On 31.03.21 10:56, Tom Preissler via bind-users wrote:
at my work place we have a three resolver setup in /etc/resolv.conf.
resolv.conf is not a BIND thing, it's configuration of system libraries.
We had sometimes, though rarely, response times for DNS like 14000ms, due to the fact that the *first* listed resolver is down for maintenance reasons. The application we test this with is Oracle/TNSPing.
if this is an issue, you can run local caching DNS server like BIND or dnsmasq. They can handle such timeouts better than most libraries.
As a mitigation we therefore put in timeout:1, but we just recently got again a TNSPing response of 9000ms. I noticed in man resolv.conf this section on "timeout": timeout:n Sets the amount of time the resolver will wait for a response from a remote name server before retrying the query via a different name server. | This may not be the total time taken by any | resolver API call and there is no guarantee that a | single resolver API call maps to a single timeout. Measured in seconds, the default is RES_TIMEOUT (currently 5, see <resolv.h>). The value for this option is silently capped to 30. I am intrigued by the above sentence marked with "|". Does anybody know what that means in detail, can anybody explain that please? I explained the reason for the 9000ms so that Oracle and its many processes all come together to resolve the DNS name and they *keep hitting* the first resolver - and "timeout" can't kick in due to parallel requests from different processes, hence the high overall response time.
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