Allied Telesis AT-S63 - Manual (Page 487)

AT-S63 Management Software Features Guide
Section IX: Management Security 487
SSH Configuration Guidelines
Here are the guidelines to configuring SSH:
 SSH requires two encryption key pairs. One key pair functions as the
host key and the other as the server key.
 The two encryption key pairs must be of different lengths of at least
one increment (256 bits) apart. The recommended bit size for a server
key is 768 bits. The recommended size for the host key is 1024 bits.
 You activate and configure SSH on the master switch of an enhanced
stack, not on slave switches.
 The AT-S63 software uses well-known port 22 as the SSH default port.