Oliver, I am trying to accomplish the same thing with threads as Miky moving from Net::Telnet::Cisco. I can fall back to fork() if I have to, but somehow Net::Telnet::Cisco avoids this issue with threads. I have run in to a signaling issue on timeouts connecting to a host using Net::Telnet that will kill off my threads, so likely it is not fully thread-safe. It was related to $SIG{ALRM}. Perhaps your method for timeout on prompt is running in to a similar issue. I have to say I'm no expert on this, but somehow Net::Telnet::Cisco avoids the issue with threads. Other than that it looks like a great library that I can use in other areas that don't require parallel jobs. Thanks