Use um script python ou perl simples para falsificar o protocolo.
Pare seu daemon ssh no servidor e inicie o script Python:
class MyTCPHandler(SocketServer.BaseRequestHandler):
"""
The RequestHandler class for our server.
It is instantiated once per connection to the server, and must
override the handle() method to implement communication to the
client.
"""
def handle(self):
# self.request is the TCP socket connected to the client
self.data = self.request.recv(1024).strip()
print "%s wrote:" % self.client_address[0]
print self.data
# just send back the same data, but upper-cased
# Simulate error Here!
# maybe exit()
self.request.send(self.data.upper())
if __name__ == "__main__":
HOST, PORT = "localhost", 22
# Create the server, binding to localhost on port 9999
server = SocketServer.TCPServer((HOST, PORT), MyTCPHandler)
# Activate the server; this will keep running until you
# interrupt the program with Ctrl-C
server.serve_forever()
Basta ajustar o script para fazer com que ele "falhe" do jeito que você quer ou não responder, mandar lixo de volta ou matar o processo do ouvinte.