxy, is enabled by default on the NetScaler appliance. This enables the NetScaler to provide quick responses for repeated translations and hence enhances the customer experience and also saves the bandwidth. The caches responses from DNS name servers. When the appliance receives a DNS query, it checks for the queried domain in its cache. If the address for the queried domain is present in its cache, the NetScaler returns the corresponding address to the client. Otherwise, it forwards the query to a DNS name server that checks for the availability of the address and returns it to the NetScaler. The NetScaler then returns the address to the client.
For requests for a domain that has been cached earlier, the NetScaler serves the Address record of the domain from the cache without querying the configured DNS server and hence saves the bandwidth.
From 11.0 release onwards, NetScaler also logs the DNS requests that it receives and also the responses that it sends to the client. Telecom service providers can use this log to:
- Audit the DNS responses to the client
- Audit DNS clients
- Detect and prevent DNS attacks