multiple default route base on physical interfaces

Hi,

I am following this link (http://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/tmos-ip-routing-administration-11-3-0/2.html) to create route domain & as per this I suppose to see Partition Default Route Domain list option while creating route domain route but it didn't.

They mentioned that (This setting does not appear if the current administrative partition is partition Common). What it does mean ? what do I need to do to get this option.

From the Partition Default Route Domain list, select either Another route domain (0) is the Partition Default Route Domain or Make this route domain the Partition Default Route Domain. This setting does not appear if the current administrative partition is partition Common. When you configure this setting, either route domain 0 or this route domain becomes the default route domain for the current administrative partition.