Could you tell me the best way to upgrade cisco nac software from 4.1.3 to 4.7.2. What main issues i am likely to face when i do the upgrade?
You're right. 4.7.1 upgrade is through ISO and the .tar.gz option isn't available. For 4.7.2, if you use the ISO then you reimage it. To upgrade to 4.7.2, you have to use the .tar.gz.
Yes to number 1.
For going to 4.7.2 you'll have to use the .tar.gz file, NOT the ISO. If you use the ISO, you'll re-image your device. Also you have to run the .tar.gz upgrade script from the console and not in a SSH session!