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The ICSI Netalyzr Start » Analysis » Results DNS CNAMEs

About this test: In order to translate a mnemonic name (such as "netalyzr.icsi.berkeley.edu") to an IP address, your computer contacts a Domain Name Service (DNS) resolver. This is a computer controlled by your ISP which acts as an intermediary.

One portion of how DNS resolvers operate is how they respond to CNAMEs. When your ISP's resolver asks for a name like "www.google.com", the response can include a CNAME saying "www.google.com is really www.l.google.com". Additionally, the response can, at the same time, include a record for the alias, giving the address for "www.l.google.com".

An important but subtle portion of DNS operations is how your ISP's DNS resolver accepts these fields, as part of the "glue acceptance" or "bailiwick checking" policy.

This test works by querying special names in a domain we control, where the response is different depending on whether the additional data for the CNAME is accepted or not. Thus we can deduce how the DNS resolver handles CNAMEs.

For additional information on the results, please consult the Netalyzr help site over at the New Scientist. Close window

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