Crash of NIS Server Generates Unusual DNS Query Traffic

We investigated statistically on the unusual DNS query traffic from several DNS clients like Linux servers and/or PC terminals in the campus network of a university. The interesting results are: (1) The DNS query traffic includes several keywords relating with database servers in the local area network, to which the Linux servers and PC terminals are belonging. (2) These keywords are generated by network information system (NIS) server program daemons in the database servers. Recent NIS communication employs the remote procedure call (RPC) with libwrap that performs name resolution to the DNS server. From these results, we can reasonably take a workaround to refrain the unusual DNS query traffic when configuring host domain names and their IP addresses in the /etc/hosts file.