> According to the IP standard, they should send back an ICMP Destination Unreachable message with a code 13, "Communication administratively prohibited". Agre

> According to the IP standard, they should send back an ICMP Destination Unreachable message with a code 13, "Communication administratively prohibited". Agreed. However, I've discovered that even folks who really should know better don't know what to do with anything other that port-unreachable: In the past, I tried setting my ip[6]tables REJECT targets to send back admin-prohibit. For... reasons[0], I was REJECTing IPv6 traffic to Google's networks. I discovered that YouTube on a Nexus device running Android Jellybean would not fail over to IPv4 but would, instead, sit and spin for multiple minutes before reporting a fatal connection failure. [0] At the time I had a IPv6 tunnel that (for some reason) transferred packets destined for Google very, very slowly.