14.10 Summary

14.10 Summary

The DNS is an essential part of any host connected to the Internet, and widely used in private internets also. The basic organization is a hierarchical tree that forms the DNS name space.

Applications contact resolvers to convert a hostname to an IP address, and vice versa. Resolvers then contact a local name server, and this server may contact one of the root servers or other servers to fulfill the request.

All DNS queries and responses have the same message format. This message contains questions and possibly answer resource records (RRs), authority RRs, and additional RRs. We saw numerous examples, showing the resolver configuration file and some of the DNS optimizations: pointers to domain names (to reduce the size of messages), caching, the in-addr.arpa domain (to look up a name given an IP address), and returning additional RRs (to save the requestor from issuing another query).