Can i use time machine with a airport extreme and a external hard drive

Question

I have connected a hard drive to my airport extreme.
Now i would like to use time machine to back up my computers, and would like to do this on the hard drive which is connected to my airport extreme.
Next step is that i would like to be able to approach my external hard drive via the internet.
Is this possible or not?

Answer 1

Both are possible. However, Apple does NOT support Time Machine backups to AirPort Disks attached to the 802.11n AirPort Extreme Base Station (AEBSn). Doing so will potentially lead to data corruption and is highly not recommended. Please check out this excellent Pondini article for more details. This article also provides the Apple Support references that states Apple's position. Bottom line? If your backups are critical to you, then you may want to rethink your backup solution.
As far as accessing the AirPort Disk from the Internet, the following is the basic steps to do so:
Start the AirPort Utility > Select the AEBSn, and then, note the IP address shown.
Select Manual Setup.
Verify that Connection Sharing = Share a public IP address is selected on the Internet > Internet Connection tab.
Select Disks, and then, select File Sharing.
Verify that both the "Enable file sharing" and "Share disks over WAN" options are enabled.
Verify that Secure Shared Disks = With a disk password. (Recommended)
Verify that AirPort Disks Guest Access = Not allowed. (Recommended)
Select Advanced, and then, select the Port Mapping tab.
Click the plus sign to add a new port mapping.
For Service, select the "Personal File Sharing" option. (Note: This option would only allow Mac clients to access the AirPort Disks. If you want both Macs and PCs to connect, you would need to leave this field at its default value and enter the appropriate SMB ports to the mix of ports to be opened.)
In the Public UDP Port(s) and Public TCP Port(s) boxes, type in a 4-digit port number (e.g., 8888) that you choose. In the Private IP Address box, type the internal IP address of your AEBSn that you wrote down in step 1. In the Private UDP Port(s) and Private TCP Port(s) boxes, type 548. Click Continue.
In the Description box, type a descriptive name like "AirPort Disk File Sharing," and then, click Done.
Click on Update.
To connect to the shared AirPort Disk from a remote location using a Mac:
From the Finder > Go > Connect to Server.
Enter the Pubic (WAN-side) IP address of the AEBSn, followed by a colon and the Public port number that you choose in step 11 of the previous procedure. For example: afp://www.mydyndnsdomain.com:8888 or afp://123.456.789.123:8888
Click Connect.
You should be prompted for your user name and password. The user name can be anything you like; the password should be the Disk password for the AEBSn that you created in step 6 previously.
Click Connect.