Does anyone know how to prevent DNS caching on iOS? My DNS cache keeps getting fouled up and it causes all sorts of issues that affect:

  • Population of the bonjour pane in the VNC app
  • Detection of airplay speakers connected to airport expresses
  • Detection of airplay screen mirroring devices like an apple TV
  • Detection and control of accessories setup in the Home app
  • Detection of shared iTunes libraries in the iTunes Remote App
  • Resolution of .local addresses for things like:
    • my eyetv media server
    • sshing via the terminus app
    • connecting to vlc streams
    • web pages on my local network from my laptop

I can temporarily flush the DNS cache by turning airplane mode on and back off, which fixes the all of above issues, but that only lasts for a little while. The next time I try to access any of these things, it again doesn't work.

I have tried "Reset all settings" and in the past, I have done a clean install of iOS 11. Neither of those methods permanently fixed this issue. The temporary fix of turning airplane mode on and back off was a tolerable solution, but I just recently setup the Home app and am using Siri to control smart plugs, my TV, etc. - and having to turn airplane mode on and off anytime I want to tell Siri to turn something on or off kind of defeats the purpose.

My iPad Mini does not have this issue, nor does any of my 5 computers (4 macs and a raspberry pi). Both mine and my wife's iPhone 6s has the same issue and it's been an issue since we got them, years ago.

It would even help if there was a way to inspect the DNS cache to see what's happening - like if it's a particular device/setting that's mucking up the cache on my iPhone.

Apple wants me to do a clean install of iOS 12, but given my experience with the iOS 11 update and what I've read about battery issues with iOS 12 on an iPhone 6s, I'm very reluctant to do that. I'd much rather know specifically what the problem is and find a less drastic fix.

  • You haven't really explained why you think this is a problem with the DNS cache? Can you elaborate? - Sounds more like a Bonjour issue of sorts. As regards to iOS 12, I haven't really heard about problems here - most, if not all, report that it fixes problems and improves performance. – jksoegaard Mar 18 at 17:52
  • Also please specify how your devices are connected to the network. I guess the iPhones connect to a WiFi router? - Are your computers also connected via WiFi, or via cables? - To the same router? – jksoegaard Mar 18 at 17:53
  • I can't really know it's the DNS cache because I don't have access to the cache to confirm a misconfig. It's a hunch based on a number of factors, including the fact that turning airplane mode on/off is documented to flush the DNS cache here (and elsewhere): buffered.com/tutorials/how-to-flush-dns-cache and that resolution of .local domains is affected (only on the iPhones). I in fact suspect that bonjour is the ultimate culprit, but that the mechanism has to do with it's inappropriate triggering of improper DNS cache values. I have 1 wired/1 wifi & connecting to both is affected. – hepcat72 Mar 18 at 18:02
  • You know, is there a diagnostic tool I can use to see the route the phone is taking when it tries to resolve a .local domain, like what IP it's trying to access? Traceroute or something? I'm not a network expert. Like, is there a tool where I can enter a .local address and watch to see what IP it tries to use? – hepcat72 Mar 18 at 18:06
  • The iNetTools app has a traceroute function. I'm definitely going to try that when I get home! – hepcat72 Mar 18 at 18:07

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