You're correct in believing that your regex says match one to three digits... but more precisely, it says, match one to three digits before a dot... and if the suspect value you feed it has something before the three-digits-before-a-dot it will match that value, too, ignoring, as does your regex, the number(s) (or letters, symbols, etc) which precede the three-digits-before-a-dot.

Illustrating anchors (where ^ means start of string (to the regex) and $ marks end of string:

# 1148750

print "Testing IP Addresses in array, \@ip: \n";

my @ip = ("0123.456.789.654", 
         "a123.456.789.654",
         "123.456.789.6543",
         "111.222.333.444")
    ;

for $ip (@ip) {
    if ( $ip =~ /(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})/)
    {
     print "yes $ip has a match: $1 $2 $3 $4\n";
    }
    else
    {
     print "no match\n";
    }
}

print "\n\t whereas, with anchors in the ip, \n";

for $ip(@ip) {
    if ( $ip =~ /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/) {
     print "Second regex matches $1 $2 $3 $4\n";
    }
    else
    {
     print "no match in $ip \n";
    }
}

=head execution results:

Testing IP Addresses in array, @ip:
yes 0123.456.789.654 has a match: 123 456 789 654
yes a123.456.789.654 has a match: 123 456 789 654
yes 123.456.789.6543 has a match: 123 456 789 654
yes 111.222.333.444 has a match: 111 222 333 444

         whereas, with anchors in the ip,
no match in 0123.456.789.654
no match in a123.456.789.654
no match in 123.456.789.6543
Second regex matches 111 222 333 444

=cut
[download]

Two Updates in para 1: s/n/in/ and edited for clarity my explanation of what happens when no anchor is specified.