why do OS/X apps fail when DNS is working fine?

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Scenario: browser stops working

A description short of detail: what browser, and please define 'stops working'.

Also, what apps (other than browsers) do you think should be using DNS?

How are you connecting & what are your DNS settings?

What DNS settings are in your Router?

Make a New Location, Using network locations in Mac OS X ...

http://support.apple.com/kb/HT2712

10.5, 10.6, 10.7 & 10.8…

System Preferences>Network, top of window>Locations>Edit Locations, little plus icon, give it a name.

10.5.x/10.6.x/10.7.x/10.8.x instructions...

System Preferences>Network, click on the little gear at the bottom next to the + & - icons, (unlock lock first if locked), choose Set Service Order.

The interface that connects to the Internet should be dragged to the top of the list.

If using Wifi/Airport...

Instead of joining your Network from the list, click the WiFi icon at the top, and click join other network. Fill in everything as needed.

For 10.5/10.6/10.7/10.8, System Preferences>Network, unlock the lock if need be, highlight the Interface you use to connect to Internet, click on the advanced button, click on the DNS tab, click on the little plus icon, then add these numbers...

208.67.222.222

208.67.220.220

(There may be better or faster DNS numbers in your area, but these should be a good test).

Click OK.

As a guess, there's a bad DNS server in your ISP's DNS server pool.

8.8.8.8 and 8.8.4.4 are Google's open-access DNS servers. Easier to remember than the ones BDAqua suggested, but the same request to try a different pool of DNS servers.

FWIW, dig bypasses local DNS caching and goes to the default or the specified DNS servers, where ping uses local DNS caches

Since this is a web browser that's involved and other services are apparently working, some other HTTP- or HTTPS-level component may well be in play here, such as a network filter, network security monitor, a firewall, or a network proxy server. You'll have to check the local settings, and see where the "stops working" is arising.

So, is it using a Proxy Server in Sys Prefs>Sharing?

random42 wrote:

I'm sitting on a segment of a corporate network, DNS isn't the problem - it still works.

Connectivity isn't the problem - it still works.

The issue is that OS/X obviously uses something other than DNS to do name lookups - which doesn't always work, but no one seems to have a clue what that is.

HUP'ing the usual suspects (mDNSResonder) and clearing caches makes no difference.

Obviously DNS is the problem or else you wouldn't have posted anything. What happens when you use a 3rd party DNS like OpenDNS or Google? Does the problem go away? We are all using OS X too and not having any problems. Your problems must come from whatever is different about your network. Corporate networks often do funky things to network setttings and are rarely tested on anything but Windows. You seem pretty handy with UNIX, so use the scutil command to poke around at what your dynamic network configuration actually looks like.

If a WINS server is pushing multiple search domains in the DHCP setup, OS X will not always pick them up and this can cause problems.

scutil --dns will show you the current setup of the resolver cache, including the resolvers established for DHCP promulgated search domains.

From Snow Leopard (or maybe Lion) onwards, all "native" DNS queries are made through the mDNSResponder Daemon, in much the same way that launchd acts as a "super-listener" for all active server ports coming inbound.

If HUPing mDNSResponder is having no effect, then the daemon is working correctly, and it must be a problem in the configuration - again, something most likely caused by the DHCP setup when joining your network.

random42: Have you found out any additional details on this matter?

I've had the same thing happen a number of times, same symptoms although the problem is noticed when using Mail. I agree with what you say, it's like OS X's internal DNS infrastructure "hangs", even though DNS *is* fine - DNS lookups from the machine, using `host` etc, works fine. It's something inside OS X that stops working, and I haven't found a way to kick it live again either, nothing short of a reboot helps AFAIK at this point in time.

It's been happening on both 10.8 and 10.9 for me. It might have been on 10.6 as well, I don't remember.

EDIT: I'm gonna try the solution proposed in https://apple.stackexchange.com/questions/26616/dns-not-resolving-on-mac-os next time it happens.

i have been experiencing something similar to the issues being observed in this post.

I have done more troubleshooting and here are the details of our situation

User - Macbook pro 13" 10.9.4. Mavericks

Enterprise wireless - Aruba Wireless

[symptom] User cant print -

[reason] he cant print because OSX cant properly ask for the DNS to IP query.

[sympton] User believes DNS Server is having issues

[reason] DNS does not answer because when we saw his problem... and ran TCPdump in the back... we can clearly see the OS does not append the suffix

[sympton] User shuts down wireless and restarts it... issue goes away

[reason] Stack gets restarted and whatever process was stale... it is back up and running post process restarted.

Observation 1

This issue appears to surface randomly when the user laptop goes to sleep... not always

Observation 2

User is always wireless connecting to the network

Observation 3

User tries to print to a network printer... different subnet than wireless

Hypothesis 1

Issue lies due to conflict between DNS and Bonjour. Something gets corrupted in DNS and Bonjour takes over. however Bonjour does not work outside the subnet it is in as it uses Multicast.

DNS goes out since the workstation goes to sleep losing its ip address.

Corporate DNS uses LDAP authentication

Bonjour is zero configuration and could stay running if configured.

therefore IP queries to device work. ip queries to fully qualified name work. making the OSX query the name by common name does not work.

not sure how close I am to solving my issue

Please start your own thread, as this question is headed in a different direction from the base question, and some of the details here are already very different from the base question.

OS X uses a common resolver for DNS and mDNS.

Could you elaborate on "Corporate DNS uses LDAP authentication"?

Potential workaround: use the FQDN for the printer.