NETCONF devices configured but unreachable may cause performance issues in other connected NETCONF sessions or even cause disconnection of the sessions.

AsyncSshHandler has a blocking call to verify SSH session connection and this means that the thread is occupied for the timeout period if the device is unreachable. The default values of between-attempts-timeout-millis and connection-timeout-millis are 2000 (2 seconds) and 20000 (20 seconds), respectively, so assuming sleep-factor is 1.0 (the interval between connection attempts stays the same), a single unreachable device can take up about 0.9 CPU core. So a relatively small number of unreachable devices can easily overwhelm the whole thread pool available to all the NETCONF sessions and even the NETCONF sessions without such connectivity issue can experience performance issue - long latency in the RPC response and in some cases it may be hard to maintain connectivity depending on the keepalive settings in the device.