Q: All my monitored devices are DHCP based. I poll using DNS name. I am doing a simple ping to verify if they are responding or not. Last night we had a power surge or something, and all the devices grabbed new IP addresses. The next pass through, they all showed as down. It appears that when the poll cycle goes through it is looked up by IP address, not by DNS name. Based on the description of poll using DNS, I would have expected it to lookup the ip address each time it went through a poll cycle. What’s wrong?
A: Please note that, to decrease load on DNS servers, DNS requests are often cached. In such a case, the piece of software could use cached (invalid) value of DNS response.
To prevent that reliably, please stop DNS client service at the computer running IPNetwork Monitor (and set its startup option to «Manual»), and make sure that at least primary DNS server (listed to be contacted first) always returns actual response data.
Note that disabling the mentioned DNS client service could result in much more frequent requests to DNS servers.
Related topics
How to monitor network devices with dynamic IPs?
Check out our Knowledge Base where we answer questions regarding various topics. DNS answers can be cached by the operating system or resolver, so a monitor may keep using a stale address until that cached DNS entry expires or is bypassed. Stop the DNS Client service on the computer running IPNetwork Monitor, set that service to Manual, and make sure the primary DNS server returns current address data. The monitoring computer will send DNS requests more often, which can increase load on DNS servers but helps avoid stale cached responses for frequently changing DHCP devices.
Frequently Asked Questions
Why can DNS-based polling still use an old IP address?
How can IPNetwork Monitor pick up DHCP address changes more reliably?
What is the tradeoff of disabling the DNS Client service?