VERS, or Version. The first 4-bit field in a datagram, or IP packet header. It contains the protocol version that was used to create the datagram, and is used to verify that the sender, receiver, and any router in the middle agree on the datagram format. This field is checked by IP software before processing a datagram to ensure that the format matches on both ends. A machine will reject datagrams with a differing version from its own.