A few days ago I was touting one big benefit of OS X was that you could be on multiple IP subnets simultaneously.  Today I’m writing to let you know that this still works, but beware of the dumb mac users who try this…

Today I was trying to VPN into one of my clients networks.  The PPTP VPN connection would connect, but no traffic was sent.  I glanced in the Console in OS X and found this:

3/19/09 3/19/09, 9:58:07 PM pppd[1555] route_interface: write routing socket failed, File exists

After googling “route_interface: write routing socket failed, File exists” a bit, it dawned on me, that the second Ethernet interface I added the other day, was on the same subnet as my clients remote network.  So the PPTP VPN wouldn’t pass any traffic.  Once I disabled (or I could have changed IP addresses) the second Ethernet interface, the PPTP VPN started working perfectly again!

Occasionally I run into the error message that a volume can’t be ejected because it is in use.  Even though I don’t actively have anything being used on the share.  Today I got fed up with the error and decided to find a solution.

• Application:  lsof – list open files
• Usage:  lsof | grep sharename
• Example lsof | grep files

This will return a list of open files on that share.  You can then close the application that is holding the file open by either using the “Activity Monitor” or issuing a kill -9 PID.

Credit:  http://www.macosxhints.com/article.php?story=20080615071312194

I am constantly configuring firewalls and wireless access points for clients.  It has always been a pain to have to go offline for a while, while I switch the computer to use a different IP address while I’m configuring the device.  Today I was put in the same situation, except this time I’m using a Mac, and have a solution!

Its very simple, this is how its done:

• Go to System Preferences, Network
• Click the + symbol at the bottom of the device list to create a new interface
• On the interface selection, choose ethernet
• In the Service Name section, enter whatever you want to call the second interface, in my case Ethernet 2

Thats it!  Your done.  You can now configure the new interface to use whatever IP address you want and configure your device without leaving your native network.  Of course, this can also be done using your wireless interface as well.