I wrote a bash script that will find the current IP address of the WAN port on an Airport Extreme (and possibly other wireless routers) from the command line. It also works on a Linux-based computer, if you have the package net-smnp installed.
Go to the Advanced settings in your AirPort configuration, and select the Statistics tab. Make sure that 'Allow SNMP' is checked, and note the 'SNMP Community String -- it can be changed, but I would just keep it at public. Save your settings if they've been changed.
In the script below, the variable SNMPKEY needs to be changed if the 'SNMP Community String' is anything but public. You can also pass it from the command line if you wish. Here's the script:
if [ $# = 1 ] ; then
set -- $(netstat -nr | egrep '^0.0.0.0|^default')
set -- $(snmpwalk -Os -c "$SNMPKEY" -v 1 "$ROUTER" ipRouteNextHop.0.0.0.0)
set -- $(snmpwalk -Os -c "$SNMPKEY" -v 1 "$ROUTER" ipRouteNextHop.$4)
Back when 10.5 came out, this hint about enabling the screen sharing Bonjour browser was quite popular. Unfortunately, Apple disabled this very useful feature at some point during 10.5's life cycle, and it doesn't work in 10.6, either. In the course of my travels through the submission queue and Macworld's Mac Gems columns, I've come across a couple of possible replacements for this functionality.
First, there's Screen Sharing Launcher, an open source app that lets you add local computers to a list of available servers. When you want to screen share with another Mac, you just launch Screen Sharing Launcher instead, then select the desired machine.
This is a relatively new project, and it's not yet feature complete -- for instance, you can add machines to the list, but not remove them via the GUI. To remove them, you can edit the preferences file (with any pure text editor) directly; it's named net.curby.ScreenSharingLauncher.txt, and located in your user's Library » Preferences folder.
The other solution, and the one I've been personally using, is ScreenSharingMenulet, which is a faceless application that adds a new icon to the menu bar. Local hosts will show up automatically in the menu, or you can manually enter a host and add it to the My Computers section of the menu. Dan Frakes covered this app in an earlier Mac Gems column. The site's home page also lists two hidden preferences for controlling the display of IP addresses and the number of recent servers in the menu.
If you're aware of other replacements for the Bonjour browser, please list them in the comments...
After upgrading from Leopard to Snow Leopard, my MacBook would randomly stop resolving DNS names on my local network; most often occurring after awaking from sleep. The only way to "fix" this problem was to reboot. To add to the frustration of needing to reboot often, my Mac Mini continued to function without any of these troubles on the same network after being upgraded to Snow Leopard.
Symptoms included pings that would fail, I couldn't point my browser at web sites hosted on local servers, NFS mounts failing, and other general mayhem. Interestingly, while the MacBook was experiencing the problem, I'd run nslookup or dig on the DNS entry in question at a Terminal prompt, and it would return the correct information.
My network has a Fedora 11 box acting as a server with BIND DNS and DHCP running on it. Originally, I'd been publishing both my BIND and internet router as primary and secondary DNS servers respectively via DHCP. After removing the internet router as a secondary DNS, leaving only the BIND DNS, my MacBook magically began to work again.
I don't know the actual root cause and your milage may vary depending on your network setup.
Since Google announced their new free public DNS service, there has been a lot of talk about the speed of various DNS.
If you'd like to find the fastest DNS for your location, use the free Namebench, which tests well-known DNS as well as your regional DNS.
I had been using OpenDNS, but it turns out my ISP's DNS is 53% faster!
[robg adds: The test can take a while to run, and on my machine at least, I wasn't able to use the net while it was running -- lookups kept timing out until the test was over. The end result, though, is quite useful.]
In the past, people have submitted hints on how to get their Macs to start internet sharing automatically at boot. All of them are either editing files in hidden directories or creating a StartupItem to do the task. Most people may not want to edit files that are for the system, and Leopard and later versions of OS X use LaunchDaemons, not StartupItems to run scripts or executables at boot.
I created a LaunchDaemon plist based on the composition of the iStat Server's LaunchDaemon plist to run the InternetSharing executable automatically at boot. Here's what it looks like:
To install it, just copy the plist file into /Library/LaunchDaemons. The next time you reboot, the Internet Sharing option should already be turned on (once you're fully logged into a user account). The end result is identical to the older hints, but uses the new LaunchDaemon implementation rather than editing system files or installing a StartupItem.
After upgrading from 10.5.8 to 10.6.1 on my MacBook Pro, I was unable to connect to wireless networks unless I had already connected to them running under 10.5.8. Snow Leopard would "see" the new networks, but could not connect to them.
The Genius Bar at the Apple Store helped me solve the problem. We opened Library » Preferences » SystemConfiguration, and trashed the entire contents of that folder. We also deleted all locations in System Preferences » Network, and recreated the location Automatic. Finally, we rebooted.
So far, I have been able to connect to all wireless networks that I want to using OS X 10.6.1.
I have to manage several Macs in a lot of locations and I was very confortable with the Bonjour discovery, saved connections, and hidden features of the 10.5 Screen Sharing app. Alas, with the release of 10.6, they have gone -- Apple wants to sell Apple Remote Desktop.
I have found that using this command in Terminal...
defaults write com.apple.ScreenSharing controlObserveQuality n
...changes the quality of the connection's display, based on the value of n:
1 = black and white
2 = grayscale
3 = 8-bit color
4 = 16-bit color
5 = full color
I also set up shortcuts using the vnc://192.168.0.1 URL convention in Safari, as discussed in this hint and comments. I save all my connection shortcuts in a folder, and put that folder in my Dock. I now have a Saved Connections folder that I can use to launch Screen Sharing automatically.
[robg adds: This Terminal command was covered in this comment, but I felt it worth repeating as a full hint. If you have a Screen Sharing session currently open, you'll need to close and reopen it to see the changes.]