The version number field in the header is bits long, the datagram length field is bits long.

It seems you're interested in the length of certain fields in a datagram header, likely in the context of networking protocols, specifically IP (Internet Protocol). To answer your question:

In the IPv4 header:

1. The Version Number field is 4 bits long. This field indicates the version of the IP protocol being used (e.g., IPv4 or IPv6).
2. The Datagram Length field, which is called the Total Length field in the IPv4 header, is 16 bits long. This field specifies the total length of the IP packet, including the header and the data.

This clear delineation of the lengths of each of these fields highlights the importance of header information in networking, as it dictates how routers and devices interpret incoming packets. Understanding these bit lengths is essential for network programming, protocol analysis, and system design within the realm of computer networking.