ZyXEL Communications Dimension GS-3012, User Manual, Page: 170 / 259

GS-3012/GS-3012F User’s Guide
24-6 Access Control
24.4 SSH Overview
Unlike Telnet or FTP, which transmit data in clear text, SSH (Secure Shell) is a secure communication protocol that
combines authentication and data encryption to provide secure encrypted communication between two hosts over
an unsecured network.
Figure 24-6 SSH Communication Example
24.5 How SSH works
The following table summarizes how a secure connection is established between two remote hosts.
1. Host Identification
The SSH client sends a connection request to the SSH
server. The server identifies itself with a host key. The client
encrypts a randomly generated session key with the host key
and server key and sends the result back to the server.
The client automatically saves any new server public keys. In
subsequent connections, the server public key is checked
against the saved version on the client computer.
2. Encryption Method
Once the identification is verified, both the client and server
must agree on the type of encryption method to use.
Figure 24-7How SSH Works
3. Authentication and Data Transmission
After the identification is verified and data encryption
activated, a secure tunnel is established between the client
and the server. The client then sends its authentication
information (user name and password) to the server to log in
to the server.
24.6 SSH Implementation
Your switch supports SSH versions 1 and 2 using RSA and DSA authentication and five encryption methods (AES,
3DES, RC4, Blowfish and CAST). The SSH server is implemented on the switch for remote SMT management and
file transfer on port 22 (by default). Up to four SSH connections are allowed at a time.
24.6.1 Requirements for Using SSH
You must install an SSH client program on a client computer (Windows or Linux operating system) that is used to
connect to the switch over SSH.