Loading Factors for DNS Systems

Administrators of DNS are very considerate of the mission-critical nature of these systems. A high CPU load factor on a name server would be cause for concern. So, naturally, the administrators frown upon an NNM system sending bursts of DNS requests in the hundreds-per-second range all day long. Fortunately, DNS is very efficiently implemented. All network queries arrive inside lightweight UDP packets and all replies are satisfied either from RAM cache or from another name server. Only simple operations are performed, and just a little data is transmitted. Disk I/O is created only when named must refresh a domain, restart, dump its database, swap, or write a syslog message. You definitely want to provision enough RAM to always keep named in memory.

To address the perception that the DNS server might be overloaded, it is prudent to run a caching-only name server on the NNM system. A caching-only name server has no authoritative database files, refers unknown lookups to the name servers listed in its db.cache file, and returns lookups from its RAM cache.