Nalanda

Citations:

Mockapetris, P. and Dunlap, K. J. 1988. Development of the domain name system. SIGCOMM Comput. Commun. Rev. 18, 4 (Aug. 1988), 123-133. DOI=http://doi.acm.org/10.1145/52325.52338

Jung, J., Sit, E., Balakrishnan, H., and Morris, R. 2001. DNS performance and the effectiveness of caching. In Proceedings of the 1st ACM SIGCOMM Workshop on internet Measurement (San Francisco, California, USA, November 01 - 02, 2001). IMW ‘01. ACM, New York, NY, 153-167. DOI=http://doi.acm.org/10.1145/505202.505223

These two papers provide interesting views into the process of design of DNS, and of actual measurements of those design choices.

DNS was originally created to address problems with the HOSTS.TXT approach to maintaining host name to IP address mappings: the technical problem that the file was growing too large with increasing numbers of hosts, and the administrative problem that it was becoming difficult to maintain a single master file as the number of independent administrations on the network increased. To address these problems, a hierarchical system was created, with different servers accounting for different sections of the DNS tree. Administrations could maintain authoritative servers for their own domains, while higher level servers, leading up to the root servers, could provide pointers to tie the different administrations together.

It was interesting to see how many of the problems mentioned in the first paper were social, rather than technical: the difficulty of introducing new classes (which seems to me unrelated to DNS itself), the incentives for transitioning HOSTS.TXT-based to DNS, explicit requirements for redundancy in all DNS servers (which seems unachievable at Internet-scale), following sample settings word-for-word.

The first paper presents caching as one of the successes of DNS, in the context of the “unexpectedly bad performance” of the Internet of the time. Without caching, the DNS system may have been doomed to failure, making wider adoption more difficult. The second paper calls caching into question, specifically with reference to the predominant web traffic on the networks sampled.

As the second paper observes, most wide area traffic is web traffic, where a cluster of requests to a server are preceded by a single lookup. Since the distribution of names is Zipf-like, the usefulness of caching for A records is limited. The evaluation in this paper suggests that small groups of clients, of the order of 25 or so, provide the benefits of caching close to providing a common cache across all clients. However, since HTTP 1.1 is now fairly widely deployed, it seems likely that there the correspondence of TCP to DNS flows will be closer to 1:1, which begs the question whether caching of A records provides any utility today.

The authors also show that caching of NS records provides important performance benefits, as it reduces the number of referrals per lookup, and also reduces the load on the root and gTLD servers. This make intuitive sense; I would imagine the hierarchy of DNS servers to be relatively stable, which would lend itself well to caching with large TTL values.