Configuration Guide Configuring SSH
To ensure secure communication, interaction between an SSH server and an SSH client undergoes the following seven
stages:
Connection setup
The server listens on Port 22 to the connection request from the client. After originating a socket initial connection request,
the client sets up a TCP socket connection with the server.
Version negotiation
If the connection is set up successfully, the server sends a version negotiation packet to the client. On receiving the packet,
the client analyzes the packet and returns a selected protocol version to the server. The server analyzes the received
information to determine whether version negotiation is successful.
Key exchange and algorithm negotiation
If version negotiation is successful, key exchange and the algorithm negotiation are performed. The server and the client
exchange the algorithm negotiation packet with each other, and determine the final algorithm based on their capacity. In
addition, the server and the client work together to generate a session key and a session ID according to the key exchange
algorithm and host key, which will be applied to subsequent user authentication, data encryption, and data decryption.
User authentication
After the encrypted channel is set up, the client sends an authentication request to the server. The server repeatedly
conducts authentication for the client until the authentication succeeds or the server shuts down the connection because the
maximum number of authentication attempts is reached.
Session request
After the successful authentication, the client sends a session request to the server. The server waits and processes the
client request. After the session request is successfully processed, SSH enters the session interaction stage.
Session interaction
After the session request is successfully processed, SSH enters the session interaction stage. Encrypted data can be
transmitted and processed in both directions. The client sends a command to be executed to the client. The server decrypts,
analyzes, and processes the received command, and then sends the encrypted execution result to the client. The client
decrypts the execution result.
Session ending
When the interaction between the server and the client is terminated, the socket connection disconnects, and the session
ends.
Overview
Enable the SSH server function on a network device, and you can set up a secure connection with
the network device through the SSH client.
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