unicast and anycast speed comparison

Advocates of anycast dns services claim that anycast dns is inherently faster than unicast dns. These claims are often made as self-evident fact without further substantiation.

However, it is possible to test this claim using publically available tools from independent sources.

just-dnslookup.com is a site that times dns lookups from 59 globally dispersed data centers as of the time of this test.

intodns.com was used to verify the published authoritative name servers for each domain.

The tests were performed for a domain using anycast dns and a domain using unicast dns. The results show that not only is unicast competitive with anycast, it is often faster. The claim that anycast is inherently faster than unicast is simply not viable in the light of these test results.

COMBINED TEST RESULT, 2011-07-27

The composite screenshot to the right shows the dns query times from both anycast and unicast lookups for two A records. It has been created by combining parts of the two screenshots in the following sections. This has been created solely for ease of viewing on a single page. The composite data remains the same as the source data.

The icon colors appear to have the following meanings:

green	0-500 ms.
yellow	500-1000 ms.
red	1000+ ms.

click thumbnail images to view full size

ANYCAST TEST RESULT, 2011-07-27 06:10 GMT (dnsmadeeasy)

UNICAST TEST RESULT, 2011-07-27 06:18 GMT (edgedirector)

A note of caution for those wishing to try to duplicate the results is in order. The dns servers used by just-dnslookup.com appear to respect the TTL sent by the authoritative dns servers. If a test is repeated before the TTL has expired, the lookup result is the time taken to retrieve the result from cache. If this happens, the tester must wait until the TTL has expired before trying the test again.