Thnx for your reply.
Yes, it's similar. And I indeed already found a way to accomplish it with an external monitor.
However, there's 2 reasons why I still ask this question.
1) All over the internet I encounter warnings that external monitors are resource heavy. Which is logical because each time a check is fired, a bash shell is started. This goes into serious numbers when hundreds of servers have this check attached and fired regularly.
2) As far as I read the documentation correctly it says that when send and receive string are not BOTH filled in, all that is done in the (reverse) tcp check is just a connection check. And for a reverse connection check it makes no sense to go or stay down when no connection can be made. So either I am doing something wrng or this is a nasty bug, which appearantly s there for a long time already.