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Some of my coworkers are having troubles on their Macs - DNS resolution does not work under Mac OS. They're running Snow Leopard 10.6.8. They can use DNS in a Windows 7 virtual machine (VMware Fusion 3.1.3) running under OS X. The computers are 15" MacBook Pros, early 2011 model.

Things they've tried that have not worked:

  • turning airport on/off
  • rebooting
  • using wired connection instead wifi
  • deleting connection credentials and adding it again
  • turning off Mac firewall
  • using fixed static IP
  • manually setting DNS servers
  • restarting mDNSResponder
  • the fixes from this other question

EDIT response Martín's answer:

Can you ping the DNS you want to use?

$ ping apple.com
ping: cannot resolve apple.com: Unknown host

What is/are the IP address(es) of the DNS(s) you want to use?

This is a company DNS server that is given with DHCP, it works well for other people. I've also tried Google's 8.8.4.4 and 205.171.3.65 (which I found from GRC's DNS Benchmark to be the fastest).

Have you tried using 8.8.8.8 (google) or any of the OpenDNS 208.67.222.222 or 208.67.220.220?

It doesn't work, see google chrome output:

The server at www.apple.com can't be found, because the DNS lookup failed. DNS is the network service that translates a website's name to its Internet address. This error is most often caused by having no connection to the Internet or a misconfigured network. It can also be caused by an unresponsive DNS server or a firewall preventing Google Chrome from accessing the network.

Can you ping those hosts?

$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8): 56 data bytes 64 bytes from
8.8.8.8: icmp_seq=0 ttl=58 time=3.925 ms

creating a blank user

A guest user account was created, the DNS issue was still there when using the guest account.

nslookup and dig both work fine

$ nslookup www.apple.com 8.8.8.8
Server:  8.8.8.8
Address: 8.8.8.8#53

Non-authoritative answer:
www.apple.com canonical name = www.isg-apple.com.akadns.net.
www.isg-apple.com.akadns.net canonical name = www.apple.com.edgekey.net.
www.apple.com.edgekey.net canonical name = e3191.c.akamaiedge.net.
Name: e3191.c.akamaiedge.net
Address: 184.24.141.15

 

$ dig @8.8.8.8 www.apple.com
; <<>> DiG 9.6.0-APPLE-P2 <<>> @8.8.8.8 www.apple.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 11298
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION: ;www.apple.com.   IN A
;; ANSWER SECTION:
www.apple.com.  1041 IN CNAME www.isg-apple.com.akadns.net.
www.isg-apple.com.akadns.net. 38 IN CNAME www.apple.com.edgekey.net.
www.apple.com.edgekey.net. 8794 IN CNAME e3191.c.akamaiedge.net.
e3191.c.akamaiedge.net. 17 IN A 184.24.141.15
;; Query time: 4 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Tue Oct 4 09:25:28 2011
;; MSG SIZE  rcvd: 158

also flushing the DNS cache was done but it didn't help

sudo dscacheutil -flushcache sudo killall -HUP mDNSResponder

EDIT 2:

$ cat /etc/resolv.conf
#
# Mac OS X Notice
#
# This file is not used by the host name and address resolution
# or the DNS query routing mechanisms used by most processes on
# this Mac OS X system.
#
# This file is automatically generated.
#
domain {redacted}.com
nameserver 8.8.8.8
nameserver 208.67.222.222
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Happens for me on lion as well. –  dkagedal Apr 28 '12 at 21:11
    
Happening for me on Mavericks, 10.9.4 –  greg7gkb Jul 2 at 20:15

10 Answers 10

up vote 37 down vote accepted

It turns out the solution was to bounce mDNSResponder:

sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

This was obtained by a different coworker from this Server Fault question.

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1  
Worked for me as well. Thanks! –  dkagedal Apr 28 '12 at 21:09
3  
But this isn't really a satisfactory answer. I need to know how to stop it from happening in the first place. –  dkagedal Aug 25 '12 at 23:57
    
My DNS (internet connection with IP addresses is fine, as is nslookup) also started going out, this brings it back without a reboot, thanks! –  Bogatyr Aug 27 '12 at 19:07
    
@dkagedal Will one of the other answers help? I'm really not familiar with networking, so this is not my forte. If you come up with a better prevention answer, please post it here! –  CajunLuke Sep 4 '12 at 19:42
1  
Got this problem on 10.9 and solution worked perfectly. In my case DNS was resolving for full names but not short ones. –  sorin Oct 29 '13 at 10:07

Actually, I think you might want to use

scutil --dns

scutil -r hostname

These commands use the dynamic store in configd, as opposed to the flatfiles in /etc, which often are only read in single user mode and for non networked systems.

man scutil   # or

scutil --help  
share|improve this answer
    
You don't explain why these commands would help with this problem. Do they even? Or this this meant as a comment to one of the other answers or something? –  dkagedal Sep 21 '12 at 19:58

I had the same exact same symptoms (and spend a while troubleshooting) but I was able to resolve it when I realized that I messed with /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist and what I did was somehow interpreted as malformed. I restored from a backup and the machine was able resolve hostnames again.

Before coming to the solution, I also realized that I was able to browse the internet if I used a socks5 proxy through "ssh -D" and tried DNS lookups through the tunnel.

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My company has been having this issue for months and months, each time taking Macs to the "Genius bar" whose only solution was to wipe the hard drives and start over. I saw your post, and deleted com.apple.mDNSResponder.plist, rebooted, and the problem was solved. I wish I could upvote you a billion times. –  Tom Thorogood Apr 3 '12 at 16:11
    
Do note delete com.apple.mDNSResponder.plist! I did it as @TomThorogood suggested. I have hard time to get back. Even I put the file back and restart I was unable to get any response from Internet. The sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist than helped. –  Pavel Mar 15 at 18:09

Name resolution under OSX (and UNIX in general) is taken from the IP addresses of the DNSs in the file located in /etc/resolv.conf (which OS X automatically generates as far as I can remember).

Since you've tried virtually anything that comes to my mind, I'd like to ask you:

  • Can you ping the DNS you want to use?
  • What is/are the IP address(es) of the DNS(s) you want to use?
  • Have you tried using 8.8.8.8 (google) or any of the OpenDNS 208.67.222.222 or 208.67.220.220?
  • Can you ping those hosts?

Finally, a usually nice test consists of creating a blank user and seeing if that new user exhibits the same problem. If it doesn't, then you can start digging what your current user has that could be causing the issue; if it also fails, then you know this is something more "system" related.

Also take a look around the Console to see if you can spot something that may be related (and would like to paste around here).

Last but not least, your Mac comes with two important DNS commands, nslookup and dig.

So to resolve www.apple.com using google's server, you'd type:

nslookup "host to resolve" "DNS server to use". E.g.:

$ nslookup www.apple.com 8.8.8.8
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
www.apple.com   canonical name = www.isg-apple.com.akadns.net.
www.isg-apple.com.akadns.net    canonical name = www.apple.com.edgekey.net.
www.apple.com.edgekey.net   canonical name = e3191.c.akamaiedge.net.
Name:   e3191.c.akamaiedge.net
Address: 184.24.141.15

NSLookup is an old command (that was supposed to be deprecated some years ago and replaced by DIG, but its easy to use syntax was too good to kill I guess.), its "replacement" is dig, a much more powerful command, whose syntax is more crazy.

To perform the same query, you'd type:

dig @8.8.8.8 www.apple.com

ANd here's the output:

$ dig @8.8.8.8 www.apple.com

; <<>> DiG 9.7.3 <<>> @8.8.8.8 www.apple.com
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17356
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.apple.com.         IN  A

;; ANSWER SECTION:
www.apple.com.      1782    IN  CNAME   www.isg-apple.com.akadns.net.
www.isg-apple.com.akadns.net. 42 IN CNAME   www.apple.com.edgekey.net.
www.apple.com.edgekey.net. 21581 IN CNAME   e3191.c.akamaiedge.net.
e3191.c.akamaiedge.net. 2   IN  A   184.24.141.15

;; Query time: 26 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Mon Oct  3 21:21:49 2011
;; MSG SIZE  rcvd: 158

As you can see, dig is much more "verbose" (which is good to debug what the heck is going on). The power of dig comes from the fact that you can specify what type of query you want to perform (Among other things).

In any case, let us know the exact outputs of these commands.

share|improve this answer
    
See my edit to the question. –  CajunLuke Oct 4 '11 at 19:33
    
@CajunLuke hmmmm interesting… I mind adding the output of: cat /etc/resolv.conf to your question? –  Martín Marconcini Oct 4 '11 at 22:10
    
Edited. (Padding to make comment fit.) –  CajunLuke Oct 4 '11 at 22:59
    
@CajunLuke i'm puzzled. Let's go back to the roots… this only happens on this machine, and only under OSX, the VMs are ok. I'm starting to suspect that Parallels or VMware may be causing some trouble. What type of network are these VMs using? Bridged? Shared? –  Martín Marconcini Oct 4 '11 at 23:22
    
It's VMware Fusion, and we're using the NAT option. There are probably twenty identical (imaged) machines, out of which two have this issue. OS X has the problem, VMs do not. –  CajunLuke Oct 4 '11 at 23:44

I've experienced the same problem… And while restarting mDNSResponder does seem to "work", restarting it a couple of times every hour sort of sucks.

So, for now, I've "solved" the problem by running dnsmasq locally. To do that:

  • Build dnsmasq (download the tgz and make or brew install dnsmasq)
  • Put this in a dnsmasq.conf file:
resolv-file=resolv.conf
user=nobody
group=nobody
interface=lo0
cache-size=1024
  • Put this in a resolv.conf file that is in the same directory as the dnsmasq.conf file (nb: not /etc/resolv.conf):
nameserver 8.8.8.8
nameserver 4.2.2.1
nameserver 4.2.2.2
  • Run dnsmasq with sudo dnsmasq --no-daemon --log-queries -C dnsmasq.conf. The output should look something like:
...
dnsmasq: reading resolv.conf
dnsmasq: using nameserver 4.2.2.1#53
dnsmasq: using nameserver 4.2.2.2#53
dnsmasq: using nameserver 8.8.8.8#53
dnsmasq: read /etc/hosts - 6 addresses
  • Open Network Preferences and make sure that 127.0.0.1 is the only DNS server (network preferences -> advanced -> DNS -> add 127.0.0.1)

Things should begin to work nicely again.

Once things are working, you can run dnsmasq without the --no-daemon and --log-queries options, so it will start in the background and you don't need to keep a Terminal window open.

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I had a very, very similar issue, except the symptoms were slightly different.

My user could not resolve any name (local NAS, Google etc) but a guest user on the same iMac (OS X 10.7.4) worked fine.

Flushing and restarting mDNSResponder as mentioned worked for a while. Whilst it would remain working when the iMac was put in sleep mode, it would always fail once rebooted.

When the flush/restart stopped working I looked for other reasons/solutions and I found that it was related to my firewall. I don't know what in my (OS X) firewall settings was causing it, but if I restored the firewall setting it worked.

To restore the default settings I used:

sudo cp /usr/libexec/ApplicationFirewall/com.apple.alf.plist /Library/Preferences/com.apple.alf.plist

Obviously any custom rules will have been removed with this restore.

I wanted to share my version of this issue as it's been causing me grief on and off for months and this post is the best collection of possible solutions on the net!

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I am having the same problem with 10.6.8. The first trip to an Apple Store resulted in system restore. But, after that, DNS broke again while I was overseas and didn't have a system DVD with me. At that time I found this thread and deleted /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist per @freezedpeanuts and @Tom Thorogood.

It fixed the problem, but, amazingly, DNS broke for the third time couple of days later. I hunted down a system image of 10.6.3 and:

  1. Copied /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist from the system image.
  2. sudo chown root /System/Library/LaunchDaemons/com.apple.mDNS*
  3. Rebooted

That fixed the problem.

It breaks periodically for me now (once a month or so), and the restore procedure is down to the steps above, except instead of rebooting you can:

sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.mDNSResponder.plist

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After upgrading from Snow Leopard on an old Mac Book to Mountain Lion, the system could not resolve DNS. Flushing, restart, nothing helped. Changing WiFi to a different Access point (my phone) helped.

Mountain Lion adds a new client field to the DHCP network settings. Filling in this field seemed to make the wifi access point happy. Leaving it blank meant nothing was getting thru, even though the wifi connection seemed to succeed.

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Turning Wi-Fi off and on again helped.

MacBook Pro with 10.9.1

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Please note to anyone still having issues, you might have to remove any public DNS servers until cache is cleared.

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