Several months ago I wrote up the v10 formatting for internal and external datagroups: iRules Data Group Formatting Rules. In v11, however, there is a change to the format of the internal data group ...
Ok - turns out the format is similar to the V10 rules. The following worked - note that if you give the CIDR you have to use "network" and not "host" even if it's a 32-bit netmask.