Description: This object represents the vendor-specific second serial number string for the physical entity. The first serial number string of the physical entity is represented in the value of corresponding instance of the 'entPhysicalSerialNum' object.

On the first instantiation of an physical entity, the value of this object is the correct vendor-assigned second serial number, if this information is available to the agent.

If the second serial number is unknown or non-existent, then the value of this object will be a zero-length string instead.

Note that implementations which can correctly identify the second serial numbers of all installed physical entities do not need to provide write access to this object. Agents which cannot provide non-volatile storage for the second serial number strings are not required to implement write access for this object.

Not every physical component will have a serial number, or even need one. Physical entities for which the associated value of the entPhysicalIsFRU object is equal to 'false(2)' (e.g., the repeater ports within a repeater module), do not need their own unique serial number. An agent does not have to provide write access for such entities, and may return a zero-length string.

If write access is implemented for an instance of 'ceEntPhysicalSecondSerialNum', and a value is written into the instance, the agent must retain the supplied value in the 'ceEntPhysicalSecondSerialNum' instance associated with the same physical entity for as long as that entity remains instantiated. This includes instantiations across all re- initializations/reboots of the network management system, including those which result in a change of the physical entity's entPhysicalIndex value.