Dear Nanogers, We are a bunch of academic researchers interested in Internet security. We notice that some research papers require that BGP router clocks be globally synchronized to a 5-minute granularity. If a router's clock is off by more than 5 minutes, it cannot forward packets, but there's no other side effect. From an operational point of view, do you think it is a practical requirement? If not, what are the potential problems that prevent router clocks from being loosely synchronized? If you consider 5-minute too small, what do you consider as a practical clock skew requirement for BGP routers on the Internet? We'd appreciate your input very much. It will help us understand what's practical and what's not in our work. Please reply to us directly. Thanks, Xin Liu