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I'm running on 10.8.2. All of a sudden, traditional nameserver lookups are failing on my machine:

$ nslookup www.att.com
;; connection timed out; no servers could be reached

$ dig www.att.com

; <<>> DiG 9.8.3-P1 <<>> www.att.com
;; global options: +cmd
;; connection timed out; no servers could be reached

But operations that use name services work fine:

$ scutil -r www.att.com
Reachable


$ ping www.att.com
PING e2318.dscb.akamaiedge.net (23.1.57.145): 56 data bytes
64 bytes from 23.1.57.145: icmp_seq=0 ttl=55 time=22.862 ms
64 bytes from 23.1.57.145: icmp_seq=1 ttl=55 time=26.947 ms
^C
--- e2318.dscb.akamaiedge.net ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 22.862/24.904/26.947/2.043 ms

I've tried setting the name server addresses to different destinations via the network system preference (e.g., 4.2.2.2, 208.67.222.222, 208.67.220.220, etc.) but that doesn't seem to make any difference.

I'm guessing there is an internal configuration file for the on-board DNS server that isn't getting updated, but I haven't a clue where to look for that.

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What do you see if you run cat /etc/resolv.conf ? –  paulgrav Jan 2 '13 at 17:20
    
@paulgrav I the DNS settings from the network system preference reflected in /etc/resolv.conf. At the moment, it's pointing at my airport extreme:domain columbus.rr.com, nameserver 10.0.1.1 –  jhfrontz Jan 2 '13 at 21:04
    
What do you get if you run dig www.att.com @10.0.1.1 ? –  paulgrav Jan 3 '13 at 7:47
    
@paulgrav $ dig www.att.com *@*10.0.1.1 ; <<>> DiG 9.8.3-P1 <<>> www.att.com *@*10.0.1.1 ;; global options: +cmd ;; connection timed out; no servers could be reached –  jhfrontz Jan 3 '13 at 17:06
    
Sounds like your router is failing to resolve. Have you tried rebooting or reseting/updating? –  paulgrav Jan 3 '13 at 23:15
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3 Answers

I'm still not sure what was causing the problem, but after suffering from another seemingly unrelated issue, I did a complete re-install of 10.8. I had originally upgraded from 10.6 -- though the utilities had seemed to work fine for a while after the initial upgrade, my suspicion is that I did something to some unknown-to-me configuration while attempting to diagnose/resolve the other issue (something that apparently disabled some aspects of DNS access).

After the re-install, all DNS-related utilities are now working fine.

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nslookup does not use the system DNS settings to my knowledge, but rather queries the servers from resolv.conf directly.

ping, on the other hand, uses the system resolver to resolve names, and so the query might go to other DNS servers. For example, you can configure per-domain name servers in /etc/resolver, but these will not be used by nslookup. (see man 5 resolver)

Unfortunately, I don't know how to find out the IP of the DNS server that is finally used by the system resolver.

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I would dig into the results of:

 scutil --dns

And check that no firewall is blocking DNS packets (little snitch, IPFW, Apple's Application Firewall, etc…) and that port 53 is open between your Mac and the DNS servers listed from your scutil dumping of DNS options that are configured and in use.

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As far as I know, none of the usual suspects was to blame. –  jhfrontz Jul 22 '13 at 7:23
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