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I am experiencing a strange behavior w.r.t DNS resolution when connected to certain WiFi networks. (only on iOS devices)

Issue is: Safari is able to resolve my domain name correctly but sometimes for almost 2 minutes it is not able to resolve and throws a page not found error. This happens say once in a couple of hours.

If I enter my ip address in Safari it works. At the same time the domain resolution works fine on android devices.

One Fix is: By default the DNS queries go to my ISP DNS, Now if i change the DNS settings to point to Google or OpenDNS or another popular DNS server the issue disappears. (but i can't use this solution for my usecase since i can't ask all my users to change their DNS settings).

The Android device is also in the same network and points to my ISP DNS, but for some reason with android the issue does not exist.

It seems to be problem with only Safari/iOS and my ISP DNS servers. Has someone faced a similar issue? Anything i can tryout?

P.S. I am using AWS instance and Route53 for DNS Service.

DevD
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  • Why the negative vote; kindly explain, so if clarity is the issue i will try to improve on my question and be more articulate. – DevD Mar 03 '16 at 06:57
  • Mouse over the down arrow; the popup says "*This question does not show any research effort; it is unclear or not useful*". Downvotes without comment may be presumed to be for at least one of those reasons. – MadHatter Mar 05 '16 at 09:52
  • @MadHatter Thanks for explaining I saw that but just could not believe that i have not done enough research. Last one week i have been browsing all over the web, testing my app umpteen times since the issue comes up randomly. Please guide me what other research i could do. Also i got two upvotes for the same question i posted on apple stackexchange, maybe because it seems to be a known issue with iOS. I have tried the same question on other groups as well after i failed with my research. Let me know if you need more info and i can provide more inputs on whatever research i did. – DevD Mar 05 '16 at 10:12
  • I found it really disappointing seeing the downvote. Either way i should be more concerned about getting my problem resolved than worring about the downvote. Thanks for the eye opener though! – DevD Mar 05 '16 at 10:12
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    You write that you have done a lot of research, which is great, **but you don't tell us about that in the original question**. This is frowned on, because it means that people waste time asking you to do things you've done already. When you write questions on SF in future, I would advise you to quickly but comprehensively **show** what you've tried already; it saves everyone else's time. Three cheers for you for deciding to worry less about downvotes, though: they're not worth losing sleep over! Finally, don't post a single question on multiple SE sites; that is forbidden. – MadHatter Mar 05 '16 at 10:17
  • @MadHatter I mentioned whatever i thought was relevant to the problem and what i had narrowed down to after failing with my research. I already mentioned the problem gets resolved by switching the DNS or it does not appear with android at all in the same network. So I can't help it if you ask me to check if i have a flaky Wifi or to test my firewall etc. I did not see the need to state the obvious. I do see however the problem may be something you may not have come across and so may find the question absurd or lame. – DevD Mar 05 '16 at 10:42
  • More over i accept that i am a novice and i need and want you to ask me to try out something i may not have thought off. Do let me know if you have any suggestions for me. I am really desperate to get this issue resolved – DevD Mar 05 '16 at 10:42
  • What exactly is the problem you are asking about here? Is it communication between DNS recursors hosted by the ISP and authoritative servers hosted by Route53, which is failing? If that's the case, then ask both of them why that is not working. – kasperd Mar 05 '16 at 16:15
  • @kasperd thanks; that's not the case; if that was the case then even other android devices would fail to resolve the domain. It's only iOS device which sometimes seems to give a negative result. This [link](http://www.saurik.com/id/3) - first section sums up what I am facing. I stumbled upon this today but it seems to be an old post. – DevD Mar 05 '16 at 17:25
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    @DevD In that case you need to grab some packet captures showing how the request and reply looks for devices that work as well as for devices that don't work. It would be useful to compare those to captures using a different DNS recursor. – kasperd Mar 05 '16 at 17:40
  • @kasperd thanks I will try that out. I will be doing this the first time. Do you have any reference links I could use. Thanks again! – DevD Mar 05 '16 at 18:14

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Safari is a browser, it just uses the underlying DNS machinery (in your C library, local cache on your machine, your WiFi router, any cache your ISP maintains, and finally the servers in the wide Internet). DNS is very redundant. So intermittent service most of the time means that something local is malfunctioning (bad WiFi connection, e.g. you move around into shadows; router is flaky; intermittent WLAN connection; ...).

To check network connectivity, there should be some form of ping command available. To debug DNS problems as such, the Unix tool is dig.

vonbrand
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  • Thanks for the response. I know it sounds silly but it is happening only for iOS on some of the wifi networks (not all networks). Android works fine. Also i do realize the problem is with DNS since with the ip-address it works fine. Changing DNS to Google also makes it work fine. I am just clueless at this point where to resolve what. If I search the web I see there are lot of wifi/dns connectivity issues on iOS 8 and 9. I can resolve my problem using those issues. but i can't ask my clients to follow the same steps. So i am in a fix right now. – DevD Mar 03 '16 at 06:54