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Comment by AaronFriel | Hacker News Reader

    I used Ubuntu as an example, but it is hardly the worst offender. We have seen
    Windows machines with more than 300 IPv6 addresses

Wow! I don't operate a very large network, but I do operate an IPv6 network and I've never seen one of our machines use more than 2 addresses. I feel like they've got some other configuration option or oddity going on that's causing a lot of these problems, but I am guessing they're much smarter than I am, so I don't know what to say.

Could someone elaborate on this? I've never seen this behavior on an IPv6 network, and I'm just running a server or two with radvd and no custom switch configuration.

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I had a raspberry pi on my network via ethernet and saw it had accumulated a ton of IPv6 addresses. Ended up just disabling privacy extensions on it. If your machines reset their network connection (ie wireless reconnects) then they'll flush their IPv6 privacy addresses.

Your machines might just have a long timeout before they use a new privacy address. You can find more info here: https://home.regit.org/2011/04/ipv6-privacy/

Set your reachable and valid lifetimes to the max. Though you will still end up cycling through some of the privacy address, it's not going to be bad.

Do you use privacy addresses ?

I don't, the /64 is identifiable as "my house" so there is no reason to hide which particular machine is doing something.

A house may have multiple people living there, multiple devices, visitors, etc.

You could track a person connecting through multiple locations by using their MAC address used to assign their IP. i.e. if I am connecting with my laptop from various places, my IP address will be roughly the same, only the network prefix will change.

A house could have multiple users, mine doesn't.

I would maybe see turning on privacy addresses as part of a general "leaving home" script that also turned on other stuff like the firewall.

You are completely right. Privacy IPv6 address are an illusion when used in a household that has effectively an active /64 per subscriber.

(Those who say "but IPv4..." last time my IPv4 address changed, was half a year ago). Anyway this is mostly a political give-in, that happens to also help ruggedize the rest of the stack (the relatively rapid change of privacy addresses uncovers more bugs than we'd otherwise find - so from that standpoint they're to be advocated). But privacy.. huh.

Last IETF there was precisely this discussion that one might want to force a new /64 on themselves, and privacy addresses have nothing to do with that. (DHC WG, FWIW).

Comcast is more than willing to send you more than one /64 prefix if you ask for it!

"effectively an active /64". Comcast folks did a ton of testing with the CPEs, and very very few could ask for anything than an active /64, that's why this qualifier :-)

There's active (and pretty cool) work in the HomeNet IETF workgroup, with running code and all (http://www.homewrt.org/doku.php) to make the multi-subnet home network a sane reality.

But a different /64 from within the same /56 helps not much, and indeed to correctly reflect the spirit of the discussion in the DHC working group, would be to say "I want to be able to press a button and release my currently used allocation and get some completely new one, be it /48, /56 or whatever".

Thanks for the correction!

The proper solution is Stable Privacy addresses, recently standardized in RFC7217 [1]. The interface ID is essentially hash(secret || prefix || mac-address), so it stays the same when you're on the same network, but changes as soon as you go somewhere else.

[1] https://tools.ietf.org/html/rfc7217

But that defeats the purpose of a privacy address. The idea is precisely not to use your address as a way to track individual users, like a cookie tattooed on your skin. I fail to see how a hash of the MAC address is better than the MAC address itself.

Because even with traditional privacy addresses, the first 64 bits of your address never change, and you can be tracked that way. If you happen to share those first 64 bits with many other people, then privacy addresses provide value, but that's simply not the case on your home network.

Now keep in mind that a stable privacy interface ID is not a hash of just the MAC address, it's also a hash of the network prefix and a secret that's specific to your system. Including the prefix ensures that the interface ID changes completely when you move to a different network, preventing you from being tracked all over the world. Including a secret ensures that someone can't build a lookup table from MAC address||prefix to stable privacy interface ID. So it's quite superior to using just the MAC address.

Not really, how many networks do you use in a week. Perhaps 3 or 4. And with this, once a link has been established between the IP, it becomes a permanent static link. It is trivial for advertisers through browser cookies to establish this link, and they only need to do it once.

If you're letting yourself be tracked through your web browser, it really doesn't matter what IP address you use.

You say that like if I was actively letting myself track.

I block third party cookies, I use AdBlockPlus. But I can't block all cookies and html5 storage (most websites wouldn't work anymore). And it only takes one website to see me coming with the same cookie from different IPs to establish that link (take a pick: google, facebook, twitter, etc). And once that link is established it will be pretty valuable (as it is static) and you can bet that these boys will exploit it.

So to me RFC7217 is pretty much as bad as static addresses.

I'm not sure why websites would even care what IP address you're coming from if they've got a cookie, which provides an even stronger way to track you. They might care what the network prefix is, since that would identify your geographical location, but not even privacy extensions prevent that.

responding to your comment below.

You have ways to block third party cookies so that you cannot be tracked on the internet but if you have a website that is advertising focused (say google) and see you coming from two different IPs (and it doesn't need to be a third party website, it can be just when you search something on google), then it will be able to associate these IPs to your profile. Then every time you visit another website, that website will be able to get from google your ID from your IPs even if you block third party cookies. And this is the end of privacy.

If privacy addresses pose multicast problems, then the multicast protocol or implementation needs to be fixed. But static IP addresses isn't the solution.

I think you're putting too much faith in blocking third party cookies. Through collusion with Google (such as an IFRAME or JSONP), sites can get your Google ID from your Google cookie without needing to consult your IP address or use third party cookies. Web browsers open up such a huge can of privacy worms that I don't think it's very useful to talk about IP addresses until you fix the browser.

Personally, I clear all cookies, cache, and local storage (except from a handful of trusted sites, Google not being one) when I exit my browser (and I exit my browser often), and I occasionally examine my browser profile for traces of super-cookies. (And even this is probably not sufficient because of browser fingerprinting.) I don't think privacy extensions provide an appreciable privacy improvement over stable privacy addresses.

Time to participate in open wifi or a mesh network :-)

I find the Privacy addresses a pain when it comes to managing traffic on my network. My (mostly Apple) devices will never use their DHCP provided v6 address to connect to a public service and this means that my gateway doesn't know what the hostname is for that connection.

I ended up writing a little script to scan the "ip -6 neigh" and correlate hosts together based on MAC, then write that to a hosts file for DNSMasq to use. Hack, but it works for me.

I use privacy addresses even while I am at home. Yes, a /64 identifies my house, it doesn't identify all of the people in it.

In fact you know it's a home, but an advertiser has no way to tell. It could be a restaurant, an office, a flatshare, a gym or anything else. If they see two IPs on the same /64, all they can assume is some form of weak correlation.

Correlating "stable privacy addresses" (cf agwa comment) is trivial. How many network do we use in a day? Home, office, mobile provider, perhaps a couple more. Chances are that advertisers will see you using the same cookie across multiple networks and if your IPv6 address is persistent then you can bet that within a week all your stable IPv6 will be mapped to your profile. It only takes one observation to establish the link and then it is a static link.

Ideally you would like your /64 to be renewed regularly (it's not a bad idea to reboot the modem from time to time anyway) and to have randomized IPv6 addresses.

I just checked a couple of freebsd 10 boxes I have. Both have 5 addresses in 'deprecated autoconf temporary' state, and 1 in the 'autoconf temporary' state.

Privacy addresses are enabled via these sysctls:

  * net.inet6.ip6.use_tempaddr (default 0)
    use temporary (privacy) ip6 addresses

  * net.inet6.ip6.prefer_tempaddr (default 0)
    prefer them over the default ip6 address for egress

The lifetimes are controlled via sysctls:

  * net.inet6.ip6.temppltime (defaults to 86400)
    Specifies the “preferred lifetime” for privacy addresses

  * net.inet6.ip6.tempvltime (defaults to 604800)
    Specifies the “valid lifetime” for privacy addresses

So if private addresses are enabled.. by default a temporary ip6 address is changed every 24 hours, and will linger for 7 days. However, they are not enabled by default on freebsd 10.

They're enabled on quite some of the Linux distros. And if someone did not know the consequences of what they were doing when they decided to play with the reachable/valid lifetimes on the prefix, they could end up with a lot of addresses.

I'd love to know more on the origin of the story to understand how we can fix the defaults in IPv6 so they do not blow people's network - but I have a vague feeling someone played with them anyway.

You may find https://communities.intel.com/thread/48051 and similar useful; I've run across mention of it before but have not personally encountered it (but we don't usually have WoL enabled, so...)

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