OSX Snow Leopard Not Finding Local DNS Names

April 2, 2010 by alex


We upgraded Sara's iMac to OSX 10.6. Mostly this is fine, but a few things are broken. Local DNS was one main problem. We have all our local machines in the '.dean' domain, and while I was able to correctly look up these names using dig, I wasn't able to actually use them in Firefox, ssh, or any other program.

The problem seems to be that 10.6 does not respect a DNS response with a TTL (time to live) of 0, which is the default value used by DNSMasq, the DNS/DHCP server which we use as part of DD-WRT.

The problem is described in this MacForums thread, in a posting by 'hphoto' dated '09-22-2009, 04:25 PM'.

The advice seems to be right-on. Raising the TTL to some non-0 value for local DNS seems to solve the problem. I chose 5 seconds for mine.

alex@schlitz:~$ dig grawp.dean

; <<>> DiG 9.4.3-P3 <<>> grawp.dean
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26685
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;grawp.dean.      IN  A

;; ANSWER SECTION:
grawp.dean.   0 IN  A 192.168.0.1

;; Query time: 13 msec
;; SERVER: 192.168.0.100#53(192.168.1.2)
;; WHEN: Fri Apr  2 21:46:05 2010
;; MSG SIZE  rcvd: 44

Notice the '0' in the ANSWER SECTION. That's the TTL.

Now go to the DD-WRT admin page for DNS options:

And add a 'local-ttl' value.

Then save your options.

These pages were useful for reference.

Notice that the options in the man page seem to be usable by just dropping the -- from the long version of the option. So --local-ttl=5 in the command- line version becomes just local-ttl=5 in the DD-WRT web interface.

Now, you can re-try that dig query to see the changed value.

alex@schlitz:~$ dig grawp.dean

; <<>> DiG 9.4.3-P3 <<>> grawp.dean
;; global options:  printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 26685
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;grawp.dean.      IN  A

;; ANSWER SECTION:
grawp.dean.   5 IN  A 192.168.0.1

;; Query time: 13 msec
;; SERVER: 192.168.0.100#53(192.168.1.2)
;; WHEN: Fri Apr  2 21:46:05 2010
;; MSG SIZE  rcvd: 44

Hope that helps!

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