Which field defines the length of the IP header and any valid data (although it does not include any data link padding) ?

Total length.

Explanation:

In computer networking, network models are used to define the communication between computers. The OSI and the TCP/IP suite model are examples of this network models. The OSI has seven layers while TCP/IP has four defined layers.

Each layer of the models defines a protocol datagram unit or PDU, which is created by encapsulating the data from the previous layer with the header of the current one.

For example, the network layer of the OSI model which is equivalent to the internet layer of the TCP/IP suite encapsulates data with the IP header to form the packet. The length of the header is the total length of the defined packet.