This memo specifies the Simple Middlebox Configuration (SIMCO) protocol for configuring Network Address Translators (NATs) and firewalls dynamically to create address bindings and open pinholes. NATs and firewalls are a problem for applications using voice and video streaming, such as IP telephony, because they need to establish voice or video channels dynamically. The SIMCO protocol allows clients to send requests for this purpose to serving NATs and/or firewalls. The protocol is designed to provide a simple and basic solution that can easily be implemented and used. The protocol meets all requirements defined by the MIDCOM working group (see [4]) and it implements the MIDCOM semantics [3].