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I have read the SuperUser blog post here about how Windows checks if there is an internet connection using NCSI. Is there an equivalent in the Mac world?

EDIT: I just found the post below at gossamer threads Posted by lorenzo at google Nov 15, 2012, 4:08 AM

"The Apple algorithm has drawbacks too. To wit: 

1. It biases in favour of IPv4 by trying the A record first. 
2. By always preferring the fastest protocol, even on a perfect dual-stack 
network it will use IPv6 only ~50% of the time (unless IPv4 is degraded). 
3. It imposes twice the connection load on server operators. 
4. It's non-deterministic, which some websites don't like as they tie your 
cookies to your IP address."  

I just haven't found any more details of the algorithm, eg what url / dns they use. My Google searches produce a lot of irrelevant information - can anyone point me in the right direction?

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Turn off wifi or remove the network cable, start wireshark and watch the traffic, then connect network again. You should see what sites are checked. –  ott-- Feb 12 '13 at 12:53
    
Good idea. I don't have the Mac, but I will suggest this if I can't get the data they are looking for. –  S List Feb 12 '13 at 12:56
    
Actually, second thoughts, this may not work. When I tried to ping www.msftncsi.com, I got this answer: "Ping wird ausgeführt für a1961.g.akamai.net [23.14.94.64] mit 32 Bytes Daten." In other words, I only got the local Akamai server. Akamai is the company that keeps NCSI up and running for Microsoft, I think. –  S List Feb 12 '13 at 13:37
    
What you mean local server? 23.14.94.64 is not in your local net. –  ott-- Feb 12 '13 at 14:42
    
I was just guessing, but would someone who accessed www.msftncsi.com from the other side of the world get the same server? And surely the guaranteed url is www.msftncsi.com, not whatever server Akamai chooses to put it on? –  S List Feb 12 '13 at 14:59

1 Answer 1

up vote 1 down vote accepted

Immediately upon starting my WiFi connection (really, at 0.077 seconds after) with no programs running on my 10.8.3 OSX Macbook Pro, the program applepushservicedm attempted a connection to 33-courier.push.apple.com on port 5223.

This IP address is affiliated with United States, and active in Cupertino, California and the program is part of the Apple Push Notification Service, therefore this may only apply to 10.8.

Seconds later, I made a DNS request to 1.courier-push-apple.com.akadns.net for iCloud.

This was all within the first 5 seconds, minus the standard DHCP, mDNS, NETBIOS, DNS registrations, NTP and miscellaneous crap that always occurs.

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Thanks for the info! –  S List Mar 28 '13 at 8:29
1  
Here is additional info. Apparently, the mDNS queries aren't innocuous after all! lists.apple.com/archives/ipv6-dev/2011/Jul/msg00009.html –  jnovack Mar 28 '13 at 19:31

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