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Comment by jedberg | Hacker News Reader

IPv6 improves this situation (now). At first, ipv6 was actually a lot worse, since the back 1/2 of your address was your MAC address, allowing your device to be tracked around the internet no matter where it went.

People quickly realized this flaw, and updated the standard so that basically your client gets to pick the second 1/2 of your address now. And the nice thing is, most major platforms will actually run multiple addresses in parallel, allowing new connections to use a new address while old connections keep using the old one.

So while ipv4 adds some protection by having multiple clients behind the firewall, ipv6 actually makes it better by looking like even more clients behind the firewall.

Combined with a browser that blocks fingerprinting you get slightly better privacy with ipv6.

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Absolutely not. Most ISPs will allocate you a fixed /64. You may well have privacy IPs in this /64, the prefix will always be the same.. A though day for privacy activists

Sure, just like with an IPv4 they allocate you a fixed /32.

But you get slightly more privacy by having the client able to randomize the other 1/2 of the address and use multiple addresses, which would confuse trackers. Or the trackers just look at the first /64 and ignore the rest and you're no worse off than you were with your ipV4 /32.

You are worse off as now you have some introspection into computers on the other side of that firewall; with NAT you could have thousands of computers and they would all get melded together as one, but unless you very carefully generate a new IP address for every single connection you make (which is how you can get back to where you were with NAT), you now have the ability to somewhat differentiate users who before would have been mixed. So it is at best the same but probably worse, at which point why not use the thing that is always at least as good if not much better?...

Sounds like we need shorter IPv6 leases and more rotation between the prefixes, but that somehow goes a bit against what IPv6 should provide us - freedom to hold on to an address.

Some systems already have a solution for this, since devices can have multiple IPv6 addresses at once. They have one permanent IPv6 address which is not used for outgoing connections but can be used for incoming connections, and then temporary IPv6 addresses used for outgoing connections which can be rotated arbitrarily often. The first address is permanent but can only be used if you already know it.

An improvement on this would for services to request the machine to hold a specific address, permitted if the address is valid on the current network and not already in use. Then services could each have their own address (generated on first use and then requested when they start) which is effectively permanent but not the same as the addresses used by other services on the same machine.

It's a wash, I think. Anyone who cares uses VPNs and/or Tor. You can do either IPv4 or IPv6 with VPNs, but the methodology is different. With IPv4, it's just NAT. With IPv6, VPN servers must assign a public address. And with Tor, sites only see the exit address.

>just like with an IPv4 they allocate you a fixed /32

Many (most?) ISPs that give you unique IPv4 addresses also use dynamic pools. Just reconnect your router and blend into the pool. Or, if you're behind NAT, you're already indistinguishable from others.

My router is connected for months on end, and I think this is the norm, not an exception. Even if I reconnect, most of the time my provider assigns me the same IP. The only solution here is a good VPN.

When I first installed my connection, provider forcefully disconnected my router every 23 (yes, 23) hours to prevent me from having static ip (and hosting servers on fast home connection). Now it seems my public ipv4 actually changes every several minutes, probably some kind of ipv6to4 gate. But ipv6 of one computer is unchanged since several years.

What do you mean by fixed /32? A PPP link?

> Most ISPs will allocate you a fixed /64

not really. the case where someone in a household power-cycles the router and it gets a new ipv6-addy and then one has to power-cycle all networked devices too because they have no way of knowing that the old prefix is dead, is very common.

To add on this,many will allocate a much smaller prefix. If you are being tracked by IP, the whois of your v6 address will contain what prefix is delegated,but even if they don't use whois they can simply track "subnets" (prefixes) as a data point, if a cookie or browser fingerprint is seen on multiple addresses, the address part will help pin point a specific user.

With v4 you have NAT and CGNAT now that obscures your public address a bit, you lose that with v6. For privacy, you need your address to be shared by many other users. This is one reason VPNs are useful, your public IP is shared by many. It's the same problem with browser fingerprinting, the more you try to prevent it, the more trackable data points you create (e.g.: one more extension or one less default setting that makes you a few steps more unique than everyone else).

Unless you have many thousands of devices on your network, I can't see it actually having any practical advantage. I have maybe a dozen devices on my network, that is going to require only a tiny amount of entropy to uniquely identify the devices, in conjunction with the first half of the address. You wouldn't even need an entire UA string in many cases. Resist fingerprinting != prevent fingerprinting.

The resist fingerprinting measures in browsers are intended to help you blend in with millions of other devices. You'll still likely stand out like a sore thumb if the sample size is your household.

With IPv6 one user is a /64 whereas with IPv4 one user is a /32. That's about equal from a privacy perspective.

But then in reality one IPv4 /32 is often many users due to NAT. Doesn't that make privacy better with v4?

In my experience, in the same cases that IPv4 would have multiple users behind one /32, IPv6 would have multiple users behind one /64.

Except now you are potentially leaking information about the individual computers in the lower 64 bits; if you generate those randomly for every single connection then you can mitigate that, but is that how this is actually being implemented or are they just doing periodic cycling? With NAT you were just guaranteed that this would always be safe.

> With NAT you were just guaranteed that this would always be safe.

Another safety benefit of NAT is that if you use a private IP address block (ex 192.168/16) you can be reasonably certain that your devices aren't publicly routable without bothering to actually check the router firewall configuration. This is particularly nice for home networks - I don't usually want my home devices to be reachable from the internet at large.

To understand what I'm getting at here, imagine trying to walk an elderly relative through verifying their firewall configuration over the phone. A simple command to check the IP address was enough with NAT.

In mobile networks I've only ever seen one UE get one /64, meaning most IPv6 users in the world does not share their /64 with anyone else, if I'm not very mistaken. I think this is standardized in 3GPP but I won't dig for it.

Other sites should get a /56, including home users. That's in RFC 6177. This is a best practice RFC of "shoulds" rather than "musts" so technically it's still IPv6 if your ISP only give you a /64 for your site... but it's wrong.

Your LAN devices (if you only have one LAN in your site, typical for a home) could still all be in the same /64. But the difference between one home and one person is small in the context of tracking for purposes of advertisement and besides, the trackers get extra bits per device which were hidden when the same devices were behind one IPv4 NAT. Poorly hidden, as all devices probably had different user-agents or resolutions and a hundred other things to fingerprint anyway but still, slightly less accessible.

That seems backwards: with NAT you couldn't identify all of the individual computers on my Internet connection; but now, with IPv6, you either can at worst (as every device has its own IP address that it reuses) or, at best (generating a new address for every single connection), are just getting yourself back to where you were with NAT. I appreciate that for a while IPv6 was actively much worse as it allowed address correlation across multiple networks (due to the MAC address being the same in the lower 64 bits), but fixing that doesn't make it better than NAT: if you mostly care about privacy, it still seems to make the most sense to use NAT if at all possible.

> with NAT you couldn't identify all of the individual computers on my Internet connection...

Not if you're using WebRTC which would promptly leak the private IP address: https://news.ycombinator.com/item?id=12528184

There are also several other methods that often work, e.g. the X-Forwarded-For HTTP header if there is a local proxy, or a long list of non-HTTP protocols or tunnel-XYZ-inside-HTTP protocols that have the client IP as part of the protocol.

Temporary IPv6 addresses actually solve this, especially for P2P systems that do benefit from knowing the client IP in case there is a peer on the same LAN, because the address they get is the same one the remote server sees (no additional information) and then it's both a valid local address but hard to correlate with anything when every device can have hundreds of them at once.

> so that basically your client gets to pick the second 1/2 of your address now. And the nice thing is, most major platforms will actually run multiple addresses in parallel, allowing new connections to use a new address while old connections keep using the old one.

This is really interesting and I was not aware of this. Are there any links where I can read about this more? I tried searching around, but did not find anything.

Here's Wikipedia [1] and the RFC [2].

As noted, Mac OS, Windows and Linux already implement this.

[1]https://en.wikipedia.org/wiki/IPv6_address#Temporary_address...

[2]https://tools.ietf.org/html/rfc4941

I didn’t get your description of IPv6 offering better privacy protection.

With IPv6, your ISP could give you one address for each of your devices for life without any grudges or pain, assuming it doesn’t mind losing out on the static IP add on pricing that some charge in the scarce IPv4 space. That would enable better long term tracking without additional tokens (like cookies) and fingerprinting. We’ll never run out of IPv6 addresses.

Your ISP only assigned you the first 1/2 of the address. You get to pick the second 1/2 yourself. Your client can (and in most cases will) constantly switch up the second 1/2 of the address.

Is that required, or only by convention? Ie could an ISP hypothetically choose to allocate a full IPv6 address to you?

Sure, they could assign you a /128 for your connection to them. In fact, I imagine there are some ISPs out there that do just that.

Which means that trackers will still track you, but only based on the first 1/2 of your IPv6 address. Since that doesn't change (often) it's essentially as fixed as your old /32 IPv4 address was.

> you get slightly better privacy with ipv6

its a larger identifying token serving less users, so no.

You're thinking mathematically, not practically.

come again?

One can very easily change MAC address though, it's not like that is an insurmountable issue, right?

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