3com 5500-ei pwr Installation Instruction

 

1-3 

Data exchange 

The client and the server start to communicate with each 
other. 

 

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Currently, the switch that serves as an SSH server supports two SSH versions: SSH2 and SSH1, 

and the switch that serves as an SSH client supports only SSH2.  

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Unless otherwise noted, SSH refers to SSH2 throughout this document. 

 

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

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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.  

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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.  

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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.  

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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. 

 

All the packets above are transferred in plain text. 

 

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

key algorithm lists supported by the server and the client, encrypted algorithm list, message 

authentication code (MAC) algorithm list, and compressed algorithm list.  

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The server and the client calculate the final algorithm according to the algorithm lists supported.  

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The server and the client generate the session key and session ID based on the Diffie-Hellman 

(DH) exchange algorithm and the host key pair.  

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Then, the server and the client get the same session key and use it for data encryption and 

decryption to secure data communication.