About UDP...

Recently, I have learned that the UDP checksum is optional, i.e. the value can be zero, which means not to be calculated.
When I got to know, I thought that this was one of a interesting specification of UDP.
In version 6, UDP checksum is mandatory. This has nothing to do with dedicated programmers or ... others.

Its useful for some built-in software which is to be as light as possible. In not the case it indicates to be a tool not using stack , instead of .. raw socket.