Ssh Operating Process - H3C S5600 Series Operation Manual

Operation Manual – SSH
H3C S5600 Series Ethernet Switches
Note:
Currently, SSH supports both RSA and DSA.

1.1.4 SSH Operating Process

The session establishment between an SSH client and the SSH server involves the
following five stages:
Table 1-1 Stages in establishing a session between the SSH client and server
Version negotiation
Key and algorithm negotiation
Authentication
Session request
Data exchange
I. Version negotiation
The server opens port 22 to listen to connection requests from clients.
The client sends a TCP connection request to the server. After the TCP
connection is established, the server sends the first packet to the client, which
includes a version identification string in the format of "SSH-<primary protocol
version number>.<secondary protocol version number>-<software version
number>". The primary and secondary protocol version numbers constitute the
protocol version number, while the software version number is used for
debugging.
The client receives and resolves the packet. If the protocol version of the server is
lower but supportable, the client uses the protocol version of the server; otherwise,
the client uses its own protocol version.
The client sends to the server a packet that contains the number of the protocol
version it decides to use. The server compares the version carried in the packet
with that of its own to determine whether it can cooperate with the client.
If the negotiation is successful, the server and the client go on to the key and
algorithm negotiation. If not, the server breaks the TCP connection.
Stages
1-3
Description
SSH1 and SSH2 are supported. The two parties
negotiate a version to use.
SSH supports multiple algorithms. The two
parties negotiate an algorithm for
communication.
The SSH server authenticates the client in
response to the client's authentication request.
This client sends a session request to the server.
The client and the server start to communicate
with each other.
Chapter 1 SSH Configuration