Why does my Unix server do so many DNS lookups?

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Question

GMS software will attempt to resolve MX records using UDP making multiple requests, each failing back a random number of seconds. If there is still no resolution, the much slower but more reliable TCP transport is used to resolve the hostname.

When a DNS server is used to look up MX records which contain a large number of entries (e.g. waitrose.com) the DNS server may receive a large number of lookup requests because:

  • It does not respond fast enough to UDP requests.
  • There is no response to the attempt to connect via TCP.

Answer

In this version of GMS, the attempt to obtain MX records via TCP failed due to an error in the socket wrapper functions.

In the vast majority of cases, this will cause no problems. However, for domains that take a long time to respond to MX records, the TCP fails and GMS retries UDP again.

The fix solves the TCP connection problem.

See Also:

Keywords:DNS lookup UNIX linux MX

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