Some IPv4 features.

Version ID, 4 bit field (IPv4=4 or IPv6)

Total length of packet - minimum of 20 bytes, max of 65535

Source and destination IP identifiers, 4 octet value.

TTL - time to live. Because the Internet provides multiple paths to a destination, it is possible for a packet to get lost. The TTL field is used to count, by decrementing, the number of times a packet is transferred between nodes. If the count reaches zero, the packet is assumed to be lost and is destroyed.

Packet fragmentation - historically new nodes/links were added to the Internet in an adhoc manor. The frame size of these varied based on the specific protocol of the network. IPv4 allows an IP packet to be fragmented in order to move over a network/link which supports a smaller packet than original packet/frame.