Both the Zenoss Core server and the monitored devices have port requirements. The Zenoss Core server needs to allow access to the following ports:
To facilitate monitoring, the systems on the network need to allow access to the following ports:
UDP 161 for SNMP requests
TCP port 22 for remote collector plugins via SSH
TCP port 23 for remote collector plugins via Telnet
This is a common list of ports, but network and monitoring needs are unique from one site to the next. For example, if you do not plan to monitor any devices with the Zenoss Plugins over Telnet, then don't open port 23 on your monitored devices.