SSH client contact behavior

At the first contact between the switch and an SSH client, if the switch public key has not been copied into the client, then the client's first connection to the switch will question the connection and, for security reasons, provide the option of accepting or refusing. If it is safe to assume that an unauthorized device is not using the switch IP address in an attempt to gain access to the client's data or network, the connection can be accepted. (As a more secure alternative, the client can be directly connected to the switch serial port to download the switch public key into the client.)

When an SSH client connects to the switch for the first time, it is possible for a "man-in-the-middle" attack; that is, for an unauthorized device to pose undetected as the switch, and learn the usernames and passwords controlling access to the switch. This possibility can be removed by directly connecting the management station to the switch serial port, using a show command to display the switch public key, and copying the key from the display into a file. This requires a knowledge of where the client stores public keys, plus the knowledge of what key editing and file format might be required by the client application. However, if the first contact attempt between a client and the switch does not pose a security problem, this is unnecessary.