I've always wondered how 9000 became "jumbo". Technically anything over 1500 is consider ju!no and there is no standard. The largest I've seen is 16k. I think there are some crc accuracy concerns at larger sizes but 9k still seems quite arbitrary for computer land.
The explanation according to https://web.archive.org/web/20010221204734/http://sd.wareone... is: "First because ethernet uses a 32 bit CRC that loses its effectiveness above about 12000 bytes. And secondly, 9000 was large enough to carry an 8 KB application datagram (e.g. NFS) plus packet header overhead."
That is, 9000 is the first multiple of 1500 which can carry an 8192-byte NFS packet (plus headers), while still being small enough that the Ethernet CRC has a good probability to detect errors.
Ethernet frame size was never strictly limited. The way the packet length works with Ethernet II frames (802.3 is more explicit, but never really caught on) is that the hardware needs to read all the way to the end of the packet and detect a valid CRC and a gap at the end before it knows the thing is done. So there's no reason beyond buffer size to put a fixed limit on it, and different hardware had different SRAM configuration.
