How long should I expect a reverse lookup take? 100 milliseconds? 1 second? 10 second? 30 seconds? What's your experience?
Why? We're debating adding a feature to our server software which would require a reverse DNS lookup each time a client connects. The lookup would be done synchronously, so I'm worried that it could slow connection-times down a lot. I just wanted to hear other people's experience regarding reverse DNS lookup times.
As long as it takes. A LOT depends on * Where the DNS Server is that you talk to * Whether the DNS server has the value already cached * Whether ther everse mapping mas to a proper DNS server that is also operational (or the retrieval times out).
In general, for end users, you can expect easily 200ms - the user may be at the other side of the world. I would actually assume anything up to 2minutes to be possible in case of DNS reachability issues.
Within a lan, you should normally have an answer within milliseconds. Two digit, maximum (10ms or so).
In general, synchroneous may be a REALLY bad idea here - but a lot depends on what the application actually DOES.