How can I find current SSH protocol version of the current connection?
I connect to a Linux machine (CentOS 6.4) using PuTTY. Except from fact that I can set PuTTY to only use one type of protocol, how can I find the current SSH connection's version (SSH1 or SSH2)?
Once you are in you say:
ssh -v localhost
it will tell you the exact version of the server.
An alternative way.
As cstamas suggested, you can use ssh -v localhost. Uou simply ssh to yourself 127.0.0.1 on verbose mode, which will display debugging messages of the progress. Yes, through this process you can look at the top of the communication and you can get the SSH version that you are currently running.
But if you read the ssh man page, you will find the -V option on ssh more useful. Taken out the ssh man page:
-V Display the version number and exit.
-v Verbose mode. Causes ssh to print debugging messages about its progress. This is helpful in debugging connection, authentication, and configuration problems. Multiple -v options increase the verbosity. The maximum is 3.
So I think it would be better to simply do ssh -V and get something similar to:
> ssh -V
OpenSSH_6.6.1p1, OpenSSL 1.0.1e-fips 11 Feb 2013
PuTTY
In Session, Logging, select the "SSH packets and raw data" radio button. Select the log file as putty.log in a location of your choice. Make the connection. You should see:
Event Log: Server version: SSH-2.0-OpenSSH_5.3
Event Log: Using SSH protocol version 2
See below for details on what SSH-2.0 means.
Other Methods
You could also try using the telnet client, but point to port 22:
telnet test1 22
When you connect you will see:
Trying 192.168.144.145...
Connected to test1.
Escape character is '^]'.
SSH-2.0-OpenSSH_5.3
The last line is the one to look for:
SSH-2.0-OpenSSH_5.3
If it says SSH-2.0 then that is good, the SSH server you connected to supports only SSH protocol version 2. It will not support connections from SSH V1 protocol clients.
If however you see:
SSH-1.99-OpenSSH_5.3
Then that means that the server end is still supporting SSH protocol version 1. It has something like this in it's sshd_config file:
Protocol 1,2
Protocol 1 is vulnerable and should not be used.
So to get that straight. If you see SSH-2 when you telnet to port 22 of the remote server then you can only be using SSH protocol version 2 as the server does not support protocol 1.
As per cstamas answer above, the -v flag will show a line:
debug1: Remote protocol version 1.99, remote software version OpenSSH_5.3
or:
debug1: Remote protocol version 2.0, remote software version OpenSSH_5.3
You want to see version 2.0 there.