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Probable DNS issue

New Poster

Probable DNS issue

I am unable to reach a specific URL from our home.  We have tested it in every imaginable way with Comcast technical support. 

  • It is not an SSL3 exploit
  • We are able to reach other https:// locations such as American Express
  • IP V6 tests out at 10/10
  • The problem is not browser dependent - tested on Chrome, Firefox and Safari
  • It is not OS dependent - tested on ios and Windows
  • It is not device dependent - tested on 6 different devices
  • I CAN reach the site on my iPhone over Verizon
  • Is it down or is it me confirms that the site is up
  • I have spoken to the webmaster of the site.  They are not experiencing problems with anyone else - they are in a region that is mostly Time Warner

So, I have concluded it's a Comcast problem, and probably a DNS lookup issue with the site's IP address.  Comcast has been unable to help, and in most cases unable to even understand what I am talking about.  

 

Can anybody help?

Expert

Re: Probable DNS issue

What is the URL of the site ? Perhaps a trace route to the URL will reveal a clue ? If the URL / domain name resolves to a numerical IP address in the trace, then it is not a DNS problem.



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Contributor

Re: Probable DNS issue

Here's the best way to check, use another DNS provider.  I use Cloudflare.

On your PC:

  1. Click on the Start menu, then click on Control Panel.
  2. Click on Network and Internet.
  3. Click on Change Adapter Settings.
  4. Right click on the Wi-Fi network you are connected to, then click Properties.
  5. Select Internet Protocol Version 4 (or Version 6 if desired).
  6. Click Properties.
  7. Write down any existing DNS server entries for future reference.
  8. Click Use The Following DNS Server Addresses.
  9. Replace those addresses with the 1.1.1.1 DNS addresses:
    • For IPv4: 1.1.1.1 and 1.0.0.1
    • For IPv6: 2606:4700:4700::1111 and 2606:4700:4700::1001
  10. Click OK, then Close.
  11. Restart your browser.
  12. You’re all set! Your device now has faster, more private DNS servers
  13. Try the site you can't reach, it works, then, there you have it.
Expert

Re: Probable DNS issue

Actually, the trace route or ping method is a faster way to check if DNS is working correctly.



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New Poster

Re: Probable DNS issue

OK< this was helpful.  When I ping either the domain name or the ip address I get a timeout.  What does this indicate in terms of the root cause?  It's not an ip lookup issue as I had thought, because they are linked.  What's probably going on?

New Poster

Re: Probable DNS issue

OK< this was helpful.  When I ping either the domain name or the ip address I get a timeout.  What does this indicate in terms of the root cause?  It's not an ip lookup issue as I had thought, because they are linked.  What's probably going on?

New Poster

Re: Probable DNS issue

As you suspected, this is not a DNS issue.  When I ping either the domain name or the ip address I get a timeout.  What does this indicate in terms of the root cause?  It's not an ip lookup issue as I had thought, because they are linked.  What's probably going on?

Expert

Re: Probable DNS issue

Can you please post the full trace route output.



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New Poster

Re: Probable DNS issue

Definitely DNS. I had the same issue yesterday. Changed dns address and it was fixed.

Expert

Re: Probable DNS issue

FWIW, there is no guarantee that their issue has the exact same root cause as does your's. We need to see their trace route output.


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Expert

Re: Probable DNS issue

Well one thing to do is to open the Command Prompt in Windows or Terminal in MacOS and use the nslookup command. So 

 

nslookup www.comcast.com

Server: (DNS Server here)

Address: (DNS Server IP here)

Non-authoritative answer:

(DNS Lookup Info here)

 

The DNS server should match what you should be having, whether it's Comcast, CloudFlare,  OpenDNS, Google, Quad 9 or whatever. Anything else could indicate malware or intrusion. 

 

You can also clear your DNS cache if you suspect you're having problems there. 


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Expert

Re: Probable DNS issue

Yes but I'd like to see the trace to see if their WAN / public IP address is being blocked internally by the site.



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