Universal Acceptance of TLDs
----------------------------

As ICANN has introduced new generic Top Level Domains into the DNS
root, problems have been experienced with end users receiving errors
from applications which try to sense the validity of a domain name.
Traditionally all top-level domains have either been two octets long
(for country-code top level domains like .UK and .DE), or three octets
long (for generic top level domains like .COM and .INT). However, with
the introduction of new domains such as .INFO and .TRAVEL this premise
should no longer apply.

This project seeks to educate software implementors to use more robust
techniques to validate the existence of a top-level domain name.

Ideally, if it is essential to an application to verify the existence
of a domain, it should perform a DNS enquiry to see if the domain
exists. This is the only test that can positively identify availability,
although it is worth noting that due to transient network issues, some
domains may not be visible from all locations at all times.

If the aim of the test is purely to identify if the top-level domain
is valid, rather than the entire host name, a similar test can be
conducted against the DNS root servers to identify if the domain has
been delegated.

Finally, in certain applications - such as those without reliable
connectivity to perform live DNS requests, or for those for performance
reasons can not conduct such requests for each test, the possibility
exists to verify against a list of know good TLDs. An implementor of
this technique MUST ensure the application routinely updates this list,
as new domains can come into existance, and old domains disappear. As
the reason this problem exists is due to dated assumptions about valid
domains, developers MUST NOT deploy a system using a fixed list that
doesn't have mechanisms to update that list on a routine basis.

We have developed a small library for a variety of development platforms
for implementers of these three techniques. Each has the following
approximate functions:

verifytld(domain):

    Verifies a top-level domain exists.

    This function takes a single argument, which can either be a
    domain name, or a TLD - and verifies its validity using the DNS
    protocol.

verifytldoffline(domain[, filename]):

    Verifies a top-level domain exists against a fixed database.

    The first argument supplies is either a domain name, or a TLD,
    which is verified for validity against a fixed database that
    has been previously obtained with the refreshtlddb() function.
    The optional second argument is the filename where the cache
    is stored.

refreshtlddb([filename]):

    Updates the copy of the fixed database of valid top-level
    domains.

    Downloads the official list of valid TLDs from the IANA website,
    and performs consistency checking to ensure it was downloaded
    correctly. The optional argument is the filename to store
    the cache in.

    NOTE: This function should not be called on every request or 
    invocation, it is designed to store a cached version of the file, 
    which can be referenced in future queries. There is no need to 
    update this file more often than once per day.



Information References
----------------------
1. http://www.rfc-editor.org/rfc/rfc3696.txt

4 December 2006