Description:
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From manual page: http://www.php.net/filter.filters.validate
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The FILTER_VALIDATE_IP ignores short notations of IPv4 address (e.g. "127.1") and falsely reports them to not be valid IP Addresses.
It somehow manages to recognize short forms of IPv6 addresses though (e.g. "::1").

Btw, simple telnet manages to recognize 'em:
$ telnet 127.1 22
Trying 127.0.0.1...
Connected to 127.1.
Escape character is '^]'.
SSH-2.0-OpenSSH_7.2p2 Ubuntu-4ubuntu2.2

Test script:
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#!/bin/bash

php -r 'var_dump( filter_var("127.1", FILTER_VALIDATE_IP) );'

Expected result:
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string(5) "127.1"

Actual result:
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bool(false)