UDP datagrams are blocked when fragmented?

Hi! — Oracle Ubuntu 24.04.1 on ARM free tier.

The problem is that UDP works only when the datagram sent is small enough to fit without fragmenting. If it needs to fragment, only the first fragment is transmitted. This breaks all kinds of applications that use UDP.

For example, on the cloud server I do:

netcat -u -l -p 5432

And on the client side:

dd if=/dev/zero bs=1 count=1000 2>/dev/null | base64 | netcat -u 123.123.123.123 5432

…that works fine: I see output on the server side. But if I do on the client side count=1200 instead:

dd if=/dev/zero bs=1 count=1200 2>/dev/null | base64 | netcat -u 123.123.123.123 5432