My FreeBSD VM has a NIC with the IPv6 address fe80::5054:ff:fe9: local-link IPv6 address. It's used by uuid._netstat_getnode() as a MAC address, but it seems like this IPv6 address doesn't respect RFC 4122 and so should be skipped. _find_mac_under_heading() should reject IPv6 address: only use MAC address. vstinner@freebsd$ uname -a FreeBSD freebsd 12.1-RELEASE-p2 FreeBSD 12.1-RELEASE-p2 GENERIC amd64 ====================================================================== FAIL: test_netstat_getnode (test.test_uuid.TestInternalsWithExtModule) ---------------------------------------------------------------------- Traceback (most recent call last): File "/usr/home/vstinner/python/master/Lib/test/test_uuid.py", line 767, in test_netstat_getnode self.check_node(node, 'netstat') File "/usr/home/vstinner/python/master/Lib/test/test_uuid.py", line 736, in check_node self.assertTrue(0 < node < (1 << 48), AssertionError: False is not true : fe805054fffe9 is not an RFC 4122 node ID ====================================================================== FAIL: test_netstat_getnode (test.test_uuid.TestInternalsWithoutExtModule) ---------------------------------------------------------------------- Traceback (most recent call last): File "/usr/home/vstinner/python/master/Lib/test/test_uuid.py", line 767, in test_netstat_getnode self.check_node(node, 'netstat') File "/usr/home/vstinner/python/master/Lib/test/test_uuid.py", line 736, in check_node self.assertTrue(0 < node < (1 << 48), AssertionError: False is not true : fe805054fffe9 is not an RFC 4122 node ID It's using a qemu VM run by virt-manager. fe805054fffe9 seems to be the MAC address of my vtnet network interface: vstinner@freebsd$ netstat -ian Name Mtu Network Address Ipkts Ierrs Idrop Opkts Oerrs Coll vtnet 1500 <Link#1> 52:54:00:9d:0e:67 10017 0 0 8174 0 0 vtnet - fe80::%vtnet0 fe80::5054:ff:fe9 0 - - 4 - - vtnet - 192.168.122.0 192.168.122.45 8844 - - 8171 - - lo0 16384 <Link#2> lo0 260148 0 0 260148 0 0 lo0 - ::1/128 ::1 193 - - 193 - - ff01::1%lo0 ff02::2:2eb7:74fa ff02::2:ff2e:b774 ff02::1%lo0 ff02::1:ff00:1%lo lo0 - fe80::%lo0/64 fe80::1%lo0 0 - - 0 - - ff01::1%lo0 ff02::2:2eb7:74fa ff02::2:ff2e:b774 ff02::1%lo0 ff02::1:ff00:1%lo lo0 - 127.0.0.0/8 127.0.0.1 259955 - - 259955 - - 224.0.0.1

 New changeset eb886db1e99a15f15a2342aa496197a5f88fa9c8 by Victor Stinner in branch 'master': bpo-39991: uuid._netstat_getnode() ignores IPv6 addresses (GH-19043) https://github.com/python/cpython/commit/eb886db1e99a15f15a2342aa496197a5f88fa9c8 

It seems like this issue is a regression caused by the following change of bpo-28009: commit 0bcbfa43d55d9558cdcb256d8998366281322080 Author: Michael Felt <aixtools@users.noreply.github.com> Date: Thu Sep 26 20:43:15 2019 +0100 bpo-28009: Fix uuid.uuid1() and uuid.get_node() on AIX (GH-8672) which replaced: if len(word) == 17 and word.count(b':') == 5: with: if len(word) == 17:

My fix is incomplete: the IPv6 address "123:2:3:4:5:6:7:8" is a valid IPv6 address and uuid.py accepts it as a valid MAC address, whereas it's not a MAC address.

 New changeset ebf6bb9f5ef032d1646b418ebbb645ea0b217da6 by Victor Stinner in branch 'master': bpo-39991: Enhance uuid parser for MAC address (GH-19045) https://github.com/python/cpython/commit/ebf6bb9f5ef032d1646b418ebbb645ea0b217da6 

Ok, the new stricter parser should now cover all cases. If not, it should be easier to fix it ;-) I close the issue.