actually it depends, it depends on the used Protocol.

If you use ISO Transport, TCP, ISO on TCP than you canreceive up to 8192 Byte.
If you use UDP you can only receive up to 2048 Byte.

But... please be aware that the Receive Buffer, especially if you use the TCP Protocol, is only transferred to the CPU if the Buffer is completely filled.

Best regards

I hope this FAQ will help you to understand the circumstances:

What properties, advantages and special features does the TCP protocol offer?

Hopefully I could get you a step further.

Best regards