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DNS Error : Firefox resolve wrong Domain/IP

Posted

Hello,

Visitors of my website are having problem with Firefox. The browser is resolving the wrong IP.

Sometimes when they browse www.koreus.com, Firefox doesn't resolve www.koreus.com but it resolves embed.koreus.com instead (one of my subdomains). So It tries to load a webpage that doesn't exist on embed.koreus.com If they ping www.koreus.com , the IP is the good one.

I was also able to reproduce the issue using Firefox on Linux (Ubuntu). I have check the about:networking#dns page when the problem occurs, and the DNS informations are corrects. I tried to disable DNS cache by setting network.dnsCacheEntries at 0 but I still have the issue

Infos :

host www.koreus.com www.koreus.com has address 5.39.70.224 www.koreus.com has IPv6 address 2001:41d0:8:88e0::100

host embed.koreus.com embed.koreus.com is an alias for embed.koreus.me. embed.koreus.me has address 62.210.181.39 embed.koreus.me has address 62.210.201.242 embed.koreus.me has IPv6 address 2001:bc8:323f:100::1 embed.koreus.me has IPv6 address 2001:bc8:323f:200::1 embed.koreus.me has IPv6 address 2001:41d0:8:88e0::100

How to reproduce the issue  ? Go to https://www.koreus.com/videos/nouveau/ and click on "Suivant" button to load another page. After 3/4 pages the problem occurs. You should see the webpage "Erreur DNS" which exist only on the embed.koreus.com server.

If I force reload the page, the good page from www.koreus.com is loaded, which looks like a cache problem. How can I confirm that ? Is it possible to see the DNS Cache ?

Regards, Jerome

Hello, Visitors of my website are having problem with Firefox. The browser is resolving the wrong IP. Sometimes when they browse www.koreus.com, Firefox doesn't resolve www.koreus.com but it resolves embed.koreus.com instead (one of my subdomains). So It tries to load a webpage that doesn't exist on embed.koreus.com If they ping www.koreus.com , the IP is the good one. I was also able to reproduce the issue using Firefox on Linux (Ubuntu). I have check the about:networking#dns page when the problem occurs, and the DNS informations are corrects. I tried to disable DNS cache by setting network.dnsCacheEntries at 0 but I still have the issue Infos : host www.koreus.com www.koreus.com has address 5.39.70.224 www.koreus.com has IPv6 address 2001:41d0:8:88e0::100 host embed.koreus.com embed.koreus.com is an alias for embed.koreus.me. embed.koreus.me has address 62.210.181.39 embed.koreus.me has address 62.210.201.242 embed.koreus.me has IPv6 address 2001:bc8:323f:100::1 embed.koreus.me has IPv6 address 2001:bc8:323f:200::1 embed.koreus.me has IPv6 address 2001:41d0:8:88e0::100 How to reproduce the issue ? Go to https://www.koreus.com/videos/nouveau/ and click on "Suivant" button to load another page. After 3/4 pages the problem occurs. You should see the webpage "Erreur DNS" which exist only on the embed.koreus.com server. If I force reload the page, the good page from www.koreus.com is loaded, which looks like a cache problem. How can I confirm that ? Is it possible to see the DNS Cache ? Regards, Jerome
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Additional System Details

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  • User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:67.0) Gecko/20100101 Firefox/67.0

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Wesley Branton
  • Top 10 Contributor
594 solutions 5017 answers

I'm not able to reproduce the issue on either my Windows 10 or Ubuntu Linux systems. The www.koreus.com website loads fine and the embed.koreus.com/embed.koreus.me domains both forward to www.koreus.com without issues. I'm able to navigate to the next page without running into any issues.

My guess is that it's something with your server configuration, not Firefox. The steps that you have described to reproduce the issue are not consistent with the symptoms of a DNS error. Navigating pages should not trigger a DNS error because your computer will store your server's IP in cache. Therefore, a DNS request will not be made on each page load, so it's unlikely that any DNS issue will occur when changing pages on the same domain.

It's possible that your domain registrar is not updating to every DNS service, so maybe there is one that still has an old IP address. This is common when recent DNS changes are made, since it takes some time for all DNS services to receive changes.

The about:networking page gives you the ability to see the DNS cache along with the expiration time of each cache item. This page also has a DNS Lookup ability to see the IP address associated with specific domains.

You can try having your visitors flush their DNS cache. This will delete the DNS cache and should fix the issue, although it should be unnecessary on a server that is properly configured.

Contacting your host for further assistance could be beneficial in this case.

The only other thing I can recommend is trying Firefox in Safe Mode to see if the issue stops. Although it's unlikely, it's not impossible that an extension (especially a content blocking or filtering one) is redirecting specific requests. Certain security software can have similar effects.

Hope this helps.

I'm not able to reproduce the issue on either my Windows 10 or Ubuntu Linux systems. The www.koreus.com website loads fine and the embed.koreus.com/embed.koreus.me domains both forward to www.koreus.com without issues. I'm able to navigate to the next page without running into any issues. My guess is that it's something with your server configuration, not Firefox. The steps that you have described to reproduce the issue are not consistent with the symptoms of a DNS error. Navigating pages should not trigger a DNS error because your computer will store your server's IP in cache. Therefore, a DNS request will not be made on each page load, so it's unlikely that any DNS issue will occur when changing pages on the same domain. It's possible that your domain registrar is not updating to every DNS service, so maybe there is one that still has an old IP address. This is common when recent DNS changes are made, since it takes some time for all DNS services to receive changes. The <code>about:networking</code> page gives you the ability to see the DNS cache along with the expiration time of each cache item. This page also has a DNS Lookup ability to see the IP address associated with specific domains. You can try having your visitors [https://www.whatsmydns.net/flush-dns.html flush their DNS cache]. This will delete the DNS cache and should fix the issue, although it should be unnecessary on a server that is properly configured. Contacting your host for further assistance could be beneficial in this case. The only other thing I can recommend is [[Troubleshoot Firefox issues using Safe Mode|trying Firefox in Safe Mode]] to see if the issue stops. Although it's unlikely, it's not impossible that an extension (especially a content blocking or filtering one) is redirecting specific requests. Certain security software can have similar effects. Hope this helps.
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Question owner

Thanks for you answer and thanks for you time.

I'm aware the bug is hard to reproduce, so I'm have made a more reliable step by step :

1 - ping embed.koreus.com

Valid IPs for the test : 62.210.201.242 62.210.181.39 192.99.10.164 2001:bc8:323f:200::1 2001:bc8:323f:100::1 2607:5300:60:3ba4::1

IF IP is 5.39.70.224 or 2001:41d0:8:88e0::100 THEN GO step 2 ELSE GO step 4

2 - FlushDNS

To Flush DNS on windows : ipconfig /flushdns To Flush DNS on Ubuntu : sudo systemd-resolve --flush-caches

3 - Go Step 1

4 - Restart Firefox

5 - Open https://embed.koreus.com/test.html

Click on the button to open https://www.koreus.com/test/dns.html?rand=number

6 - Two solutions, you see "DNS Error" or "Test OK"

"Test OK" means you are on the good server

"DNS Error" means you are on the bad server, Firefox tried to open "https://www.koreus.com/test/dns.html?rand=number" on the embed.koreus.com server. If you Force reload (Ctrl+Shift+R) the page you will see the "Test OK". You can go to step 5 to reproduce the error.

Edit : I have edited the step by step

Thanks for you answer and thanks for you time. I'm aware the bug is hard to reproduce, so I'm have made a more reliable step by step : 1 - ping embed.koreus.com Valid IPs for the test : 62.210.201.242 62.210.181.39 192.99.10.164 2001:bc8:323f:200::1 2001:bc8:323f:100::1 2607:5300:60:3ba4::1 IF IP is 5.39.70.224 or 2001:41d0:8:88e0::100 THEN GO step 2 ELSE GO step 4 2 - FlushDNS To Flush DNS on windows : ipconfig /flushdns To Flush DNS on Ubuntu : sudo systemd-resolve --flush-caches 3 - Go Step 1 4 - Restart Firefox 5 - Open https://embed.koreus.com/test.html Click on the button to open https://www.koreus.com/test/dns.html?rand=number 6 - Two solutions, you see "DNS Error" or "Test OK" "Test OK" means you are on the good server "DNS Error" means you are on the bad server, Firefox tried to open "https://www.koreus.com/test/dns.html?rand=number" on the embed.koreus.com server. If you Force reload (Ctrl+Shift+R) the page you will see the "Test OK". You can go to step 5 to reproduce the error. Edit : I have edited the step by step

Modified by Koreus

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WestEnd
  • Top 25 Contributor
60 solutions 5379 answers

It says 404 error....

It says 404 error....
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Question owner

WestEnd said

It says 404 error....

At which step ?

''WestEnd [[#answer-1226098|said]]'' <blockquote> It says 404 error.... </blockquote> At which step ?
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Wesley Branton
  • Top 10 Contributor
594 solutions 5017 answers

I'm sorry, but I'm just not able to reproduce the issue. No matter how many times I ping and flush the DNS, I never get 5.39.70.224 as the IP address for embed.koreus.com. I get 192.99.10.164.

When I finally give up on trying to get the IP that you have stated I should get and proceed through the rest of the steps, I get a 404 error message on step 7 (as WestEnd stated above) because the https://www.koreus.com/test/dns.php file does not exist on your server. But I never get a DNS error message.

Are you able to reproduce the issue in any other browser? This is sounding less and less like a Firefox-related issue.

I'm sorry, but I'm just not able to reproduce the issue. No matter how many times I ping and flush the DNS, I never get <code>5.39.70.224</code> as the IP address for embed.koreus.com. I get <code>192.99.10.164</code>. When I finally give up on trying to get the IP that you have stated I should get and proceed through the rest of the steps, I get a 404 error message on step 7 (as WestEnd stated above) because the https://www.koreus.com/test/dns.php file does not exist on your server. But I never get a DNS error message. Are you able to reproduce the issue in any other browser? This is sounding less and less like a Firefox-related issue.
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Question owner

Well I messed up with the URL https://www.koreus.com/test/dns.php Sorry for the inconvenience. The URL works now. I have also edited the step by step.

If you could make another try :)

Btw, 192.99.10.164 is one of the good IPs for the test.

And I was only able to reproduce the problem on Firefox (Windows 10, MacOS and Linux) I tried on Edge, Chrome and Safari.

Edit : Unable to reproduce with network.dns.disableIPv6 = true

Wesley Branton said

I'm sorry, but I'm just not able to reproduce the issue. No matter how many times I ping and flush the DNS, I never get 5.39.70.224 as the IP address for embed.koreus.com. I get 192.99.10.164. When I finally give up on trying to get the IP that you have stated I should get and proceed through the rest of the steps, I get a 404 error message on step 7 (as WestEnd stated above) because the https://www.koreus.com/test/dns.php file does not exist on your server. But I never get a DNS error message. Are you able to reproduce the issue in any other browser? This is sounding less and less like a Firefox-related issue.
Well I messed up with the URL https://www.koreus.com/test/dns.php Sorry for the inconvenience. The URL works now. I have also edited the step by step. If you could make another try :) Btw, 192.99.10.164 is one of the good IPs for the test. And I was only able to reproduce the problem on Firefox (Windows 10, MacOS and Linux) I tried on Edge, Chrome and Safari. Edit : Unable to reproduce with network.dns.disableIPv6 = true ''Wesley Branton [[#answer-1226107|said]]'' <blockquote> I'm sorry, but I'm just not able to reproduce the issue. No matter how many times I ping and flush the DNS, I never get <code>5.39.70.224</code> as the IP address for embed.koreus.com. I get <code>192.99.10.164</code>. When I finally give up on trying to get the IP that you have stated I should get and proceed through the rest of the steps, I get a 404 error message on step 7 (as WestEnd stated above) because the https://www.koreus.com/test/dns.php file does not exist on your server. But I never get a DNS error message. Are you able to reproduce the issue in any other browser? This is sounding less and less like a Firefox-related issue. </blockquote>

Modified by Koreus

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