I am sorry i never meant to be offensive rather than informative.
The service check_mk_discovery is being added automatically and it keeps running even if you add an IP or a router, even a Windows client or not, until you disable this rule manually. This service is trying to reach for an agent and it throws an error.
This agent can be installed only in a small portion of the monitored devices in an infrastructure this is why i am using SNMP.
Thanks for your patience!