Could a packet with all 0s or all 1s be a legal IPv4 packet?

Yes, a packet with all 0s or all 1s can technically be a legal IPv4 packet, as long as it adheres to the IPv4 header format and other protocol specifications. However, an all-0s packet may be considered invalid in practical scenariOS since it would likely represent an undefined or non-routable address. An all-1s packet, often representing a broadcast address, could be valid in certain contexts, such as for broadcasting messages to all devices on a local network.