This string sets the S/Key password the switch uses to authenticate with its Backup firewall manager, and like the primary password it always reads back as an empty octet string. Admins set this shared secret alongside xylanFwBackupAddr so the switch can fail over to the backup manager for firewall authentication without exposing the credential to later SNMP reads. For example, after configuring a new backup manager at a different IP, an admin would also SET xylanFwBackupPassword to match the shared secret configured on that backup manager.