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"The IPv4 addresses we?re all used to seeing are made up of four numerical octets"

I think the word you're searching for is "four DECIMAL octets" since hexadecimal is still technically "numerical". Even so, this still isn't correct as IPv4 is equally capable of being expressed as hexadecimal. Try this...

ping 0x7f.0.0.1

...that should work just fine.