This allows us to generate a globally unique ID for any TCP socket. When we say globally, we really mean globally - it should be impossible to have two machines generate the same UUID.
The only case the uniqueness of the UUID could be violated is if two machines have the same hostname and booted up at the exact same second in time, but it is bad practice to give machines the same hostname (so don't).
The design of the UUIDs and this system for creating them can be found in
DESIGN.md
.