The CCNA books from Cisco Press say 127.0.0.0 is a class A network but is only for diagnostics. The Test Out course says 127.0.0.0 is not included in any class of addresses. What would be the correct answer on the 640-801?
The network 127.0.0.0 is indeed reserved for test purposes. Perhaps the most famous address within it is the universal loopback address, 127.0.0.1. This is a standard feature of every TCP/IP implementation so you can't use it elsewhere for 'real' communications. It is usually set up so that if you ping 127.0.0.anything on your machine then 127.0.0.1 will reply. Hence the whole 127 network is reserved for test