Virtual Server - Block IP

In my opinion, the best way is to create an IP datagroup, then write an iRule like this:

 Datagroup which defines denied client IP addresses/networks
class denied_clients {
   network 10.0.0.0/8
   host 192.168.10.0/24
}

when CLIENT_ACCEPTED {
   if { [class match [IP::client_addr] equals denied_clients] }{
      log local0.  "client IP: [IP::client_addr] - discarded"
      discard
   }
}

To use a datagroup makes it easy to manage, whenever you want to add an IP subnet or delete an IP subnet, you can do it easily without touching to the iRule.