Issue #13399 has been reported by rtib (Tibor Repasi).

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Bug #13399: IPAddr accepts invalid address mask
https://bugs.ruby-lang.org/issues/13399

* Author: rtib (Tibor Repasi)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.1p111 (2017-03-22 revision 58053) [x86_64-darwin15]
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
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API Class IPAddr can be initialised with e.g. '1.2.3.4/255.255.255.1', which is an invalid mask for an IPv4 address, however, IPAddr.new won't throw ArgumentError, nor ip.ipv4? will return false.

$ cat iptest.rb
require 'ipaddr'

begin
  ip = IPAddr.new('1.2.3.4/255.255.255.1')
rescue ArgumentError
  puts 'ArgumentError was thrown'
end
puts 'IP address is valid' if ip.ipv4?

$ ruby iptest.rb
IP address is valid

$ ipcalc 1.2.3.4/255.255.255.1
INVALID NETMASK
INVALID MASK1:   255.255.255.1

Address:   1.2.3.4              00000001.00000010.00000011. 00000100
Netmask:   255.255.255.0 = 24   11111111.11111111.11111111. 00000000
Wildcard:  0.0.0.255            00000000.00000000.00000000. 11111111
=>
Network:   1.2.3.0/24           00000001.00000010.00000011. 00000000
HostMin:   1.2.3.1              00000001.00000010.00000011. 00000001
HostMax:   1.2.3.254            00000001.00000010.00000011. 11111110
Broadcast: 1.2.3.255            00000001.00000010.00000011. 11111111
Hosts/Net: 254                   Class A





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