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Groups > alt.comp.os.windows-10 > #194697
| From | "Carlos E. R." <robin_listas@es.invalid> |
|---|---|
| Newsgroups | alt.comp.software.firefox, alt.os.linux, comp.mobile.android, alt.internet.wireless, alt.comp.os.windows-10 |
| Subject | Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix |
| Date | 2026-07-21 19:28 +0200 |
| Message-ID | <nc9ohnFc5a2U5@mid.individual.net> (permalink) |
| References | <113kg6k$s72$1@nnrp.usenet.blueworldhosting.com> <nc6h3vF167tU1@mid.individual.net> <113n4f1$1chl$1@nnrp.usenet.blueworldhosting.com> <nc8rrqFc5a3U1@mid.individual.net> <113nlki$1k8p$1@nnrp.usenet.blueworldhosting.com> |
Cross-posted to 5 groups.
On 2026-07-21 13:36, Maria Sophia wrote:
> Carlos E. R. wrote:
>> There are several ways to disable IPv6 on Linux, depending on whether
>> you want the change to be temporary or permanent.
>
> I agree with everything Carlos suggested, where I ran a few searches to
> help everyone on these newsgroups test, right now, their IPv6 protection.
>
There is another trick in Linux to make the system prefer IPv4 over IPv6
if both exist. Idon't remember what it was, so again I asked ChatGPT,
and yes, that was it:
Yes. You're probably thinking of **changing the address selection
policy** so that applications **prefer IPv4 over IPv6** rather than
disabling IPv6 entirely.
On systems using the GNU C Library (`glibc`), this is controlled by
`/etc/gai.conf`.
Edit:
```bash
sudo nano /etc/gai.conf
```
Find this line:
```text
#precedence ::ffff:0:0/96 100
```
Uncomment it:
```text
precedence ::ffff:0:0/96 100
```
This gives IPv4-mapped addresses a higher precedence, causing
`getaddrinfo()` to return IPv4 addresses before IPv6 ones in most cases.
### What this does
Suppose a host has both:
```
example.com
├── A 203.0.113.5
└── AAAA 2001:db8::5
```
Normally, many Linux systems will try the IPv6 address first.
With the `gai.conf` change, most applications will instead connect to
the IPv4 address first.
### What it does *not* do
* It **does not disable IPv6**.
* Applications that explicitly request IPv6 can still use it.
* Programs that don't use `getaddrinfo()` or implement their own address
selection may ignore this preference.
### Why it exists
This mechanism follows the address selection rules defined in RFC 6724.
The default policy prefers IPv6, but `gai.conf` allows administrators to
override the precedence.
### Is this useful for avoiding VPN leaks?
Not really. It reduces the chance that applications will choose IPv6,
but it doesn't eliminate it. If your concern is privacy or ensuring that
**all** traffic goes through a VPN, the correct solution is one of:
* use a VPN that tunnels both IPv4 and IPv6,
* configure the VPN to disable IPv6 while connected, or
* disable IPv6 system-wide.
Changing `gai.conf` is more appropriate when you have a network where
IPv6 technically works but performs poorly or is unreliable, and you
want applications to favor IPv4 without removing IPv6 support altogether.
> Below are some IPv6 leak tests I think everyone should run at least once.
>
> We're all working together as I'll wager many of us on these ngs were as
> unaware as I was that IPv6 is, by design, a privacy hole par excellence.
>
> Reaffirming that this whole IPv6 privacy thing is new to me and that it
> floored me when I found out how different it is from IPv4, to test if the
> Windows or Linux or Android methods are working, these commands may help.
>
> 1. Test external visibility
> start firefox https://test-ipv6.com (Windows)
> firefox https://test-ipv6.com (Linux)
> xdg-open https://test-ipv6.com (Android Termux)
> 2. Check external reachability
> ping -6 google.com
> 3. Identify the local interface configuration
> a. ipconfig (Windows)
> b. ifconfig / ip a (Linux)
> c. Termux > pkg install iproute2 > ip a (Android)
> d. Termux > pkg install net-tools > ifconfig (Android
> 4. Test DNS resolution
> nslookup -type=AAAA google.com (Windows)
> dig AAAA google.com (Linux, Android Termux)
> 5. Test IPv6 routing table
> route print -6 (Windows)
> ip -6 route (Linux/Android Termux)
> 6. Test IPv6 WebRTC leaks
> firefox https://browserleaks.com/webrtc
> firefox https://ipleak.net
> 7. Test IPv6 prefix delegation
> dhclient -6 -v (Linux/Android Termux)
> 8. Test for VPN leaks
> firefox https://ipleak.net
> firefox https://browserleaks.com/ip
> 9. Router setup
> Netgear > Advanced > Advanced Setup > IPv6 > Internet Connection Type
> Disabled (IPv6 is completely off)
> Auto Detect (Router tries to detect IPv6 from your ISP)
> 6to4 Tunnel (Legacy IPv6-over-IPv4 tunneling)
> Pass Through (Router passes IPv6 directly to LAN devices)
> Fixed (Manual IPv6 configuration)
> DHCP (Used when the ISP hands out IPv6 via DHCPv6)
> PPPoE (Used by DSL providers)
> Auto Config (Router uses SLAAC (stateless autoconfiguration)
> 6rd Tunnel (An IPv6-over-IPv4 method used by some ISPs)
> Dual-Stack Lite (Used by ISPs that provide IPv6 but tunnel IPv4.\)
> v6plus (Japan-specific IPv6 service)
>
> For example
> a. No IPv6 addresses were detected by https://test-ipv6.com
> b. ping -6 google.com fails
> c. My Windows host only has link-local IPv6 (fe80::...)
> d. I have no global IPv6 (2000::/3)
> e. I have no IPv6 default gateway
> f. I have no IPv6 DNS
> g. All IPv6-only sites timed out
>
> Specifically for https://test-ipv6.com my IPv6 Firefox score was 0/10
> Test with IPv4 DNS record = ok (2.421s) using ipv4
> Test with IPv6 DNS record = timeout (5.611s)
> Test with Dual Stack DNS record = ok (2.821s) using ipv4
> Test for Dual Stack DNS and large packet = ok (1.230s) using ipv4
> Test IPv6 large packet = bad (3.898s)
> Test if your ISP's DNS server uses IPv6 = ok (1.293) using ipv4
> Find IPv4 Service Provider = ok (2.300s) using ipv4
> Find IPv6 Service Provider = bad (3.815s)
>
> May I ask others out there what your IPv6 results were with Firefox?
My ISP does not provide IPv6 at all to homes. There was a Beta testing
of IPv6, and for two months I had it.
However, it does on mobile phones. On my phone I get an IPv6, and also
an IPv4 on the 10.*.*.* range, thus using GNAT.
--
Cheers,
Carlos E.R.
ES🇪🇸, EU🇪🇺;
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PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-20 02:45 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-20 14:03 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 02:43 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 11:18 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 07:36 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 19:28 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 14:32 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Hank Rogers <Hank@nospam.invalid> - 2026-07-21 18:31 -0500
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 15:40 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 18:53 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Brian Gregory <void-invalid-dead-dontuse@email.invalid> - 2026-07-28 00:36 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix David Higton <dave@davehigton.me.uk> - 2026-07-20 20:47 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-20 21:59 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 02:04 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Adam H. Kerman" <ahk@chinet.com> - 2026-07-21 06:37 +0000
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 03:23 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-21 07:59 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 04:41 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 11:03 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 05:47 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 12:27 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 14:10 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 10:53 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 05:19 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix "Carlos E. R." <robin_listas@es.invalid> - 2026-07-21 11:30 +0200
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 06:10 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 19:13 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-22 09:47 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 16:30 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Brian Gregory <void-invalid-dead-dontuse@email.invalid> - 2026-07-22 21:35 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 16:46 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Brian Gregory <void-invalid-dead-dontuse@email.invalid> - 2026-07-23 04:33 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-23 08:12 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-23 16:23 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Oregonian Haruspex <no_email@invalid.invalid> - 2026-07-25 04:58 +0000
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-26 14:25 -0700
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 01:38 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-21 07:51 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-21 03:45 -0400
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Nuno Silva <nunojsilva@invalid.invalid> - 2026-07-22 09:37 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-24 11:36 -0700
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Brian Gregory <void-invalid-dead-dontuse@email.invalid> - 2026-07-22 21:32 +0100
Re: PSA: IPv6 browser privacy leaks are caused by the host yet there's a simple fix Maria Sophia <mariasophia@comprehension.com> - 2026-07-22 16:54 -0400
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