Jason Antonacci: Clever Guy

TL;DR Disabling IPv6 necessitates SSHd AddressFamily is "inet" for X11 Forwarding to work. Issue OpenSSH assumes both IPv6 and IPv4 protocols are enabled, and default SSHd AddressFamily value "any" is valid. Quickly skimming the OpenSSH source code, it was not obvious why SSHd does not fail gracefully, selecting only an available IP address family. Therefore, for X11 Forwarding to work correctly, in /etc/ssh/sshd_config we must choose: Defaults - IPv6 enabled and SSHd AddressFamily value " any " Custom - IPv6 disabled and SSHd AddressFamily value " inet " Background PuTTY was not creating a $HOME/.Xauthority file on ssh login and no X11 applications would run, despite setting $DISPLAY.  PuTTY was correctly configured with: X11 Forwarding enabled X display location empty Remote authentication protocol MIT-Magic-Cookie-1 X authority file for local display empty On the initial ssh login there should be a .Xauthority notic

Occasionally devices fail to respond to a ping.  This can result from devices being off-line, having a local firewall enabled or the perimeter firewall configuration.  The Cisco ASA ICMP packet-tracer options differ from the TCP or UDP command options.  An example is below: packet-tracer input outside icmp A.B.C.D 8 0 E.F.G.H The ICMP type is "8" (echo request) with code"0" (none).  There are no options on destination IPv4 address E.F.G.H. Complete ICMP documentation at URL http://www.iana.org/assignments/icmp-parameters/ Complete Cisco ASA packet-tracer documentation at URL http://www.cisco.com/en/US/docs/security/asa/asa80/command/reference/p.html#wp1878788