HP 6125G HP 6125G & 6125G/XG Blade Switches Security Configuration Gui - Page 187
Configuring SSH2.0, Overview, SSH operation, Version negotiation
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Configuring SSH2.0 Overview Secure Shell (SSH) offers an approach to logging in to a remote device securely. Using encryption and strong authentication, SSH protects devices against attacks such as IP spoofing and plain text password interception. The switch can not only work as an SSH server to support connections with SSH clients, but also work as an SSH client to allow users to establish SSH connections with a remote device acting as the SSH server. When acting as an SSH server, the switch supports SSH2.0 and SSH1. When acting as an SSH client, the switch supports SSH2.0 only. Unless otherwise noted, SSH in this document refers to SSH2.0. SSH operation To establish an SSH connection and communicate with each other through the connection, an SSH client and the SSH server go through the stages listed in Table 11. Table 11 Stages in session establishment and interaction between an SSH client and the server Stages Version negotiation Key and algorithm negotiation Authentication Session request Interaction Description SSH1 and SSH2.0 are supported. The two parties negotiate a version to use. SSH supports multiple algorithms. The two parties negotiate algorithms for communication, and use the DH key exchange algorithm to generate the same session key and session ID. The SSH server authenticates the client in response to the client's authentication request. After passing authentication, the client sends a session request to the server. After the server grants the request, the client and the server start to communicate with each other. Version negotiation 1. The server opens port 22 to listen to connection requests from clients. 2. The client sends a TCP connection request to the server. 3. After the TCP connection is established, the server sends a packet that carries a version information string to the client. The version information string is in the format SSH-.-. The primary and secondary protocol version numbers constitute the protocol version number. The software version number is used for debugging. 4. After receiving the packet, the client resolves the packet and compares the server's protocol version number with that of its own. If the server's protocol version is lower and supportable, the client uses the protocol version of the server; otherwise, the client uses its own protocol version. In 177