DNS Caching

By now, you must have realized that this is nowhere near efficient enough. To query the root nodes every time you want to browse www.google.com.hk would be extremely taxing on the root DNS servers. You have seen the output of dig; there can be quite a bit of information for one web site alone. Now multiply that by the number of web sites on the Internet and then again by the number of people who browse the net. Take that number and multiply again for every Smartphone, nettop (Internet desktop), and Internet-enabled device out there. Needless to say, it’s quite a lot.

Although all of the core DNS servers are actually clusters of servers that respond to queries as a group (which gives them a lot of power and bandwidth), it’s still nowhere near enough to power every single DNS query for the whole planet! The solution is called caching. Caching means that your system will keep its own list of known servers and DNS servers to allow it to look them up from its own storage. This cuts down on the amount of time it would take to do a full walk of the DNS tree for a server you have visited before. It also reduces the number of queries sent to the primary nodes. For example, our server that has been doing the dig lookups of www.google.com.hk will already have in its memory the nameserver for the hk domain that it has looked up and the DNS entry for Google.