Is ip datagram a fixed length datagram?

No, an IP datagram is not a fixed-length datagram. The length of an IP datagram can vary depending on the size of the data being transmitted, with the header typically being a minimum of 20 bytes and up to 60 bytes if options are included. The total length of the datagram, including both the header and the data payload, can vary from 20 bytes to 65,535 bytes, as specified by the IP protocol.