Hints for Exercises: Chapter 8

  1. Look up ISO3166 and determine the latest country code additions to the DNS. Similarly investigate the latest generic TLDs.

    Links. Country codes don't change very often, but je for Jersey is fairly new. New generic TLDs include aero, coop, jobs, mobi, pro.

  2. The precise locations of the root servers are kept secret for security reasons. Use traceroute (or other) to get a rough idea of where in the world some of them might be situated.

    Root name servers are named a.root-servers.net through m.root-servers.net, and each name refers to several machines. See here for more information.

  3. DNS is a simple distributed database, designed for a specific purpose. Find out about other kinds of distributed database and discuss whether they could be a suitable replacement for DNS.

    LDAP is the most obvious example. DNS is a hierarchical database and most lookups are referrals to other parts of the database, which means that ownership of data is widely spread. In other databases the emphasis generally is on keeping to a minimum number of steps between request and data, so that the opportunities for distributing data are lessened.

    Also, DNS is very specialised, while others generally have more flexible means of indexing into the database, such as using search patterns or compound queries ("all records such that X and Y but not Z"). This mean DNS is optimised for its purpose and will usually be faster.

  4. Make notes on the various kinds of record that DNS supports. How many are in common use?

    Links. Most common are A, PTR and MX. Behind the scenes is AFXR for zone transfers. AAAA will become more important, as should the records for security and authentication. Other emergent services like SPF will use TXT and service discovery will use SRV.

  5. Determine how to host a DNS name, both on your own machine and using a commercial hosting service.

    Both BIND and djbdns are widely used and documented, but many others are available.

    DNS hosting from a commercial service is very easy, just the application of a little money is enough. Though you should beware of the different terms and conditions of different companies.

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