Elegant Use of DNS

Liberal use of HINFO and TXT fields

DNS can carry much more information about a machine than just the IP address. By specifying the machine's hardware and operating system type in the HINFO field, and by including useful information in TXT fields, one can have information about machines always at hand, as well as assist others trying to debug problems. By including information about the machine's user in TXT fields, Internet users can determine who is responsible for a particular machine. For example, the records for the machine "hobbes.gtlug.org" are:

hobbes          IN      A               130.18.92.25
                IN      MX      10      hobbes
                IN      MX      20      Dune.EE.MsState.Edu.
                IN      HINFO   i486/66 Linux
                IN      TXT             "David L. Simmons"
                IN      TXT             "1 Research Boulevard"
                IN      TXT             "Starkville, MS"
                IN      TXT             "(601) 324-xxxx"

If something goes wrong on this machine, and it starts interfering with a machine elsewhere on the Internet, people will know who to contact to get the problem corrected. TXT fields can also be provided for parent domains as well, so that users can query them to get more useful information:

$ host -t txt gtlug.org
gtlug.org descriptive text "Golden Triangle Linux Users Group"
gtlug.org descriptive text "Advancing Society Through Linux"
gtlug.org descriptive text "http://www.gtlug.org/"

Many institutions use the TXT fields for recording other information such as ethernet addresses, and use scripts to generate their "ethers" file and bootp tables from the zone information. This allows the information about machines to be kept in a single file, minimizing administrative overhead. Refer to RFC1464 for one possible scheme for accomplishing this.

Static IP Addresses for dialup users

In these crazy days where IP address depletion ranks up there with global warming and the destruction of the rain forests, assigning a static IP address for every dialup user may seem insane. However, if the address space is available, this can be a tremendous convenience to everybody. Each user of the dialup facility can be assigned an IP address to be used for the duration of the account, along with an appropriate domain name, in the form of "username.myprovider.com" perhaps. Combine this with the use of appropriate HINFO and TXT fields as mentioned above, and each IP address gains a concrete identity associated with it.

Many local providers are able to obtain a block of 16 or so class C networks from their backbone provider's CIDR block, enabling them to assign IP addresses in this manner. Also, some university facilities are beginning to use this system to reduce the danger of "anonymous" IP sources from their dial-ins.

Use of two-letter domains

The use of two-letter domain names is dangerous, especially when they match a two-letter ISO country code used for a top-level domain. This is because a very few systems read fully qualified domain names backwards, and mail sent to "uk.foobar.de" may be sent to England instead of Germany. This contorting of domain names can mostly be blamed on the old JANET-style naming system once (still?) used in the United Kingdom.

Last modified: April 10, 2003 02:58:41 UTC
David Simmons
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