[3.12] pythongh-124217, ipaddress: Add RFC 9637 reserved IPv6 block 3fff::/20 (pythonGH-124240) (python#124283)

pythongh-124217, ipaddress: Add RFC 9637 reserved IPv6 block `3fff::/20` (pythonGH-124240)
(cherry picked from commit db6eb36)

Signed-off-by: y5c4l3 <[email protected]>
Co-authored-by: Y5 <[email protected]>

Author: miss-islington

Lib/ipaddress.py

@@ -2347,6 +2347,8 @@ class _IPv6Constants:
         IPv6Network('2001:db8::/32'),
         # IANA says N/A, let's consider it not globally reachable to be safe
         IPv6Network('2002::/16'),
+        # RFC 9637: https://www.rfc-editor.org/rfc/rfc9637.html#section-6-2.2
+        IPv6Network('3fff::/20'),
         IPv6Network('fc00::/7'),
         IPv6Network('fe80::/10'),
         ]

Lib/test/test_ipaddress.py

@@ -2408,6 +2408,8 @@ def testReservedIpv6(self):
         self.assertTrue(ipaddress.ip_address('2001:30::').is_global)
         self.assertFalse(ipaddress.ip_address('2001:40::').is_global)
         self.assertFalse(ipaddress.ip_address('2002::').is_global)
+        # gh-124217: conform with RFC 9637
+        self.assertFalse(ipaddress.ip_address('3fff::').is_global)
 
         # some generic IETF reserved addresses
         self.assertEqual(True, ipaddress.ip_address('100::').is_reserved)

Misc/NEWS.d/next/Library/2024-09-19-20-15-00.gh-issue-124217.j0KlQB.rst

@@ -0,0 +1 @@
+Add RFC 9637 reserved IPv6 block ``3fff::/20`` in :mod:`ipaddress` module.