H3C Technologies H3C S12500-X Series Switches - Manual (Page 181)

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Configuring SSH
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Overview
Secure Shell (SSH) is a network security protocol. Using encryption and authentication, SSH can
implement secure remote access and file transfer over an insecure network. Adopting the typical
client/server model, SSH can establish a channel to protect data transfer based on TCP.
SSH includes two versions: SSH1.x and SSH2.0 (hereinafter referred to as SSH1 and SSH2), which are
not compatible. SSH2 is better than SSH1 in performance and security.
The device can work as an SSH server to provide services to SSH clients, and can work as an SSH client
to allow users to establish SSH connections with a remote SSH server. When acting as an SSH server, the
device supports SSH2 and SSH1 in non-FIPS mode and supports only SSH2 in FIPS mode. When acting
as an SSH client, the device supports SSH2 only.
The device supports the following SSH applications:
• Secure Telnet—Stelnet provides secure and reliable network terminal access services. Through
Stelnet, a user can securely log in to a remote server. Stelnet can protect devices against attacks,
such as IP spoofing and plain text password interception. The device can act as an Stelnet server or
an Stelnet client.
• Secure File Transfer Protocol—SFTP, based on SSH2, uses SSH connections to provide secure file
transfer. The device can serve as an SFTP server, allowing a remote user to log in to the SFTP server
for secure file management and transfer. The device can also serve as an SFTP client, enabling a
user to log in from the device to a remote device for secure file transfer.
• SCP—Based on SSH2, SCP offers a secure approach to copying files. The device can act as an SCP
server, allowing a user to log in to the device for file upload and download. The device can also act
as an SCP client, enabling a user to log in from the device to a remote device for secure file transfer.
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How SSH works
This section uses SSH2 as an example to list the stages involved in secure session establishment between
an SSH client and an SSH server. For more information about these stages, see SSH Technology White
Paper.
Table 10 Stages involved in secure session establishment
Stages Description
Connection establishment
The SSH server listens to the connection requests on port 22. After a
client initiates a connection request, the server and the client establish a
TCP connection.
Version negotiation The two parties determine a version to use after negotiation.
Algorithm negotiation
SSH supports multiple algorithms. Based on the local algorithms, the two
parties determine the key exchange algorithm for generating session
keys, the encryption algorithm for encrypting data, the public key
algorithm for digital signature and authentication, and the HMAC
algorithm for protecting data integrity.