H3C Technologies H3C WX3000E Series Wireless Switches - Manual (Page 302)

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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 access controller 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 access controller supports SSH2.0 and SSH1. When
acting as an SSH client, the access controller supports SSH2.0 only.
Unless otherwise noted, SSH in this document refers to SSH2.0.
How does SSH work
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 13 .
Table 13 Stages in session establishment and interaction between an SSH client and the server
Stages Description
Version negotiation
SSH1 and SSH2.0 are supported. The two parties negotiate a version to
use.
Key and algorithm negotiation
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.
Authentication
The SSH server authenticates the client in response to the client's
authentication request.
Session request
After passing authentication, the client sends a session request to the
server.
Interaction
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-
number>.-. 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