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vereri · Jul 4, 2002, 01:32 AM

Well, the subject line pretty much says it. My cable ISP uses DHCP, and they are reluctant to reveal their DNS. I need it to set up a static IP on my OS X box on my subnet behind my Linksys router. Of course, I could go into the next room and run ipconfig/all on my Win2000 machine, but then I'd have to get up.

Plugging my router's address into Lookup in the Network Utility app, with Any/All Information selected did return the primary nameserver, but I'm nor sure what utility's for...I was just experimenting. I mean, that might have just been some error information being sent back. Plus, it didn't tell me the secondary DNS, and I want that too.

I browsed my various bin directories, trying commands that looked likely, but no dice.

Magicite · Jul 4, 2002, 02:48 AM

nslookup?

Mactoid · Jul 4, 2002, 02:48 AM

When you run the nslookup program it tells you the name and address of the default name server.

Camelot · Jul 4, 2002, 04:13 AM

<blockquote>quote:<hr />Originally posted by vereri:
Well, the subject line pretty much says it. My cable ISP uses DHCP, and they are reluctant to reveal their DNS. I need it to set up a static IP on my OS X box on my subnet behind my Linksys router. Of course, I could go into the next room and run ipconfig/all on my Win2000 machine, but then I'd have to get up.
<hr /></blockquote>Why do you care? You can use *ANY* DNS server - you do not have to use your ISPs DNS server.

For example, try "140.186.123.171" which is ns1.macnn.com

Detrius · Jul 5, 2002, 12:59 AM

<blockquote>quote:<hr />Originally posted by Camelot:
 <blockquote>quote:<hr />Originally posted by vereri:
Well, the subject line pretty much says it. My cable ISP uses DHCP, and they are reluctant to reveal their DNS. I need it to set up a static IP on my OS X box on my subnet behind my Linksys router. Of course, I could go into the next room and run ipconfig/all on my Win2000 machine, but then I'd have to get up.
<hr /></blockquote>Why do you care? You can use *ANY* DNS server - you do not have to use your ISPs DNS server.

For example, try "140.186.123.171" which is ns1.macnn.com<hr /></blockquote>Technically, if you use just ANY DNS server, then your internet connection will be slow and unreliable. For example, if you use the above DNS server, then every time you type in a web address, your computer has to send a request all the way out to the macnn server and then the response has to get all the way back before your computer can begin trying to go to the website. For websites with references to several different servers, this can add several seconds to the rendering of the page.

Amazing what minor details like that can change.

Oh, and if macnn ever goes down, so does your ability to surf the web easily.

Camelot · Jul 5, 2002, 03:49 PM

<blockquote>quote:<hr />Originally posted by Detrius:
Technically, if you use just ANY DNS server, then your internet connection will be slow and unreliable. For example, if you use the above DNS server, then every time you type in a web address, your computer has to send a request all the way out to the macnn server and then the response has to get all the way back before your computer can begin trying to go to the website. For websites with references to several different servers, this can add several seconds to the rendering of the page.

Amazing what minor details like that can change.

Oh, and if macnn ever goes down, so does your ability to surf the web easily.<hr /></blockquote>I disagree on the 'slow and unreliable' comment, Detrius.

First, there's no reason why it would be any less reliable. I picked macnn as an example just because it's clearly somewhere we all know. There's no reason why you couldn't pick 17.254.0.50 (nserver.apple.com) or 152.163.159.232 (dns-01.ns.aol.com) if you're concerned about the stability of MacNN's DNS servers (I assume you trust AOL and Apple

)

Secondly, there's a reason why you can specify multiple DNS servers in your TCP/IP configuration. Choosing two (or three) different DNS servers overcomes the potential problem of your primary DNS server being offline.

Thirdly, on the slow issue, yes, the FIRST lookup for any hostname will take a few milliseconds longer to lookup if the name server you choose is far away. However, this is mitigated by the fact that DNS responses are cached, so subsequent lookups take (essentially) no time at all, regardless of the DNS server you have setup.

Even if these few milliseconds are important to you, just find a large corporate name server that is close to you (for example, if you're in England, you might use 17.72.133.64 (nserver.euro.apple.com) rather than 17.254.0.50 (nserver.apple.com) - I'm sure you get the idea.)
I would certainly advocate this anyway, since using remote DNS servers can impact content delivery networks such as Akamai, which rely on DNS tricks to route you to a nearby server - if they think you're a user in San Jose because that's where your DNS request comes from but you're really in New York, you wont see as much benefit out of their network.

Finally, if you needed further convincing, what about all the people who use large national ISPs such as AOL, MSN or EarthLink. I don't use any of these, but I wouldn't be surprised to find all AOL users, for example, referring to a DNS server farm in Virginia rather than a local one. In this case, you would get BETTER DNS performance using my suggestion and manually using a local corporation's name server.

FWIW, you can find out exactly how long it takes to resolve DNS from various servers using dig. Try the following:

dig <a href="http://www.macnn.com" target="_blank">www.macnn.com</a> @nserver.apple.com
dig <a href="http://www.macnn.com" target="_blank">www.macnn.com</a> @dns-02.ns.aol.com
dig <a href="http://www.macnn.com" target="_blank">www.macnn.com</a> @ns1.earthlink.net
dig <a href="http://www.macnn.com" target="_blank">www.macnn.com</a> @ns1.macnn.com

and compare the times by looking for the 'Query time' listed near the bottom of the output. To be fair, run it a couple of times and average the results.

In my particular case, ns1.earthlink.net was the fastest, at 35ms, which is actually better than the 80ms returned by my ISP.

Note: you should check the DNS server before relying on it for everyday use. Some DNS servers are configured to not return replies for domains they are not responsible for (Microsoft's DNS servers, for example, won't respond to queries for non-Microsoft domains.

(fixed typo)

[ 07-05-2002, 03:54 PM: Message edited by: Camelot ]

Sword of Orion · Jul 5, 2002, 05:21 PM

ipfw will log DNS traffic, given the appropriate rules. I'm not on OS X right now, or I'd check to see if I have any rules that would log DNS. I know that in the past, I've seen three DNS servers listed in my log, one right after the other - so I assume that my Mac checked on all the ones that DHCP configured it for...

rantweasel · Jul 8, 2002, 02:49 AM

<blockquote>quote:<hr />Originally posted by Camelot:
Note: you should check the DNS server before relying on it for everyday use. Some DNS servers are configured to not return replies for domains they are not responsible for (Microsoft's DNS servers, for example, won't respond to queries for non-Microsoft domains.<hr /></blockquote>Also note:

<blockquote>code:<hr /><pre style="font-size:x-small; font-family: monospace;">mwegner@itachi ~>nslookup 4.2.2.4
Server: ns1.dca.net
Address: 204.183.80.2

Name: i-will-not-steal-service.gtei.net
Address: 4.2.2.4</pre><hr /></blockquote>Not every DNS server is for public consumption. Ask if it's okay, don't just assume that it's fair to take.

Gene Jockey · Jul 8, 2002, 10:03 PM

Assuming you're just leaving the DNS pane blank in the Network Pref Pane, the DNS servers fetched by DHCP will be listed in /etc/resolv.conf. So if you're looking for a command to see your name server, more /etc/resolv.conf would do the trick.

--J