Data caching of responses to Domain Name System (DNS) queries is done by i5/OS™ sockets in an effort to lessen the amount of network traffic. The cache is added to and updated as needed.
If RES_AAONLY (authoritative answers only) is set in _res.options, the query is always sent on the network. In this case, the cache is never checked for the answer. If RES_AAONLY is not set, the cache is checked for an answer to the query before any attempt to send it on the network is performed. If the answer is found and the time to live has not expired, the answer is returned to the user as the answer to the query. If the time to live has expired, the entry is removed, and the query is sent on the network. Also, if the answer is not found in the cache, the query is sent on the network.
Answers from the network are cached if the responses are authoritative. Non-authoritative answers are not cached. Also, responses received as a result of an inverse query are not cached. You can clear this cache by updating the DNS configuration with either the CHGTCPDMN, CFGTCP option 12, or through iSeries™ Navigator.