Airport Utility

The company I work for decided to send me to a wireless networking class this week.  I like to think I know a fair amount about wireless networking, but I wanted to learn more so as to get the most functionality out of our Wireless Control System (WCS), Wireless LAN Controllers (WLC) and lightweight access points we have deployed across the enterprise.  After the first day, the instructor got me thinking about my own wireless setup at home.  The burning question I had was whether or not my Macs were utilizing 802.11n.  I have 3 Airport Extremes, two of which are “N” capable.  The third runs a separate SSID not used by any of my Macs.  When I finally got home and had a chance to poke around  their configuration a bit…well, lets just say I was surprised to find out that every wireless device (including my “N” capable Macs) were running at 802.11g even though they were associated to the “N” APs!

The next question I had was how to get them to connect at 802.11n rates.  Well, if you open Airport Utility, you’ll find under the “Wireless” tab the ability to modify the “Radio Mode.”  If you hold down the “Alt/Option” key and click the drop down, you’ll be presented with options you may never have seen before (At least I didn’t).  Now, I have the ability to select 802.11n only (5 GHz) which my Macs will support.  The only draw back is that my iPhone 4 only does 802.11n in the 2.4 GHz frequency spectrum.  That’s unfortunate because the 2.4 GHz spectrum is heavily used (i.e. wireless phones and microwaves).  However, there is another useful feature that Airport Utility gives us to play with.  If you click the “Advanced” icon at the top, then Logs and Statistics, you’ll see that you can check logs and view information about currently associated wireless clients.  The “Wireless Clients” tab includes Signal and Noise information about clients currently associated to that AP.  If you have a good signal to noise ratio (SNR) feel free to run in the 2.4 GHz spectrum (until someone wants popcorn).  To calculate SNR for a wireless AP, subtract Signal from Noise.  My values were -71 dBm and -96 dBm, respectively.  This gave me a SNR of 25dB which is good enough for wireless VoIP.  So, I decided to stay in the 2.4 GHz range.

There is, however, one last thing I think I should mention.  The two “N” capable APs I have are different hardware revisions.  The newest of the two has dual radios and the other does not.  The way to tell if your AP has two radios is whether or not you have the ability to setup a “Guest” network.  The reason I bring this up is that you may run into different options from the “Radio Mode” drop down menu depending on which hardware you own.  Enjoy!

-Tim

Exposé

While playing with my new iMac this weekend I happened on a feature of Mac OS X Snow Leopard that, surprisingly, I hadn’t come across before.  For the record, I’m not new to Snow Leopard (OS X 10.6) and one of the feature I quickly fell in love with in Leopard (10.5) was the introduction of Exposé.  The release of Snow Leopard brought a bit more sophistication to Exposé.  The obvious improvement I noticed was the more intuitive organization of windows upon activation.  To my surprise, Apple went a little bit further and I’ve only just come to realize it.  Exposé will now show the thumbnails of the windows that you have minimized to the Dock.  For all I know, this could have been introduced in 10.5 but it is still awesome regardless.

For those of you who are scratching your head, refer to the screenshot.  If you look closely at the image, you will see what looks like a recessed line towards the top of the image.  The line is the separator for the “maximized” windows (above the line) and the “minimized” windows (below the line).  In the example screenshot, the two thumbnails you see are two applications I had minimized (Screen Sharing and Safari).  As shown, if you move your mouse over one of the thumbnails, Exposé will give you a description of the thumbnail.  Pretty cool, huh?  Now if I can only break my long habit of Cmd+Tab to quickly switch between applications…

-Tim

Mac OS X Snow Leopard

Some of you may remember 10.6.3 breaking iChat on Mac OS X Snow Leopard Server.  Well,  it appears that the recent update to 10.6.4 from Apple yields the same results.  If you find yourself in the same boat as last time, fear not.  A simple fix is available:

sudo rm /private/var/jabberd/sqlite/jabberd2.db

Be sure to stop the iChat service in Server Admin first before you issue the above command.  Once issued, restart the service and you’ll be chatting again in no time.

-Tim

Cisco iPhone App

Every now and again, I like to run a search for “cisco” through Apple’s App Store.  My recent search came across this little beauty of an App.  Cisco has a couple other apps for iPhone on the App Store but this one will get the most use from me even though I have WebEX installed.  The Cisco App provides news, events, product updates, security advisories and more.  The app will also give you the ability to watch some of the product videos typically found at cisco.com.  So, grab yourself a copy if you are interested.

-Tim

I was the first one awake one weekend morning and saw it as a perfect time to have a nice cup of coffee and review some server logs and ensure everything is still working in proper order.  Every now and again, I’ll send test emails from my MobileMe email account to my domain account at timabbott.com.  After making some slight changes, I noticed that my email was not getting through.  A bit worried, I then sent an email from another account and was relieved to find that the message was delivered to my domain account immediately.  The question then became:  Why is my OS X Mail server not accepting mail from Apple?

Recipient address rejected: Service is unavailable;

A quick google of the above message lead me to this post on Apple’s discussion boards.  For those to lazy to click through, the thread discusses the greylisting feature in OS X 6.3 server as a means to combat spam.  While observing Mails behavior, I noticed that the messages I sent from MobileMe weren’t rejected, but simply delayed.  What’s more is that they weren’t stored locally on the server.  To provide that Mail’s spam filtering was the culprit, I temporarily turned off spam filtering.  At that point all email I sent from my MobileMe account was delivered immediately.  Re-enabling the feature caused my email to be delay by exactly one hour, which is was I now believe is the retry timer on Apple’s SMTP servers.  Now, I don’t have a problem with this feature but I do have a concern.  What if an email I want to receive is marked as spam by Mail and the sender’s server doesn’t try to deliver the message again?  Lost mail is my guess.  Luckily the nice folks at the Apple boards had a fix for that as well:

sudo pico /etc/postfix/main.cf

from

smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reje ct_unauth_destination check_policy_service unix:private/policy permit

to

smtpd_recipient_restrictions = permit_sasl_authenticated permit_mynetworks reje ct_unauth_destination permit

So if you are running into the same issue then you basically have three options:

1. Disable spam filtering (bad idea).
2. Disable greylisting
3. Do nothing

Personally, option three has my vote.  I can live with the delay and if I’m informed by an organization that mail to my domain is getting bounced I’ll tell them that it is an anti-spam mechanism and that there server should retry.

-Tim