[Merged] DNS (ARP) dropping frequently issue on 20M service

j-a · 13-08-2008, 14:51

Hello, I'm a new member specifically to ask this question

I have a DrayTek dual wan router (Vigor 2930) connected to Virgin cable and BT adsl; I bought this to eleviate the problem of constantly getting errors on DNS that required me to re-boot the router. It switches to BT (slow) if the cable (fast) goes down - it uses ARP testing to "see" the failure.
Trouble is some days (not every day) it keeps going down all day long every few minutes for a few minutes; this causes problems switching isp in the middle of a remote session or a download.
Is this a know problem and any has anyone got any suggestions? Thanks!!

moaningmags · 13-08-2008, 14:52

What are your dns servers?

Seem to be issues with
194.168.4.100
194.168.8.100

j-a · 13-08-2008, 15:08

Wow, quick response thanks.
I'm using OpenDNS servers on 208.67.222.222 & 208.67.220.220. But I also had exactly the same problems using the DNS servers from the DHCP.
I should point out that the issue existed long before I had the DrayTek but I couldn't pin it down until recently when I bought this new router - now I know exactly what the problem is.

chickendippers · 13-08-2008, 15:12

I've used OpenDNS for over a year and can't say I've ever noticed a problem.

altis · 13-08-2008, 15:16

You're not the only one with DNS issues. I'm currently using the VM ones (194.168...) but I have the same probs with OpenDNS. It's been happening for weeks now but has been noticeably worse since an enforced computer upgrade about 4 weeks ago.

It seems to be worse with odd subdomains like all the various different ones that ebay uses.

Broken Hope · 13-08-2008, 16:26

For the past week or so I have been having issues with sites timing out, and I mean all sites not just the odd one or two and today when it happened I tried to run a tracert and got the following back

Unable to resolve target system name www.virginmedia.com

This problem has been happening every day for the past week, it only lasts for around 10 minutes a day at random times and then clears up on it's own.

gtucker · 13-08-2008, 16:43

Use Opendns instead. I find them a lot more reliable

http://www.opendns.com/

j-a · 13-08-2008, 17:06

I use OpenDNS and have identical problems. I posted a question about this myself today, it seems that its a more general issue.
How do I join threads is that a moderator thing in this forum?

Cobbydaler · 13-08-2008, 17:47

Quote:

Originally Posted by j-a

I use OpenDNS and have identical problems. I posted a question about this myself today, it seems that its a more general issue.
How do I join threads is that a moderator thing in this forum?

Threads merged

Axegrinder · 13-08-2008, 18:19

That is strange.

That might be why my internet is dropping intermittently, (see thread in networking)

I am using OpenDNS by the way.

flashpaul · 13-08-2008, 21:04

I have been seeing intermittent drop outs , thought it was a faulty network card it worked fine for a week until today

altis · 13-08-2008, 21:10

This is easy to identify if you use Firefox as your internet browser. At the bottom is a status line that tells you how it's progressing with rendering each page. Most of the time when you look it just says 'Done' because it's finished rendering. However, when it's waiting for a DNS request you'll see, for example, 'Looking up cableforum.co.uk'. If the DNS request fails then that's what you see for ages until it finally gives up and says it can't find the page.

This may just be a packet loss issue rather than an actual DNS issue. This is because this service uses UDP datagrams. Unlike TCP, this has no means of error recovery. If a packet gets lost then it's up to the application to recover - or not!

http://en.wikipedia.org/wiki/Domain_Name_System
http://en.wikipedia.org/wiki/User_Datagram_Protocol

Axegrinder · 13-08-2008, 21:16

Thats what keeps happening to me.

Suddenly Firefox is "Looking up" everything.

j-a · 14-08-2008, 00:08

A bit more information about my issue.
I actually use my broadband to connect via a Citrix session to a remote desktop and I also use a VPN on occasions; I was suffering with constant session dropouts, I've had 3 engineer visits with no cure, so I invested in the dual wan router to provide failover to the (slow but sure) BT adsl line.

The router decides when WAN1 has failed by making occasional ARP lookups like it was doing DNS work, if the lookup fails it switches to WAN2.
Now I have this kit in place I can see what was always going wrong but which I wasn't able to pin down, the dropouts are caused by the ARP/DNS services stopping for a few minutes (typically 3 or 4 mins) then recovering. If I were to reboot the cable modem during this time the ARP/DNS comes back instantly. During this dropout period all the actual ip traffic continues fine with no noticable disruption.

Does this scenario give any deeper insight of my issue, does it seem familiar to anyone? I'd really like to get this fixed as I'm teetering on the brink of cancelling my expensive 20Mb contract because the dropouts are so frustrating.

altis · 14-08-2008, 10:06

Quote:

Originally Posted by j-a

... the dropouts are caused by the ARP/DNS services stopping for a few minutes (typically 3 or 4 mins) then recovering. If I were to reboot the cable modem during this time the ARP/DNS comes back instantly. ...

I wonder whether the 3-4 minute delay is actually created by your router as it times-out on WAN1 and tries not to use it again for this period.

Still, that's useful information that you've provided.

I've the feeling that this problem is something to do with datagrams rather than the DNS service itself. This is because I've seen the same issues no matter if I use OpenDNS or VM's own servers.

The problem did seem to be worse after 5pm when all the kids got home from school. However, it is eased if I used the proxy server at renf-cache-9.server.ntli.net.

Some people see it quite consistently whilst others do not. I only noticed it seriously after I upgraded my computer. I never seem to have any problems with Mrs A's machine which is much slower but uses the same connection.

I'm wondering if somehow this is something to do with the timing between packets. Perhaps my machine can now send out back-to-back DNS datagrams and some later ones are getting lost.