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Robolovsky
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VM DNS servers slow to update or what?

As a long time virgin media customer and an IT professional I have noticed that the VM DNS servers seem to take a very long time to update compared to other providers. In my work environment I have access to Sky and Virgin broadband and whenever I have to change the DNS of a domain/website it always seems to be VM that takes the longest to propagate the change. Often the Sky servers will pick up the new DNS in an hour or two but many times it will take longer than the usual default maximum 24 hrs to propagate with Virgin.

I am wondering if there is a viable reason for this and if perhaps Virgin could take note and update their servers more frequently.

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Re: VM DNS servers slow to update or what?

BTW I wanted to add some further evidence, that this is not unique to Virgin Media.

Doing a quick Google for Sky DNS caching problem gives me this.

http://helpforum.sky.com/t5/Broadband/DNS-Caching-Problem-How-long-will-it-take-for-sky-broadband-DN...

I'm experiencing a strange DNS caching problem with Sky Broadband.

I'm a web developer and 5 days ago I transferred a website to a new hosting provider. When I try and access the website while connected to Sky broadband, it attempts to retrieve the website from the old hosting server. 

It doesn't appear to be a caching issue on my local machine because I've cleared the browser cache, tried different browsers and even flushed the dns locally. Further to this, if I temporarily change my local DNS settings so that it by-passes the Sky DNS and use the Google DNS instead, the website is displayed perfectly.

That was from 2016.  Now lets Try BT DNS Caching Problem instead

https://community.bt.com/t5/Connected-Devices-Other/BT-DNS-Refresh/td-p/770726

I'm a web deisgner, and I set up a client's website and changed the hosting from Godaddy to my own VPS hosting (www.powervps.com). I changed the NAMESERVERS on Monday at roughly 1.30pm, usually the changes take effect within minutes. It's Wednesday 10.12am and it still is showing the old page at the old hosting (Godaddy).

So when people try to tell me that this is uniquely a Virgin Media problem, I beg to differ.

The more likely scenario, is that in each case, the individuals listed in this post and the OP visited the site recently using their primary broadband provider. 

Depending on who exactly accesses the sites, if no one using one of the alternative DNS providers has visited the site in the last few days, then when testing to see if it works, the alternative DNS servers end up doing a fresh lookup which will of course pick up the new DNS results.

Tim

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Re: VM DNS servers slow to update or what?

Hi

The thing is, how much do you really know about Virgin's Public DNS servers?  For that matter how much do you really know about Sky's?

Because I don't have Sky broadband, I can't access Sky's DNS servers so I can't really comment on them.  However I can comment on DNS in general and also do a comparison between Virgin's DNS (194.168.4.100 and another such as Hurricane Electric's public DNS (74.82.42.42)

Public DNS Servers use Anycast addressing.

Now whichever provider you are using they all use Anycast addressing to connect you to the nearest recursive DNS server on the network.  However depending on how the provider sets up the Anycasting, means that for the same IP address, you MAY get the same DNS server every time, or you may get different DNS servers depending on which is available.

As an example, lets take a DNS lookup that can only produce one result and has a TTL of 1800 seconds.

Lets use Virgin's server (194.168.100.4) to do the same lookup multiple times.

 

C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 57900
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1800   IN      A       77.68.89.100

;; Query time: 50 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:29 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17822
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1796   IN      A       77.68.89.100

;; Query time: 12 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:33 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 8608
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1794   IN      A       77.68.89.100

;; Query time: 16 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:36 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47834
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1791   IN      A       77.68.89.100

;; Query time: 21 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:39 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 45296
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1788   IN      A       77.68.89.100

;; Query time: 11 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:42 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 34696
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1783   IN      A       77.68.89.100

;; Query time: 13 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:47 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18891
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1777   IN      A       77.68.89.100

;; Query time: 13 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:52 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @194.168.4.100 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @194.168.4.100 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47911
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1773   IN      A       77.68.89.100

;; Query time: 13 msec
;; SERVER: 194.168.4.100#53(194.168.4.100)
;; WHEN: Mon Nov 20 22:47:56 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68

If you check the list you'll see the TTL is counting down on each and every lookup.  Suggesting that the Anycast is always querying the same server.

 

Now lets do the same with Hurricane Electric's 

C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 56280
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1800   IN      A       77.68.89.100

;; Query time: 38 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:40:39 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 38545
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1794   IN      A       77.68.89.100

;; Query time: 17 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:40:45 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20020
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1800   IN      A       77.68.89.100

;; Query time: 39 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:40:49 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18208
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1785   IN      A       77.68.89.100

;; Query time: 107 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:40:55 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44839
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1791   IN      A       77.68.89.100

;; Query time: 20 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:40:59 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 28693
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1775   IN      A       77.68.89.100

;; Query time: 26 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:41:04 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68


C:\Users\timdu>dig @74.82.42.42 www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @74.82.42.42 www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 44307
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; ANSWER SECTION:
www.timothydutton.co.uk. 1780   IN      A       77.68.89.100

;; Query time: 20 msec
;; SERVER: 74.82.42.42#53(74.82.42.42)
;; WHEN: Mon Nov 20 22:41:09 GMT Standard Time 2017
;; MSG SIZE  rcvd: 68

Now if you check you'll see that while the overall trend is counting down, in the third lookup the TTL jumps back UP to 1800 and further down we see an increase in TTL from 1785 to 1791.

So what's happening?  TTL can only count down so we can postulate that in the Hurricane Electric case, the anycasting is actually querying more than one recursive DNS server, and that each server is caching the results separately.

Is this a good thing?

Yes and no.

Pro - You're likely to see a change in DNS more quickly.
Con - Because each server has it's own cache, then it's possible to end up with different results for the same DNS lookup until all previous cached entries have expired - In fact I've demonstrated this using OpenDNS who have a similar setup.

Why do some changes take 2 days to propogate?

My current domains DNS is actually managed by my own DNS server, with Glue records registered with nominet by my registrar

C:\Users\timdu>dig @nsa.nic.uk www.timothydutton.co.uk

; <<>> DiG 9.10.6 <<>> @nsa.nic.uk www.timothydutton.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39270
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.timothydutton.co.uk.       IN      A

;; AUTHORITY SECTION:
timothydutton.co.uk.    172800  IN      NS      ns2.box.timothydutton.co.uk.
timothydutton.co.uk.    172800  IN      NS      ns1.box.timothydutton.co.uk.

;; ADDITIONAL SECTION:
ns1.box.timothydutton.co.uk. 172800 IN  A       77.68.89.100
ns2.box.timothydutton.co.uk. 172800 IN  A       77.68.89.100

;; Query time: 24 msec
;; SERVER: 156.154.100.3#53(156.154.100.3)
;; WHEN: Mon Nov 20 23:15:11 GMT Standard Time 2017
;; MSG SIZE  rcvd: 124

The Glue Records not only provide the names of the servers, but also their IP addresses.

I have another domain, that doesn't need it's own Glue records, as the DNS is done by the above servers.

C:\Users\timdu>dig @nsa.nic.uk www.ravenstar68.co.uk

; <<>> DiG 9.10.6 <<>> @nsa.nic.uk www.ravenstar68.co.uk
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27121
;; flags: qr rd; QUERY: 1, ANSWER: 0, AUTHORITY: 2, ADDITIONAL: 3
;; WARNING: recursion requested but not available

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;www.ravenstar68.co.uk.         IN      A

;; AUTHORITY SECTION:
ravenstar68.co.uk.      172800  IN      NS      ns1.box.timothydutton.co.uk.
ravenstar68.co.uk.      172800  IN      NS      ns2.box.timothydutton.co.uk.

;; ADDITIONAL SECTION:
ns1.box.timothydutton.co.uk. 172800 IN  A       77.68.89.100
ns2.box.timothydutton.co.uk. 172800 IN  A       77.68.89.100

;; Query time: 20 msec
;; SERVER: 156.154.100.3#53(156.154.100.3)
;; WHEN: Mon Nov 20 23:24:32 GMT Standard Time 2017
;; MSG SIZE  rcvd: 136

Note though the TTL on these records 172800 seconds or 2 days.

Now when Virgin's or Sky's servers work their way through the hierarchy, they will cache the details of the Authoritative nameservers in order to avoid having to keep looking them up.  So if I visit www.ravenstar68.co.uk using Virgin's public DNS and then shortly afterwards change registrar, then it will take two days before those changes are picked up.

Now if I do the same thing using HE.net's DNS then if I get a different server, the DNS channges appear to have successfully propogated,  BUT every so often I will keep getting the old DNS lookups instead when I hit the server that previously cached the entries, this will continue until the 2 day TTL has expired.

Tim

 

 

 

________________________________________


Only use Helpful answer if your problems been solved.

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Superuser
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Message 3 of 4
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Helpful Answer

Re: VM DNS servers slow to update or what?

BTW I wanted to add some further evidence, that this is not unique to Virgin Media.

Doing a quick Google for Sky DNS caching problem gives me this.

http://helpforum.sky.com/t5/Broadband/DNS-Caching-Problem-How-long-will-it-take-for-sky-broadband-DN...

I'm experiencing a strange DNS caching problem with Sky Broadband.

I'm a web developer and 5 days ago I transferred a website to a new hosting provider. When I try and access the website while connected to Sky broadband, it attempts to retrieve the website from the old hosting server. 

It doesn't appear to be a caching issue on my local machine because I've cleared the browser cache, tried different browsers and even flushed the dns locally. Further to this, if I temporarily change my local DNS settings so that it by-passes the Sky DNS and use the Google DNS instead, the website is displayed perfectly.

That was from 2016.  Now lets Try BT DNS Caching Problem instead

https://community.bt.com/t5/Connected-Devices-Other/BT-DNS-Refresh/td-p/770726

I'm a web deisgner, and I set up a client's website and changed the hosting from Godaddy to my own VPS hosting (www.powervps.com). I changed the NAMESERVERS on Monday at roughly 1.30pm, usually the changes take effect within minutes. It's Wednesday 10.12am and it still is showing the old page at the old hosting (Godaddy).

So when people try to tell me that this is uniquely a Virgin Media problem, I beg to differ.

The more likely scenario, is that in each case, the individuals listed in this post and the OP visited the site recently using their primary broadband provider. 

Depending on who exactly accesses the sites, if no one using one of the alternative DNS providers has visited the site in the last few days, then when testing to see if it works, the alternative DNS servers end up doing a fresh lookup which will of course pick up the new DNS results.

Tim

________________________________________


Only use Helpful answer if your problems been solved.

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Robolovsky
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Re: VM DNS servers slow to update or what?

Many thanks for this ravenstar68. It does go a long way to explaining the true situation.
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