gh-151049: Add 2001:1::3/128 (RFC 9665) to ipaddress IPv6 global exceptions

IANA's IPv6 Special-Purpose Address Registry (2024-04) lists 2001:1::3/128
("DNS-SD Service Registration Protocol Anycast", RFC 9665) as globally
reachable, like 2001:1::1/128 and 2001:1::2/128. It was missing from
_IPv6Constants._private_networks_exceptions, so is_global returned False
for it. Add the exception and extend testReservedIpv6.

Author: tonghuaroot

Lib/ipaddress.py

@@ -2394,6 +2394,8 @@ class _IPv6Constants:
     _private_networks_exceptions = [
         IPv6Network('2001:1::1/128'),
         IPv6Network('2001:1::2/128'),
+        # RFC 9665: https://www.rfc-editor.org/rfc/rfc9665.html
+        IPv6Network('2001:1::3/128'),
         IPv6Network('2001:3::/32'),
         IPv6Network('2001:4:112::/48'),
         IPv6Network('2001:20::/28'),

Lib/test/test_ipaddress.py

@@ -2488,6 +2488,10 @@ def testReservedIpv6(self):
         self.assertFalse(ipaddress.ip_address('2001::').is_global)
         self.assertTrue(ipaddress.ip_address('2001:1::1').is_global)
         self.assertTrue(ipaddress.ip_address('2001:1::2').is_global)
+        # gh-151049: RFC 9665 anycast address (IANA 2024-04 registration)
+        self.assertTrue(ipaddress.ip_address('2001:1::3').is_global)
+        self.assertFalse(ipaddress.ip_address('2001:1::3').is_private)
+        self.assertFalse(ipaddress.ip_address('2001:1::4').is_global)
         self.assertFalse(ipaddress.ip_address('2001:2::').is_global)
         self.assertTrue(ipaddress.ip_address('2001:3::').is_global)
         self.assertFalse(ipaddress.ip_address('2001:4::').is_global)

Misc/NEWS.d/next/Library/2026-06-07-23-30-34.gh-issue-151049.mBlToO.rst

@@ -0,0 +1,4 @@
+:mod:`ipaddress`: fix ``is_global`` and ``is_private`` for the
+``2001:1::3/128`` (DNS-SD Service Registration Protocol Anycast) address,
+which IANA registered as globally reachable per :rfc:`9665`. It is now
+correctly reported with ``is_global`` ``True`` and ``is_private`` ``False``.