Strange DNS Performance and Observations...

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Level 1

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Strange DNS Performance and Observations...

I just got a new iMac last week. My wife can't stand it because the internet performance was very bad compared to our older Vista computer. (Actually I have 3 Vista machines, all work properly.)

With the help of other posts on this forum I have found a work around to the problem (assign the DNS servers to 4.2.2.2 and 4.2.2.1).

However, I thought I would share some of my personal observations regarding this problem:

1. Both Vista and iMac machines are plugged into the same 1 gig ethernet switch, which is connected to a Linksys router, which is connected to a cable modem.

2. The Vista machine doesn't have any problem using the DNS servers assigned from my router/ISP. Performance is always good.

3. The iMac internet performance using the default DNS servers is very spotty. Tonight was especially bad and some pages were returning an "web page not found" error. Traceroute was taking over 5s to lookup each route name.

4. Typically, I leave wireless disabled on the iMac. However, if I enable wireless on the iMac (using the my router/ISPs DNS servers) internet/dns performance is great. I verified this several times as I found this extremely strange...

5. I rebooted several times, and the problem did not go away.

Anyhow, from the amount of posts in the forum regarding this sort of issue, this definitely seems to be a problem (or incompatility) with OS X. Perhaps some of these observations can help Apple identify the issue.

-Sharkus

iMac 20" 2.0 Ghz, Mac OS X (10.5)

Posted on Nov 13, 2007 8:25 PM

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Answer 1

Dah•veed

Level 9

66,697 points

Nov 15, 2007 8:37 AM in response to Sharkus

I was experiencing rely slow responses to internet addresses back under Tiger, especially with websites I knew to be in the USA.. I discovered OpenDNS. I placed the two OpenDNS server addresses, 208.67.222.222 and 208.67.220.220, in System Prefs/Network as additions to the DNS server of my ISP. I gave them priority by placing them first in the Network settings. Everything is now very fast and responsive for me.
I have never opened an account with OpenDNS, but I understand a free account gives you more control over your internet access, such as parental controls with site blocking, etc.

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Answer 2

Dah•veed

Level 9

66,697 points

Nov 15, 2007 9:16 AM in response to Sharkus

Also, Linksys routers have a built in Dynamic DNS service which is disabled by default. Is this still disabled? If it is active could it be fighting what is configured into your Mac's network services?
Just a thought.

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Answer 3

sgoodis

Level 1

0 points

Dec 17, 2007 6:49 PM in response to Dah•veed

I was having the same issue. I have a 24" IMAC Intel based that I purchased in October. I have Verizon Fios and am use to operating at almost a T1 speed. All of the other computers in my house that were wireless were lightening fast - for for a few months my Apple crawled along at turtle speed. Funny thing - it only happened between the hours of 6PM to about midnight - in the morning it was always lightening fast.

I found this message board and gave the open DNS solution a try last night - and so far all day and all evening it has been faster than EVER.

The open DNS thing wasn't as easy to figure out as I thought - and I am still keeping both the wireless and bluetooth switched off - if that is what it takes then oh well - I'll suffer along with out those.

I pray that this is a permanent fix for me.

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Answer 4

capaho

Level 4

3,677 points

Dec 17, 2007 7:31 PM in response to Sharkus

OS X uses Bind to resolve domain names. When you enter name server information into the network settings, the name server info is written into the file /etc/resolv.conf like this:

nameserver 192.168.1.1

The above example is a LAN router IP address. In this case, the router uses PPPoE to connect to the ISP and gets its DNS via DHCP from the ISP. All the iMac has to do is query the router, which will then query the DNS servers specified by the ISP. I would expect this to be sufficient for most people who are using routers.

If you are connected directly to the Internet using a broadband modem, Bind should be getting the DNS information directly from the ISP.

Bind will query name servers in the order listed in resolv.conf. In the following example, Bind would query the OpenDNS name servers first and then the local router:

nameserver 208.67.222.222
nameserver 208.67.220.220
nameserver 192.168.1.1

I have a couple of G5 iMacs in addition to an aluminum iMac, and there is no difference between them as far as DNS queries go. I suspect the network slowdowns some people are experiencing have more to do with network configuration or settings, or ISP issues.

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