DNS

This paper assumes that the reader knows the details of name lookup as they stood in 1988, which makes it somewhat difficult to understand the finer details of the paper. Below is my best attempt at understanding this paper.

The problems with the existing system, which was a HOSTS.txt file, were twofold. First, the file was growing large and unwieldy. Second, the administrative difficulties associated with the file were growing more than linearly. As a result, the DNS system was proposed.

DNS consists of multiple zones. Each zone is responsible for DNS lookups within its own zone. DNS supports multiple levels of hierarchy by allowing each zone to delegate sub-zones, which are also responsible for their own DNS lookups. This has the advantage of allowing different organizations to have different number of levels within their naming schemes. Each sub-zone gets a label, which can be a collection of 8-bit values. The length of a label cannot exceed 63 values, and the total length cannot exceed 256 such values (though apparently, those maximums are subject to change).

The DNS system consists of both DNS servers and DNS resolvers. The choice to separate these two systems stems from the fact that the storage of data and the protocols for accessing it should be different. The servers store data, whereas the resolvers implement the algorithms that enable them to access and distribute the data. In other words, different resolvers can be used throughout different systems so as to better serve the end-users, who may have a wide variety of operating systems or architectures.

One of the most interesting things about this paper is that they specifically took into consideration the difficulty of adopting DNS. They decided to use a relatively lightweight system so as not to discourage people from using DNS. They also wanted the system to be easily extensible; these two goals lead to a delicate balancing act.

I think the most interesting part of this paper is the part where they discuss failures. In particular, the tendency of system administrators to just copy examples out of the documentation, or to make mistakes (such as switching the identifier and TTL fields), led to incredibly poor performance across the system. Furthermore, their desire to simply get a system that worked, rather than a system that worked well, undermined the efforts of the DNS designers. In particular, system administrators would apparently not have their top level servers in different networks, but claimed that they were not a single point of failure anyway.