having been authorized for network access. Encryption and per-user rules that disallow users exchanging ICMP packets (and all other types of packets, maybe by using IEEE 802.1X) with external peers before authorization solves this problem. See also ICMPv6 Smurf attack References External links , Internet Control Message Protocol itun Simple IP over ICMP tunnel Hans ICMP tunnel for Linux (server and client) and BSD MacOSX (client only) ICMP-Shell a telnet-like protocol using only ICMP PingTunnel Tunnel TCP over ICMP ICMP Crafting by Stuart Thomas Using the ICMP tunneling tool Ping Tunnel Project Loki Article on ping tunneling in Phrack ICMP tunnel with C# source code icmptunnel IP over ICMP tunnel by Dhaval Kapil Tunneling protocols Internet privacy