SSH Terminal Services
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Chapter 25. SSH Terminal Services
25.1 Introduction to SSH
Secure Shell (SSH) can provide information security and powerful authentication to
prevent such assaults as IP address spoofing, plain-text password interception when users
log on to the Switch remotely through an insecure network environment.
SSH can take the place of the Telnet to provide safe management and configuration.
A Switch can connect to multiple SSH clients, and currently supports SSHv2.0 version.
The communication process between the server and client includes these five stages:
Version negotiation stage: These operations are completed at this stage:
The client sends TCP connection requirement to the server.
When TCP connection is established, both ends begin to negotiate the SSH version.
If they can work together in harmony, they enter the key algorithm negotiation stage.
Otherwise the server clears the TCP connection.
Key algorithm negotiation stage. These operations are completed at this stage:
The server sends the public key in a randomly generated RSA key pair to the client.
The client figures out session key based on the public key from the server and the random
number generated locally.
The client encrypts the random number with the public key from the server and sends the
result back to the server.
The server then decrypts the received data with the server private key to get the client
random number.
The server then uses the same algorithm to work out the session key based on server
public key and the returned random number.
Then both ends get the same session key without data transfer over the network, while the
key is used at both ends for encryption and decryption.
Authentication method negotiation stage: These operations are completed at this stage:
The client sends its username information to the server.
The server authenticates the username information from the client.
The client authenticates information from the user at the server till the authentication
succeeds or the connection is turned off due to authentication timeout.
Session request stage: The client sends session request messages to the server which
processes the request messages.
Interactive session stage: Both ends exchange data till the session ends
