If you look at the code, you will see that if you try to write a buffer that is larger than the the maximal length you can write, in DTLS you will fail.
If you are referring to fragmantation in the DTLS layer, this is not supported yet.
However, if you call
mbedtls_ssl_write() with differnt chunks of the same buffer, it should work, as long you have support on the remote peer, that will know how to assemble the chunks into one buffer. Note that since this is an unreliable transport layer, some packets might get lost or arrive in a different order. If you don’t have control on the remote peer, I doubt this will work.
In other words, although technically you will be able to sends the chunks, unless you have a way to reassemble those chunks in the remote peer, in the application layer ( note that the buffer is fragmented to chunks in the application layer), you might get unexpected results.
Mbed TLS Team member,