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--- computing:linux:ssh [2011/12/16 11:04]
gcooper created
+++ computing:linux:ssh [2018/01/15 11:57] (current)
gcooper
@@ Line 1: / Line 1: @@
 ====== SSH ======
-===== Set Up SSH Keys =====
+See also **[[computing:linux:ssh_keys|Set Up SSH Keys]]**
-See [[computing:linux:ssh_keys|Set Up SSH Keys]].
 ===== Troubleshooting =====
+Verbose:
 <file>
 ssh -v ...
+</file>
+Modify the MTU on your remote workstation PC to eliminate fragmentation (MTU mismatch):
+<file>
+ifconfig eth0 mtu 576
 </file>
@@ Line 28: / Line 34: @@
 <file>
-chmod 600 /home/gcooper/.ssh/config
+chmod 600 /home/username/.ssh/config
+</file>
+==== Unknown Terminal Type ====
+If you get an error message "unknown terminal type", you can try specifying a different terminal like this:
+<file>
+TERM=xterm-color ssh -l username remote.host.name
 </file>
@@ Line 42: / Line 56: @@
 service sshd restart
 </file>
+==== Additional for EL7 ====
+Install ''semanage'' if it is not installed and allow ssh on your port:
+<file>
+sudo yum install policycoreutils-python
+semanage port -a -t ssh_port_t -p tcp 2222
+</file>
+===== Reverse Tunnels =====
+http://www.howtoforge.com/reverse-ssh-tunneling
+http://www.alexonlinux.com/reverse-ssh-tunnel-or-connecting-to-computer-behind-nat-router
+This technique is used to access an SSH host behind a NAT firewall using a middle-man PC with a static IP address.
+  * Box behind NAT creates a reverse tunnel connection to the middle-man
+  * User connects to middleman PC on reverse tunnel port
+==== Howto ====
+On the middle-man host with a real static IP address:
+  * Set "GatewayPorts yes" in /etc/ssh/sshd_config
+    * Restart sshd if sshd_config changed
+  * Configure to use [[computing:linux:ssh_keys|SSH keys]] rather than passwords
+    * Less trouble
+    * More secure
+On remote host (behind NAT) that you want to access:
+<file>
+ssh -R 22222:localhost:22 root@middleman
+</file>
+or if SSH is listening on a non-standard port:
+<file>
+ssh -R 22222:localhost:22 root@middleman -p 2222
+</file>
+From your workstation, connect through the middle-man PC:
+<file>
+ssh -p 22222 root@middleman
+</file>
+===== AutoSSH =====
+http://www.howtoforge.com/reverse-ssh-tunneling#comment-4762
+Use AutoSSH to keep a tunnel up constantly.

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