Get most recent global ipv6 address of interface

Question

I'm trying to get the current public ipv6 address of an interface in python. By searching, I discovered the netifaces package, which can give me a list of all ipv6 addresses of the device.

This will include

a link-local address (which I could filter out with a simple hack, which isn't pretty but well...)
several global ipv6 addresses, one of which is the current one

Now what do I mean by current? Through privacy extensions (RFC 4941), a new address is assigned to the interface in regular intervals. Old global ipv6 addresses are still valid, but flagged as deprecated. I want this most recent one.

Here's what I tried (obfuscated parts of the addresses for security reasons):

>>> import netifaces 
>>> addrs = netifaces.ifaddresses('en0')
>>> for i in addrs[netifaces.AF_INET6]:
...     print(i)
...
{'addr': 'fe80::caa:452a:b8cb:862e%en0', 'netmask': 'ffff:ffff:ffff:ffff::/64', 'flags': 1024}
{'addr': '2a02:____:____:9f1:cd8:e__e:e57b:eaa8', 'netmask': 'ffff:ffff:ffff:ffff::/64', 'flags': 1088}
{'addr': '2a02:____:____:9f1:3489:b__7:fb34:101', 'netmask': 'ffff:ffff:ffff:ffff::/64', 'flags': 192}

Obviously, the first is the link-local address. The second and third are the global ones, and they have a flag, of which I have no idea what it means.

Is there any way (perhaps through the flag, or another method in python) to figure out the current (temporary, non-deprecated) global address?

In Linux, I know I could parse the output of ip -o -6 addr show dev interface and parse that output, but that won't work e.g. on a Mac, and parsing output of other tools is something I dislike if there's a python package for it.

EDIT: The flags seem not to be present on every OS. The output above was on a Mac. Here's the output on a Linux machine in the same network (much longer uptime):

{'addr': '2a02:____:____:9f1:940c:f__f:f9c0:c274', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:395a:6__d:650a:3a11', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:d08a:6__d:d967:d28a', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:9d20:b__7:3edc:96a4', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:b584:d__b:16bf:5dd2', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:61ba:d__b:78d8:197f', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:c1df:7__7:236d:4219', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': '2a02:____:____:9f1:d021:4__3:1a44:4947', 'netmask': 'ffff:ffff:ffff:ffff::/64'}
{'addr': 'fe80::17ed:fbf5:a707:2a42%enp4s0', 'netmask': 'ffff:ffff:ffff:ffff::/64'}

EDIT 2:

Since there was some confusion what I mean by "current" addresses, here's what I mean. On the Linux machine of the previous example:

% ip -o -6 addr show dev enp4s0
2: enp4s0    inet6 2a02:____:____:9f1:940c:f__f:f9c0:c274/64 scope global temporary dynamic \       valid_lft 530760sec preferred_lft 12247sec
2: enp4s0    inet6 2a02:____:____:9f1:395a:6__d:650a:3a11/64 scope global temporary deprecated dynamic \       valid_lft 444473sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:d08a:6__d:d967:d28a/64 scope global temporary deprecated dynamic \       valid_lft 358187sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:9d20:b__7:3edc:96a4/64 scope global temporary deprecated dynamic \       valid_lft 271901sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:b584:d__b:16bf:5dd2/64 scope global temporary deprecated dynamic \       valid_lft 185616sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:61ba:d__b:78d8:197f/64 scope global temporary deprecated dynamic \       valid_lft 99330sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:c1df:7__7:236d:4219/64 scope global temporary deprecated dynamic \       valid_lft 13044sec preferred_lft 0sec
2: enp4s0    inet6 2a02:____:____:9f1:d021:4__3:1a44:4947/64 scope global dynamic mngtmpaddr noprefixroute \       valid_lft 2591735sec preferred_lft 604535sec
2: enp4s0    inet6 fe80::17ed:fbf5:a707:2a42/64 scope link noprefixroute \       valid_lft forever preferred_lft forever

Obviously, all the "temporary" addresses are valid addresses. But only one is not flagged deprecated. This address will be used for outbound connections. And this is the one I want.

Good point, that's on a Mac. Apparently there's no flags on linux, which does not make things easier... I'm adding this to the question. — Demosthenes
If you're going to parse something, I'd parse the output of ip route get instead, e.g. ip -6 route get to 2001:4860:4860::8888 This will show the actual source address that will be used for a connection to the given remote address. — Michael Hampton
This will work on Linux, true, but on a Mac, for instance, there's no ip command (by default, you can probably install it). Ideally I'd like a portable solution , and without parsing. But helpful enough I'll give the comment an upvote. — Demosthenes
"several global ipv6 addresses, one of which is the current one" Actually, IPv6 can have multiple current global addresses on a single interface. With IPv4, you had to jump through some hoops to put multiple addresses on a single interface, but that is built right into IPv6. You will have a link-local address, but you can have multiple of each global and ULA addresses on the same interface. — Ron Maupin

Pranav Pranav · Accepted Answer · 2021-02-24T08:58:48

If you want a public IPv6 address then try this.

socket.getaddrinfo(socket.gethostname(), None, socket.AF_INET6)[1][4][0]

Get most recent global ipv6 address of interface

1 Answers