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74 Chapter4·SSHFeatures Table 4.2 SSH CONNECT Protocol Message Types and Descriptions Message Number 80 81 82 90 91 92 93 94 95 96 97 98 99 100 Name SSH_MSG_GLOBAL_REQUEST SSH_MSG_REQUEST_SUCCESS SSH_MSG_REQUEST_FAILURE SSH_MSG_CHANNEL_OPEN SSH_MSG_CHANNEL_OPEN_ CONFIRM SSH_MSG_CHANNEL_OPEN_ FAILURE SSH_MSG_CHANNEL_WINDOW_ ADJUST SSH_MSG_CHANNEL_DATA SSH_MSG_CHANNEL_EXTENDED_ DATA SSH_MSG_CHANNEL_EOF SSH_MSG_CHANNEL_CLOSE SSH_MSG_CHANNEL_REQUEST SSH_MSG_CHANNEL_SUCCESS SSH_MSG_CHANNEL_FAILURE Reason Global message request Message successful Message failed Open a new channel Channel open successful Chanel open failed Flow control open Data packet Extended character data End of file packet Close specific channel Channel specific request Channel request successful Channel request failure The above messages are included in the current standard SSHv2 and may be revised as the standard is updated. The flow of the data in these three TCP protocol layers are used to establish the connectivity between the SSH server and the SSH Client. Having looked at the messages sent in the three different protocols we can now look at a diagram of how SSH establishes its primary connectivity. You can use a program like WiresharkTM to view the negotiation of the SSH session. The first and second steps are the clear text negotiation of the encryption protocols available from the client and server. Once the negotiation is complete the next steps are to create the diffie-hellman key exchange from client and server. Once these steps have occurred the rest of the data is encrypted.