Ssh: ProxyCommand forward host lookup fails

PROXYsshssh-tunnel

I am trying to do an ssh multihop from my local machine to a server called cluster, using a server called merlot in-between. As per http://sshmenu.sourceforge.net/articles/transparent-mulithop.html, this is how I've made my ~/.ssh/config :

Host merlot
  HostName merlot.stat.uconn.edu
  User vdeshpande
Host cluster
  HostName stats.phys.uconn.edu
  User vdeshpande
  ProxyCommand ssh -q merlot nc -q0 cluster 22

When I type ssh cluster into the terminal, I am prompted for the password of merlot. After I enter it, I get this error:

cluster: forward host lookup failed: Unknown host
ssh_exchange_identification: Connection closed by remote host

How do I fix this? I've checked that nc is installed. Also, I can ssh into merlot and then ssh into cluster.

Best Answer

You have the ProxyCommand wrong. There are two ways how to handle it:

Preffered way is using openssh native switch -w:

ProxyCommand ssh -W %h:%p proxy

The netcat version looks this way:

ProxyCommand ssh -q proxy nc %h %p

You can't use your aliases in the remote netcat command, because it doesn't know them. Great guide are substitutions %h, which is the HostName you specified above.

So for you case:

ProxyCommand ssh -q merlot nc -q0 %h 22

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SSH – How to Recover from ‘Too Many Authentication Failures for User Root’

Are you sure that root login to ssh is allowed?

Check sshd_config and verify that root login is permitted. sshd will need to be restarted if the setting changes.

Ssh – How to automate SSH login with password

Don't use a password. Generate a passphrase-less SSH key and push it to your VM.

If you already have an SSH key, you can skip this step… Just hit Enter for the key and both passphrases:

$ ssh-keygen -t rsa -b 2048
Generating public/private rsa key pair.
Enter file in which to save the key (/home/username/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/username/.ssh/id_rsa.
Your public key has been saved in /home/username/.ssh/id_rsa.pub.

Copy your keys to the target server:

$ ssh-copy-id id@server
id@server's password:

Now try logging into the machine, with ssh 'id@server', and check-in:

.ssh/authorized_keys

Note: If you don't have .ssh dir and authorized_keys file, you need to create it first

to make sure we haven’t added extra keys that you weren’t expecting.

Finally, check to log in…

$ ssh id@server

id@server:~$

You may also want to look into using ssh-agent if you want to try keeping your keys protected with a passphrase.

Best Answer

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SSH – How to Recover from ‘Too Many Authentication Failures for User Root’

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