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DNS issue?

sullyc
Newbie
Posts: 8
Registered: 20-02-2009

DNS issue?

I'm getting no joy from Plusnet support so trying here as it's been a week now. Anywhere else I could be looking?
Summary:
* I had a problem in Jan(?) for about a week where I could access certain web sites but not others
* Also sometimes the router would seemingly connect DSL fine on reboot but there would be only local access
* This issue 'magically went away' so I let it slide with Plusnet support
* It's been back for about a week now
* Not trusting my cheap router I bought another but the symptoms are exactly the same
Following some guidance I found on the Plusnet groups I tried the Open DNS servers to see if this improved matters. It did but but still issues with lots of domains. Here' what has become my test sample Sad
ADSL Accessibility Results 09.10 20/02/09
email (outlook – work and home account) Y 100% up
work intranet (teamsite.propona.co.uk) Y 100%
http://mail4.hostinguk.net (work webmail) N (Plusnet) => Work if I use Open DNS servers, not if I use Plusnet’s
http://www.plus.net
Y 100%
http://www.google.co.uk
N (plusnet) => Work if I use Open DNS servers, not if I use Plusnet’s
http://www.dabs.com
Y 100%
http://www.ebuyer.co.uk
Y 100%
http://www.facebook.com
N (plusnet) missing images (images from different IP?) Work if I use Open DNS servers, not if I use Plusnet’s.
http://www.propona.co.uk
N (Plusnet) => Work if I use Open DNS servers, not if I use Plusnet’s
http://www.timesonline.co.uk
X Was OK yesterday, not today. Why?
http://www.bbc.co.uk
X 0%
http://www.bmibaby.co.uk
X 0%
http://www.ebay.co.uk
X 0%
Help please!
Plusnet have asked me to do the standard unplugging everything (how can this help with an apparent DNS issue?) and have also asked for a tracert (copied below) but that was 2 days ago now ...
Microsoft Windows [Version 6.0.6001]
Copyright (c) 2006 Microsoft Corporation. All rights reserved.
C:\Users\chris.sully.PROPONA>tracert 212.58.227.73
Tracing route to 212.58.227.73 over a maximum of 30 hops
1 1 ms <1 ms 1 ms 192.168.0.1
2 39 ms 38 ms 38 ms lo0-plusnet.pte-ag1.plus.net [195.166.128.64]
3 39 ms 37 ms 38 ms ge0-0-0-403.pte-gw2.plus.net [84.92.4.2]
4 * * * Request timed out.
5 * * * Request timed out.
6 ^C
C:\Users\chris.sully.PROPONA>tracert http://www.bbc.co.uk
Tracing route to http://www.bbc.net.uk [212.58.253.67]
over a maximum of 30 hops:
1 1 ms 1 ms <1 ms 192.168.0.1
2 42 ms 38 ms 38 ms lo0-plusnet.pte-ag1.plus.net [195.166.128.64]
3 37 ms 38 ms 38 ms ge0-0-0-403.pte-gw2.plus.net [84.92.4.2]
4 * * * Request timed out.
5 * * * Request timed out.
6 ^C
C:\Users\chris.sully.PROPONA>
Ta.
Chris.
21 REPLIES
dieselglider
Grafter
Posts: 78
Registered: 27-11-2007

Re: DNS issue?

Has no one asked you to try changing the MTU yet?  That can give such problems.
paulby
Grafter
Posts: 1,619
Registered: 26-07-2007

Re: DNS issue?

Have you tried specifying the DNS server used directly on your PC rather than allowing your router to handle DNS?  (Router proxying of DNS has been known to cause issues!)
Assuming you're running XP go to Control Panel>Network Connections and right click on your connection.  Select properties then highlight TCP/IP in the box and select Properties  On the page that follows, select "Use the following DNS server addreses" and enter either PNs DNS servers or OpenDNS's. (Some people enter one PN server and one OpenDNS.)
PN's servers are:
212.159.13.49 and 213.159.13.50  (from this page)
OpenDNS's are:
208.67.222.222 and 208.67.220.220
Also, as suggested by dieselglider, you should try changing your MTU (1430 is often suggested as a god value).  You should do this on the PC and also make sure that your router's MTU is set to the same or a higher value than the PC's.
This page will give you some good advice and help on how to change your MTU.
sullyc
Newbie
Posts: 8
Registered: 20-02-2009

Re: DNS issue?

Thanks for the quick responses.
Yes, MTU settings tried with no success (I left out a few of the hoops jumped through for simplicity) but I'll fill in the gaps now:
I had a cheap ebuyer (Plexus) WBR-T2 V 0.2 (=Tenda TWL548D) which Plusnet support pointed out had known MTU issues. I tried setting windows MTU setting to 1400 (netsh interface ipv4 set subinterface "Local Area Connection" mtu=1400 store=persistent) as recommended for this router but this did not improve the situation. The Plexus did not allow you to set the router MTU setting easily.
For the new router (Netgear Wireless-N Modem Router DGN2000) I've reset both router and windows (Vista by the way ) at (the standard?) 1500 to hopefully eliminate this as a possible source. I could try resetting both to 1430 and see if that makes a difference?
I'll give the PC specified DNS a whirl - I'll go try and find the equivalent on Vista now.
Thanks again - this is driving me crazy at the moment.
paulby
Grafter
Posts: 1,619
Registered: 26-07-2007

Re: DNS issue?

As you're running Vista you'll need to make sure that you specify the DNS under TCP/IP V4.  You should also untick the box against version 6 to disable it (it's been known to cause problems having both V4 and V6 enabled). 
For Vista you need to go to Control Panel>Network & Sharing Center and select "Manage Network Connections" from the menu on the right.  The rest is then the same as for XP.
sullyc
Newbie
Posts: 8
Registered: 20-02-2009

Re: DNS issue?

Thanks. No improvement unfortunately but I'll detail what I did in case you spot any errors/ issues:
* Specified one PN server and one OpenDNS server under v4
* disabled v6
* flushed the DNS - still couldn't browse to problem sites (ebay and bbc)
* just in case, restarted the m/c - still no joy
Missing anything?
I'll try setting MTU of both windows and router to 1430 next.
paulby
Grafter
Posts: 1,619
Registered: 26-07-2007

Re: DNS issue?

Looks OK to me!
It's worth trying the MTU change (follow the instructions on Kitz site as you need to use the command prompt to change MTU in Vista - you can't use Dr.TCP - see here).
Highlighted
sullyc
Newbie
Posts: 8
Registered: 20-02-2009

Re: DNS issue?

Tried - no joy. I actually went with 1458 as this seems to be what my netgear wanted to set the MTU at - it had reset from the 1500 I had manually configured it to previously when I last tried using its 'clever' set up wizard - I figured it probably knows better than me if it can pick up all my other connection details automaticllyWink I set windows at 1458 to match. Still the same issues.
This may be a different issue but when I reset the computer a couple times back I lost internet connectivity completely - hence why I tried the setup wizard again in the vain hope it would restore some form of service. It did.
I suppose I had better actually do some work today but thanks for the help and any other suggestions very welcome.
paulby
Grafter
Posts: 1,619
Registered: 26-07-2007

Re: DNS issue?

It's worth trying 1400 on the PC.  The ping results from my connection (using -l to set the packet size and -f to set do not fragment) suggest that bbc.co.uk needs an MTU of 1400!
You don't have to change the router so long as it's a higher value than the PC.
C:\Documents and Settings\Paul>ping bbc.co.uk -l 1430 -f
Pinging bbc.co.uk [212.58.224.138] with 1430 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Ping statistics for 212.58.224.138:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
C:\Documents and Settings\Paul>ping bbc.co.uk -l 1400 -f
Pinging bbc.co.uk [212.58.224.138] with 1400 bytes of data:
Reply from 212.58.224.138: bytes=1400 time=68ms TTL=122
Reply from 212.58.224.138: bytes=1400 time=61ms TTL=122
Reply from 212.58.224.138: bytes=1400 time=67ms TTL=122
Reply from 212.58.224.138: bytes=1400 time=68ms TTL=122
Ping statistics for 212.58.224.138:
    Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
    Minimum = 61ms, Maximum = 68ms, Average = 66ms
sullyc
Newbie
Posts: 8
Registered: 20-02-2009

Re: DNS issue?

No joy again I'm afraid (actually I think I'd tried this before).
* Set computer MTU to 1400
* Restarted
* Still no access to bbc.co.uk
As the issue is with so many sites (estimated 30% of those tried maybe) is the issue likely to be local, particularly given the fact this issues has 'just appeared' twice now without any local hardware or software changes (as far as I am aware anyway). Last time it disappeared again after about a week so I'm hoping it is going again anytime nowWink If it does, this time I shall carry on chasing plusnet for a reason.
It's getting to the stage now I'm considering switching to a complete different physical line - the NTL/ Virgin 2nd phone line I have ... That, and the other Plusnet suggestion of callign BT out to check the line. Though quite how an IP access issue can be related to the line itself is beyond my limited knowledge of telecoms.
Thanks again.
dieselglider
Grafter
Posts: 78
Registered: 27-11-2007

Re: DNS issue?

@ Paul03
Taken from the Kitz site;
Quote
The ping command (for windows users) you need to use is:
    ping -f -l [packet size] [www.bbc.co.uk]    where [packet size] is the size of the packet.
Start at say 1472, and work your way down until you get a responsive ping from the highest number you can.
More information about the PING command
MTU ping

"Packet needs to be fragmented but DF not set" indicates that the packet size is too large.
In the example above it shows that my highest responsive ping is 1402.
From this we need to add on 28 to get the maximum MTU figure.

(28 being the header size for IP + ICMP)
Do not go above 1472. (1472 + 28 = 1500 MTU) since 1500 is the maximum MTU.

The reason why yours isn't resolving at 1430 may be because your MTU is at 1430 already?  In which case inserting 1430 in the ping test actually equals 1458, higher than the pc will transmit at.  The pc needs to be set at 1500 to test.  I think I'm correct.  Undecided
paulby
Grafter
Posts: 1,619
Registered: 26-07-2007

Re: DNS issue?

You're absolutely right!
(I totally forgot about adding the 28 to MSS and to reset my PC to 1500  Sad  )
@sullyc
Sorry about the bit of a bum steer but at least we now know it's highly unlikely to be an MTU issue.
It's not looking like a DNS issue either TBH (unless there's something local to your PC or router) as you're getting the same problems with PN's and OpenDNS's servers.
One other thing springs to mind though - have you got a third party firewall installed (Norton, Zone Alarm etc.)?  If so, have you disabled the Windows firewall? (It's a bad idea to run two firewalls as they'll conflict with each other.) 
Have you also tried disabling your firewall temporarily to rule out any firewall issues? (It's unlikely to be this but worth ruling out anyway.)
sullyc
Newbie
Posts: 8
Registered: 20-02-2009

Re: DNS issue?

I have only windows firewall running - I could look in that direction but I've just tried the following:
if I ping the sites I can't access via http from the router diagnostics page (to eliminate the computer and its software from the equation?) there is 100% loss:
bbc.co.uk (212.58.224.13Cool
PING 212.58.224.138 (212.58.224.13Cool: 56 data bytes
--- 212.58.224.138 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

66.135.221.12 (ebay.co.uk)
PING 66.135.221.12 (66.135.221.12): 56 data bytes
--- 66.135.221.12 ping statistics ---
4 packets transmitted, 0 packets received, 100% packet loss

Also, exactly the  same issues are occuring on both PCs on the (wired) LAN here.
I can give the firewall option a go though if you still think it worth a try?
Plusnet Alumni (retired) _CN_
Plusnet Alumni (retired)
Posts: 385
Registered: 11-06-2007

Re: DNS issue?

Give traceroute a go also, show if your getting off the local network.
Plusnet Alumni (retired) _CN_
Plusnet Alumni (retired)
Posts: 385
Registered: 11-06-2007

Re: DNS issue?

Hi
Took a quick look at your account and think your issue is because there are two active sessions with your username, and as you have a static IP there are routing issues. Can you change your password, post back here and I'll kill the other session.  Do you know why someone might have your login details?
Carl