First, let me thank everyone who responded to my previous question about routers prioritizing control traffic, your comments were much appreciated. My next question is about responses to ICMP pings (echo request), when they return ICMP UNREACHABLE with codes 9,10 or 13. These codes are defined as follows: unreachable 9 Communication with Destination Network is Administratively Prohibited unreachable 10 Communication with Destination Host is Administratively Prohibited unreachable 13 Communication Administratively Prohibited - generated if a router cannot forward a packet due to administrative filtering Responses with these codes seem to imply the presence of a firewall. Is this assumption correct or are these codes meaningless? If this a configurable parameter, how to you typically decide what to set it to? Thanks! Christos Papadopoulos Colorado State University