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16

The only reasons I would see them arbitrarily choosing 127 is that it's an easy number to remember (01111111), and perhaps they were allowing 16 million host addresses for being able to communicate with itself and itself only (like how some programs and Windows components use ports nowadays). The RFCs only really mentioned that it's standard practice for 127.0.0.1/32 to be used for loopback. It's quite nebulous as to what they intended for the rest of the block aside from it looping back to the host and never hitting the network, hence my above speculation.
– RoyalKnight
Commented Aug 29, 2009 at 23:27
3

Having all the block addresses reverting to 127.0.0.1 is implementation dependent and might perhaps just be a Linux stack peculiarity. Solaris at least requires an interface to be bound to the destination address for your ping test to succeed.
– jlliagre
Commented Jan 20, 2011 at 1:22
The two answers below by Joseph Bui and Dario Fumagalli are brilliant at describing why 127 was chosen. In fact, I don't think it's fair to say 127 was chosen as much as it was its destiny to be used due to its specific properties in the binary world.
– David Storfer
Commented Feb 15 at 19:59

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