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Unable to connect to screwfix.com (dns issue)

peter53
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Registered: ‎24-10-2022

Unable to connect to screwfix.com (dns issue)

‎24-10-2022 3:46 PM - edited ‎24-10-2022 3:47 PM

I have been having problems connecting to screwfix.com since Saturday.  This affects all devices in my home.  I can connect to the site successfully on mobile devices by disabling WiFi, and using mobile data instead.  I have been able to workaround the issue by overriding the DNS settings on each device, to use the server directly.  Other sites work fine, and I don't know of any other sites that are affected.

 

It seems that, due to the size of the query, TCP has to be used to perform the DNS lookup, but the router doesn't support DNS resolution via TCP.

 

Here's the nslookup output for the router:

 

$ nslookup www.screwfix.com 192.168.1.254
;; Truncated, retrying in TCP mode.
;; Connection to 192.168.1.254#53(192.168.1.254) for www.screwfix.com failed: connection refused.
;; Connection to 192.168.1.254#53(192.168.1.254) for www.screwfix.com failed: connection refused.
;; Connection to 192.168.1.254#53(192.168.1.254) for www.screwfix.com failed: connection refused.

 

 

Here's querying one of the DNS servers directly:

 

$ nslookup www.screwfix.com 212.159.6.10
;; Truncated, retrying in TCP mode.
Server:		212.159.6.10
Address:	212.159.6.10#53

Non-authoritative answer:
www.screwfix.com	canonical name = 1467314084df01340a26123dfe2baf36.yottaa.net.
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.123
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.87
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.125
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.178
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.18
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.126
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.122
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.90
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.181
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.91
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.92
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.23
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.179
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.89
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.93
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.177
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.124
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.180
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.182
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.88

 

 

Telnet to port 53 on the router:

 

$ telnet 192.168.1.254 53
Trying 192.168.1.254...
telnet: Unable to connect to remote host: Connection refused

 

 

And telnet to port 53 on the DNS server:

 

$ telnet 212.159.6.10 53
Trying 212.159.6.10...
Connected to 212.159.6.10.
Escape character is '^]'.
^]
telnet> Connection closed.

 

 

Interestingly, the lookup does not fallback to TCP with other DNS services.  Here's google DNS:

 

$ nslookup www.screwfix.com 8.8.8.8
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
www.screwfix.com	canonical name = 1467314084df01340a26123dfe2baf36.yottaa.net.
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.182
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.89
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.93
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.123
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.177
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.126
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.180
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.124
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.181
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.125
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.88
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.90
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.92
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.179
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.178
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.18
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.23
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.91
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.122
Name:	1467314084df01340a26123dfe2baf36.yottaa.net
Address: 165.254.56.87

 

 

Router details:

  • Plusnet Hub One
  • Software version 4.7.5.1.83.8.289.1.3 Last updated 15/11/21

 

Is there a way to resolve this?

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Rod
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Re: Unable to connect to screwfix.com (dns issue)

‎25-10-2022 8:51 PM

I don't have the answer, but I'm comforted to know that I'm not the only one experiencing this issue.

I can report that since Saturday I have been experiencing exactly the same problem. I too am unable to connect to screwfix.com via wifi from any device (they are all Android phones/tablets) through my Hub One router. I am also getting a message that there is a DNS issue. I have absolutely no problem connecting to any other website, and if I disable wifi on my phone and connect to the internet via 4g there no problem at all.

I've not been able to do the technical diagnosis as the original poster, but I suspect it could be the same cause.

Any resolution to this would be most welcome

Router details:

  • Plusnet Hub One
  • Software version 4.7.5.1.83.8.289.1.3 Last updated 15/11/21

 

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jgb
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Re: Unable to connect to screwfix.com (dns issue)

‎25-10-2022 9:52 PM - edited ‎25-10-2022 9:53 PM

I am using W11 and Chrome Version 106.0.5249.119 (Official Build) (64-bit) with the same router details as above with no problem. Have you tried clearing cache and cookies? 

Just updated Chrome to Version 107.0.5304.63 (Official Build) (64-bit) and still OK.

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bobpullen
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Re: Unable to connect to screwfix.com (dns issue)

‎25-10-2022 11:00 PM

What router are you using?

There have been discussions in the past about the fact that the Hub One does not handle TCP DNS requests gracefully.

Querying the router for DNS will add to the size of the reply that is returned, which explains why you don't see the issue when going direct.

Bob Pullen
Plusnet Product Team
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Rod
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 1:05 PM

Thank you jgb and bobpullen for your comments. First thing I did was to clear the cache and cookies on my Android devices, so it isn't that. On further investigation it transpires that a W11 PC connected to the Hub One via an ethernet cable is handling all DNS requests fine, as is an old W10 laptop connected via WiFi. It seems it is just the Android devices connected via wifi that are all struggling over just one particular website. 

It's interesting that the Hub One is known not to handle TCP DNS request gracefully, something I wan't aware of, so happy to accept this as the most likely explanation - I guess I've been lucky for quite some time until now.  As a workaround, I've changed the DNS settings on all three wifi Android devices to one of the free public DNS servers and all is now fine, so happy to leave it that way and regard that as a resolution.

Thank you all again, and especially bob for the info regarding the Hub One - I hope this has added a little more for the benefit of the original poster. 

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Mark61
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 2:22 PM

 I have exactly the same problem on my iPad, Samsung phone and laptop

while speaking to customer service this morning the site loaded as if by magic but has now stopped working again, not technically minded when it come to routers so not sure where to go from here

any easy solutions?

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alitster
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 6:47 PM

I've got exactly the same issue accessing the Screwfix website via my PlusNet Hub One.

I can't access it via my laptop or my Android phone. If I turn off wifi on my phone it works fine.

My issue is exactly the same as peter53 describes.

If the request is made against the PlusNet router, it just times out

lenny@ubuntu:~$ dig +noall +answer www.screwfix.com @192.168.1.254
;; connection timed out; no servers could be reached

However, if the request is made directly against one of the PlusNet DNS servers it works.

lenny@ubuntu:~$ dig +noall +answer www.screwfix.com @212.159.6.9
www.screwfix.com. 291 IN CNAME 1467314084df01340a26123dfe2baf36.yottaa.net.
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.91
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.18
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.88
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.124
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.179
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.92
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.181
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.90
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.123
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.93
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.125
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.23
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.126
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.177
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.122
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.87
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.178
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.89
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.180
1467314084df01340a26123dfe2baf36.yottaa.net. 291 IN A 165.254.56.182

That's a pretty big DNS response, usually there wouldn't be as many records as that returned.

Does the Hub One have a limitation in the size of the DNS response? Can't it cope with multiple UDP packets?Huh

Router details:

  • Plusnet Hub One
  • Software version 4.7.5.1.83.8.263 | Last updated 13/03/19
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bobpullen
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 7:06 PM

The problem will almost certainly be due to the size of the DNS response resulting in the DNS lookup falling back to TCP rather than UDP.

We've established previously that the Hub One (and some other routers) don't forward the retransmitted TCP packets upstream properly.

It gets a bit heavy in parts, but here's an example from the past.

Bob Pullen
Plusnet Product Team
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alitster
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 8:55 PM

When I ran a packet capture at the same time as running

lenny@ubuntu:~$ dig +noall +answer www.screwfix.com @212.159.6.9

I didn't see any TCP traffic at all on port 53, it's all UDP. So any TCP issues the router may have don't come into play.

www.screwfix.com is a CNAME record and resolves correctly by the Hub One if you only request that

lenny@ubuntu:~$ dig +noall +answer +stats CNAME www.screwfix.com @192.168.1.254
www.screwfix.com. 165 IN CNAME 1467314084df01340a26123dfe2baf36.yottaa.net.
;; Query time: 19 msec
;; SERVER: 192.168.1.254#53(192.168.1.254)
;; WHEN: Wed Oct 26 20:07:00 BST 2022
;; MSG SIZE rcvd: 102

and if you do a lookup on the returned CNAME record

lenny@ubuntu:~$ dig +noall +answer +stats 1467314084df01340a26123dfe2baf36.yottaa.net. @192.168.1.254
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.126
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.123
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.178
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.177
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.18
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.88
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.181
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.91
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.182
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.125
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.92
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.89
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.122
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.23
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.179
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.180
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.87
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.124
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.93
1467314084df01340a26123dfe2baf36.yottaa.net. 282 IN A 165.254.56.90
;; Query time: 87 msec
;; SERVER: 192.168.1.254#53(192.168.1.254)
;; WHEN: Wed Oct 26 20:08:52 BST 2022
;; MSG SIZE rcvd: 501

that then works. The received message size is only 501 bytes so fits easily into a single UDP packet.

This obviously isn't much use to a web browser, but it does prove that the Hub One can resolve it when it's under a certain size. When a single request is made to 212.159.6.9 it has a message size of 531 which the Hub One has issues with.

Any chance this issue can be escalated? Because as it stands we're unable to access the Screwfix website via PlusNet. 

 

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bobpullen
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Re: Unable to connect to screwfix.com (dns issue)

‎26-10-2022 10:10 PM - edited ‎26-10-2022 10:23 PM

@alitster - Interesting that you didn't see any TCP traffic, All still points to the issue being related to DNS responses that are above the 512 byte limit for a single UDP packet though.

There is a potential workaround in the post here (read the bit regarding 'Safeguard') that it may be worth you trying if this is causing a lot of inconvenience. The Safeguard DNS servers return fewer records which reduces the payload: -

 

$ dig www.screwfix.com @213.120.234.42

; <<>> DiG 9.11.5-P4-5.1+deb10u7-Debian <<>> www.screwfix.com @213.120.234.42
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27238
;; flags: qr rd ra; QUERY: 1, ANSWER: 21, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;www.screwfix.com.              IN      A

;; ANSWER SECTION:
www.screwfix.com.       66      IN      CNAME   1467314084df01340a26123dfe2baf36.yottaa.net.
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.87
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.124
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.125
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.182
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.92
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.123
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.122
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.180
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.178
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.177
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.18
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.23
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.93
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.126
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.90
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.179
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.88
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.181
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.91
1467314084df01340a26123dfe2baf36.yottaa.net. 67 IN A 165.254.56.89

;; Query time: 11 msec
;; SERVER: 213.120.234.42#53(213.120.234.42)
;; WHEN: Wed Oct 26 21:53:48 BST 2022
;; MSG SIZE  rcvd: 422

 

I will discuss the issue with the device vendor (ref: PNVDSL-134), however even in the event that we're looking at a different cause, any propsective fix isn't going to be a quick turnaround.

I'll also try and set some time aside this week to dig out a Hub One and grab some captures from the hub's network interfaces to see if I can see what's going on.

Your hub is running dated firmware by the way. This suggests it has probably lost contact with the management platform at some point.

Bob Pullen
Plusnet Product Team
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questuk01
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Re: Unable to connect to screwfix.com (dns issue)

‎28-10-2022 10:24 AM

Hi,

I am having exactly the same problem and test results as shown above.

I am running Linux and if i use Brave browser ( chrome based ) it fails, if I use Firefox it works ?

Look forward to a fix for this.

 

Thanks

Gaz

 

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Mark61
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Re: Unable to connect to screwfix.com (dns issue)

‎28-10-2022 12:16 PM

I have an old sky router upstairs that boosts the signal from the plusnet router, if I connect to the sky router I can get on Screwfix but still can’t get on if I connect to the plusnet router

 

 

 

 

 

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bobpullen
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Re: Unable to connect to screwfix.com (dns issue)

‎28-10-2022 1:17 PM

@Mark61 - when connected to the (working) Sky router, are you able to share the output from the following command run from a Windows CMD or Terminal prompt?

> nslookup www.screwfix.com

Bob Pullen
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alitster
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Re: Unable to connect to screwfix.com (dns issue)

‎28-10-2022 5:01 PM

@bobpullen wrote:
Your hub is running dated firmware by the way. This suggests it has probably lost contact with the management platform at some point.

@bobpullen how do I go about getting my Hub to reestablish connectivity with the management platform? @peter53 is on a later version and has the same issue. With reference to this my serial number ends '8838' if that helps?

I'd read the other day what you'd said about the Safeguard settings in that thread, but was reluctant to change to it as you'd also said it can't be reverted.

Screwfix was just an example of a site I'd found that didn't work due to the response being too large for the Hub One to cope, I'm sure there's probably other websites that are affected as well.

I'm quite comfortable with changing the DNS servers on my laptop, or using a different one for screwfix.com, but this would be a right nuisance for the average person. 

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colbee
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Registered: ‎06-04-2018

Re: Unable to connect to screwfix.com (dns issue)

‎28-10-2022 7:46 PM

Chiming in with the same issue as above.
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