Per Bela, UDP based stacks should use FD_ALL instead of FD. TCP based stacks should not.

FD_ALL works better in cases where X > 1 nodes fail; with FD it will take X * the failure timeout to suspect the Xth node. E.g. 3 nodes C, D, E fail, 30 sec failure timeout, it will be 90 secs before the failure of E is discovered.