Closed Bug 1655775 Opened 4 years ago Closed 4 years ago

Wrong IPv6 in cache


(Core :: Networking: DNS, defect)

78 Branch



Tracking Status
firefox-esr78 --- wontfix


(Reporter: clement+mozilla, Unassigned, NeedInfo)



(1 file)

Attached image firefox.svg.png

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:78.0) Gecko/20100101 Firefox/78.0

Steps to reproduce:

When I visit or, Firefox sometimes display instead.

The top image shows the first visit of, then I visit, see middle screenshot, and finally, I visit again, see bottom screenshot.

Actual results:

Sometimes Firefox is having a wrong IPv6 in cache. Using the extension SixOrNot, I can see for the following IPv6 2001:41d0:fecf:8900:216:3eff:fe65:97bc, with the label "Cache". However, this IP corresponds to and the actual IPv6 for is 2001:41d0:fecf:8900:216:3eff:fef1:20a2.

It is not linked to the extension SixOrNot. Indeed, I have the same issue with other computers on my network which don't have this extension installed.
They are also using different DNS resolvers, which makes me wonder if Firefox is ignoring the system DNS resolvers.
DoH is disabled.
For all tested computers, other web browsers are working properly, tested with w3m and Chromium.

I thought that it can come from DNS Prefetching, however, there is no X-DNS-Prefetch-Control in any of the HTTP headers for any of the involved website.
I guess that if it was about cache and cookies, the issue would not be random.

about:networking#dnslookuptool shows correct AAAA entries even when Firefox is having the wrong IPv6 in cache.

Expected results:

Firefox should have cached the IPv6 corresponding to the website, not another one.

Hi Clément Février,
I tried replicating this on my end using Ubuntu 18.04.3 LTS and Windows 10 pro. When you say "Firefox sometimes display instead." how often does this happen to you? After how many visits?

Can you attach you about:support please?

Please test if the issue occurs to you in safe mode (add-ons disabled). Here is a link that can help you do that:

If the issue persists, also test it using a fresh profile, you can find the steps to do that below:

Also, try this on the latest version of nightly. You can download it from here:

I will move this over to a component so developers can take a look over it. If is not the correct component please feel free to change it to an appropriate one.

Thanks for the report.

Best regards, Clara.

Component: Untriaged → DOM: Navigation
Product: Firefox → Core
Flags: needinfo?(clement+mozilla)

Moving to Networking component

Component: DOM: Navigation → Networking: DNS
Closed: 4 years ago
Resolution: --- → DUPLICATE
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