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I have a weird problem in that I suddenly can't monitor 5 of my nagios machines. These 5 client machines are all running RHEL 5, and are virtual machines under VMWare. They all stopped working around the same period. My /var/log/messages simply says "Cannot connect from xxx.xxx.xxx.xxx" (real IP replaced). From my nagios server, I simply get "CHECK_NRPE: Error - Could not complete SSL handshake"
I can telnet to port 5666 on the client machine from the nagios server, though it disconnects after 3-5 seconds. I've verified that 5666 is being listened for on the client machines. I've tried re-installing on the client machines, and rebooting the client servers. There weren't any changes or patching done on those servers, and the router folk and firewall people all say everything looks ok from their end. I've disabled IPtables and SELinux, but I still can't get anything from nagios. The client machines are on different VLANs in our network, and other VM machines on those networks are working correctly.
I'd love to hear from folks on ways to help diagnose the problem. I don't think it's on the clients or nagios server, and suspect it's something in the firewall or network end at our border, but I'm not sure how to proceed. Any suggestions will be greatly appreciated.
No, the server hasn't changed or had patches applied, and the versions of nagios are the same. I ran the check_nrpe on the server and still get the "CHECK_NRPE: Error - Could not complete SSL handshake." I seem to get this error when I can't connect to the client machine, such as when the nrpe.cfg isn't running on the client machine, but I've confirmed that it's running, and port 5666 is being listened for.
Telnet'ing to port 5666 gives me a "Connected to" the server message, but then breaks the connection after about 3 to 5 seconds. Telnet'ing to one of the good machines stays connected until I issue a quit command or an interrupt.