Typically for a device we use show version to view the serial number. However, for some strange reason, in the ASA-X the number that is listed in the show version is not actually the serial number. If you try and open a TAC case that serial does not show up in TAC’s database. There is a parent serial number which you must provide. That number can be found with a show inventory.
ASA-CX#show version ... ... Intercompany Media Engine : Disabled perpetual IPS Module : Disabled perpetual Cluster : Disabled perpetual This platform has an ASA5525 VPN Premium license. Serial Number: FCH1710**** ASA-CX#show inventory Name: "Chassis", DESCR: "ASA 5525-X with SW, 8 GE Data, 1 GE Mgmt, AC" PID: ASA5525 , VID: V01 , SN: FGL1711****
The serial number you would use to open a TAC case in this example would be FGL1711****