I am connected using Tectia Client on Windows to a remote server. How can I tell if the server is running Tectia or OpenSSH, and which is being used for the current connection?

Use the statistics escape sequence

Once you are logged on to the remote server, on the terminal run this command:

~s

Note that you need to press space after the ~ character (to invoke the escape sequence) and this needs to be the first character after a newline (pressing backspace and trying again will not work)

This will show you something like this:

destination: joe@foobar:22
local host: joesmachine.com
remote version: SSH-2.0-6.0.2.84 SSH Tectia Server
local version: SSH-2.0-6.1.0.615 SSH Secure Shell
bytes in: 530
bytes out: 1
key exchanges: 1
....

Typing the escape sequence ~? will show you a list of available escape sequences:

sshg3: SSH Tectia Client 6.1.0 on x86_64-unknown-linux-gnu
Build: 615
Product: SSH Tectia Client
License type: commercial
  Supported escape sequences:
  ~.  - terminate connection
  ~^Z - suspend ssh
  ~#  - list forwarded connections
  ~-  - disable escape character uncancellably
  ~?  - this message
  ~~  - send the escape character by typing it twice
  ~V   - dump version information to stderr
  ~s   - dump statistics and connection information to stderr
  ~c   - dump statistics and information about individual channels
  ~r   - initiate rekey immediately with old algorithms (ie. changes
         encryption and integrity keys)
  ~l   - go to line mode (keystrokes are gathered to an internal
         buffer, and will be output all at once when you enter
         a newline)
  (Note that escapes are only recognized immediately after newline.)

Use telnet

Another way to see what is running on the server side is running the telnet command to port 22 for the particular server such as:

 telnet server.com 22

This will output something like this (if an SSH server is running on that port):

Trying 1.2.3.4...
Connected to server.com.
Escape character is '^]'.
SSH-2.0-6.0.2.84 SSH Tectia Server

Use

 
    % ssh-broker-ctl lc  
    1. example.org port 22 as joe [#408]  
       Open since Tue Oct 13 11:36:12 2009 [up 7 days 02:17:42]  
       3 open channels.

to list your connection, find your connection to the specified host and use

 
    % ssh-broker-ctl cs 408  
    example.org port 22 as joe [#408]  
    Server version: SSH-2.0-6.1.0.668 SSH Tectia Server  
    Open since Tue Oct 13 11:36:12 2009 [up 7 days 02:17:49]  
     ...