persistence at GTM

Ah, okay, I think I understand what you're asking now. You want any LDNS server within the CIDR block of the first LDNS request from that range to persist to the same target, yes? The persist command is not yet in the GTM feature set, so static persist with the CIDR notation is your best bet. You could layer your algorithms and choose an alternative method at the wideIP level by using multiple pools, then use static persist at the pool level, placing only one (or more if necessary) virtual server per pool so that after the pool selection is completed with your alternative algorithm at the wideIP level, the pool algorithm will ensure future request from that /16 are persisted appropriately.