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I'm hoping one of you guys can help me. My ISP in the UK (Virgin Media) is caching DNS settings.

I change the name servers of any domain and / or DNS settings. If I use whatsmydns.net I can see that the settings have fully propagated within the usual time of around 6 hours. I can see the new hosting in this case on my phone if I turn off wi-fi but if I connect through my home wi-fi and use my ISP I see the old website. This seems to persist for around 4 days.

If I make changes to the website then I can see these changes I just can't see the refreshed DNS.

Has anyone else experienced this? Its really annoying for me as I change DNS settings quite often and I'm having to continually check on my phone to see the updated results of my changes.

Ricky55
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1 Answers1

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As a fellow Virgin Media (UK) user I can attest to their poor DNS management. ON the other hand, DNS caching is very common; instantaneous DNS configuration does not exist anywhere (that is, unless you have an intranet with an internal name server). A couple of hours is a typical delay in DNS caches.

On the other hand, there is absolutely nothing that forces you to use your ISPs DNS server (actually, some ISPs do give you equipment that is completely locked and disallow UDP packets through, but that is not the case with Virgin Media). You should definitely use a nameserver that is trusted by you, not imposed by your ISP.

The nameserver that I'll use for this example is Google's nameserver (8.8.8.8 and 8.8.4.4). You have two options of setting it:

Configure router DNS

If your router has configuration options for DNS use them, and set them to 8.8.8.8 and 8.8.4.4. Your router is what provides all DHCP parameters to your machines and the DNS servers are within these parameters.

If, like me, you're using the latest Virgin Media Super Hub, then you cannot change the DNS configuration of the router. One way to get around it is to configure the VM Super Hub as a modem and use another router as the effective router. That requires you to have/buy an extra router though.

Configure the DNS resolver on your machine

If you cannot reconfigure what nameservers the router presents to you, you can instead configure what nameservers your machine will use. Your question is borderline off-topic for the U&L website since it does not asks explicitly about anything UNIX related. Yet, form the fact that we are on U&L, I'll assume you are on a *nix machine.

The DNS resolver configuration is in the /etc/resolv.conf file, the file needs to be edited as follows:

nameserver 8.8.8.8
nameserver 8.8.4.4

Yet, if you just edit that file, that configuration will be overwritten by your DCHP service on any modern *nix system. You also need to configure your DHCP service to not update DNS information when it retrieves it from the router. The most common DHCP service today is provided by the dhcpcd package (I believe).

To configure dhcpcd to ignore the DNS information it gets from the router (and not overwrite resolv.conf) you need to ensure that the file /etc/dhcpcd.conf has no uncommented line as:

option domain_name_servers

Note that several options can be set on a single line inside /etc/dhcpcd.conf. You need to make sure that domain_name_servers is not present in any of the lines starting with option.

grochmal
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  • I realised I was bordering off topic so thanks for answering in such a comprehensive manner. I'm still learning but I do understand your answer. I'm actually running OS X. I too have the latest Virgin router so it looks like I'll have to try the second of your solutions. Out of interest do you know how long the Virgin DNS does take to refresh? It still persists way beyond all the servers listed on whatsmydns. – Ricky55 Jun 27 '16 at 08:25
  • Sorted now, on my Windows machine just used googles servers 8.8.8.8 works a treat. Thanks man I didn't know you could do this. – Ricky55 Jun 28 '16 at 14:36
  • @Ricky55 My evaluation of Virgin Media DNS caching is purely a guesstimate. Although, I have an astonishing example in which I added a subdomain around November last year and they haven't figured it out yet. You should have a look at the command dig <domain.name> which gives you a lot of useful information about DNS queries. – grochmal Jun 28 '16 at 16:35