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Slow DNS Response

Reference Number: AA-02211 Views: 3368 0 Rating/ Voters

What is DNS?

Computers communication with each other over a network, or the Internet by using IP Addresses to identify the sending and receiving machines. These are typically groupings of numbers, such as 192.168.1.123, however it is more convenient for humans to use names to refer to computers, such as "lumenvox.com", since this is easier to remember.

DNS refers to the Domain Name System, which is the mechanism by which computer names (e.g. lumenvox.com) are converted into IP addresses (e.g. 192.168.1.123).

This is an vital mechanism needed to make network communications work correctly. It is also important that this lookup happens quickly, so that communication delays are not introduced.


Slow DNS Response

This warning can be generated as a result of running the LumenVox Dashboard Diagnostics and is an indication that a longer than typical response time was detected when performing DNS lookups for the specified FQDNs. This is generally an indication that DNS is not configured correctly on the server - likely associated with the primary DNS server being used.

Ideally any DNS lookup should respond very quickly (only a few milliseconds). Lengthier DNS lookups take more time to complete, which can introduce latency to network traffic, ultimately affecting overall system performance because network packets can be significantly delayed.

The DNS_WARN_THRESHOLD setting in manager.conf (also accessible via the Dashboard configuration screen for the manager) can be used to adjust the amount of time before a warning is triggered, in order to mask such problems, however lengthy DNS response times can be problematic to overall network operation, so should not be ignored.

We introduced this DNS check to our diagnostic testing in response to some production systems that were found to have incorrectly configured or incorrectly functioning DNS. These systems were suffering significant performance degradation in ASR and TTS performance, which took a long time to remedy. Ultimately, the root cause was discovered to be incorrect DNS operation on the server, and once corrected, the ASR and TTS problems went away.

Warning: 

If you receive this warning when performing diagnostics, we recommend that your network administrator should look at the server and determine why these DNS delays are happening and correct the DNS configuration to resolve this issue, since it is likely this affects all software and not just LumenVox applications.

As a temporary workaround to mitigate this issue until it can be fixed correctly, you could add name resolution entries to you system's hosts file, however you should undo these temporary entries when the DNS problem has been resolved. We do not recommend this as a long-term solution to the problem - DNS resolution should be working optimally to ensure correct operation.

You can also use IP Addresses in place of domain names, which removes the need for most DNS lookup, however some lookup may be needed for accessing external machines, such as LumenVox cloud-based servers, etc.