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Providing the Wrong Location: The presence of alternate public DNS roots can result in different answers being
given to the same DNS query issued from different computers on the Internet, depending on whether the inquiring computer is
programmed to access the authoritative root or a particular one of the alternate roots (or more precisely a domain-name
resolver associated with one or the other of these). The fundamental DNS design goal of providing consistent answers to DNS
queries is therefore frustrated.[1]
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Reaching the Wrong Computer: The main consequence of such inconsistent data is that the same domain name can
identify different computers depending on where the name is used. Put another way, Uniform Resource Locators (URLs)
are no longer uniform. Thus, typing in a Web site address at two different computers configured to reference different roots
can result in reaching different Web sites—a particularly disturbing possibility if, for example, money is to change hands or
privacy or security concerns are violated. Similarly, the same piece of e-mail sent to the same address from the two
computers can be directed to different recipients. The return of inconsistent DNS data defeats the globally consistent
resolution of domain names that is vital to the Internet achieving its promise as a universal communications and applications
medium for commerce, research, education, cultural exchange, expressive activities, and other uses.
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Consequences Unpredictable to Most Users: The set of DNS answers that will be received (from the authoritative root or one of the several alternate
roots) is not predictable by most end users. Most users on the Internet employ a local DNS resolver that is configured by another person. Few users are likely to
appreciate the significance of the resolver's DNS configuration; even fewer are likely to have detailed knowledge of that configuration. As the number of users
on the Internet has grown, the proportion of users knowledgeable about technical concepts such as DNS resolvers and root servers has diminished. Yet these
non-technical users are precisely those for whom the Internet in general—and the DNS in particular—hold the greatest potential benefits.
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Intermediate Hosts Add to Confusion: Moreover, some Internet services depend on the actions of DNS resolvers
employed by intermediate hosts. Alternate roots introduce the possibility that the DNS answer obtained by the intermediate
host alters the character of the service in an unexpected way. A similar phenomenon can occur where one user sends another a
reference to a URL, such as an e-mail reply address or a link on a Web site. If the recipient of an e-mail or the visitor to
the Web site is using a computer that employs a different DNS root than intended by the sender of the e-mail or the designer
of the Web site, unexpected results are likely to occur. For example, the e-mail could end up with the wrong person.
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Cache Poisoning: Alternate roots also introduce the possibility of misdirected Internet activities due to the
phenomenon known as cache poisoning. For performance reasons, the DNS design calls for resource records to be passed around
among the nameservers on the Internet, so that a resolver can obtain quicker access to a local copy of the resource record.
Because the DNS assumes a single-root system, resource records are not marked to distinguish them according to the root from
which they emanate. Thus, the presence of alternate roots introduces the possibility that Internet activities by those
intending to use the authoritative root could be misdirected by a stray resource record emanating from an alternate root.
Indeed, some malicious hacking attacks have been based on this principle, prompting the Internet Engineering Task
Force (IETF) to propose a series of not-yet-fully-implemented improvements known as DNS-Security or
DNSSec.
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