Add ssh config info

_episodes/11-connecting.md

@@ -65,6 +65,48 @@ Even if your cluster does not require it, the next section will guide you
 through the use of SSH keys and an SSH agent to both strengthen your security
 _and_ make it more convenient to log in to remote systems.
 
+## Setting up the ssh configuration file
+
+The Greene cluster has multiple login nodes (`log-1`, `log-2`, `log-3`) any of which
+can be assigned as the login node. This can sometimes lead to the following warning:
+```
+@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
+@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
+
+IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
+Someone could be eavesdropping on you right now (man-in-the-middle attack)!
+It is also possible that a host key has just been changed.
+```
+{: .language-bash}
+
+To avoid this error, open the file ``~/.ssh/config` on your computer  and place the
+following lines in it:
+```
+Host greene.hpc.nyu.edu dtn.hpc.nyu.edu
+  StrictHostKeyChecking no
+  ServerAliveInterval 60
+  ForwardAgent yes
+  StrictHostKeyChecking no
+  UserKnownHostsFile /dev/null
+  LogLevel ERROR
+```
+{: .language-bash}
+
+Additionally, some people may experience connection warnings while connecting to Greene,
+ and connections being terminated too soon.This can be addressed by entering the
+following into ``~/.ssh/config` file:
+```
+# Increase alive interval
+  host *.hpc.nyu.edu
+  ServerAliveInterval 60
+  ForwardAgent yes
+  StrictHostKeyChecking no
+  UserKnownHostsFile /dev/null
+  LogLevel ERROR
+```
+{: .language-bash}
+
 ## Log In to the Cluster
 
 If you are connecting from a remote location that is not on the NYU network (your home