3com S7906E 설치 설명서

 

1-2 

Table 1-1 Stages in session establishment and interaction between an SSH client and the server 

Version negotiation 

SSH1 and SSH2.0 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. 

After passing authentication, the client sends a session 
request to the server. 

Interaction 

After the server grants the request, the client and server start 
to communicate with each other. 

 

1)  The server opens port 22 to listen to connection requests from clients. 

2)  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.  

3)  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.  

4)  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. If the server 

supports the version, the server and client will use the version. Otherwise, the negotiation fails.  

5)  If the negotiation is successful, the server and the client proceed with key and algorithm negotiation; 

otherwise, the server breaks the TCP connection.  

 

All the packets involved in the above steps are transferred in plain text. 

 

z 

The server and the client send algorithm negotiation packets to each other, which include the 

supported public key algorithms list, encryption algorithms list, Message Authentication Code 

(MAC) algorithms list, and compression algorithms list.  

z 

Based on the received algorithm negotiation packets, the server and the client figure out the 

algorithms to be used. If the negotiation of any type of algorithm fails, the algorithm negotiation fails 

and the server tears down the connection with the client.