Set a Maintenance page for specific IP subnet.

You can put the subnet in a data group and then call it in the irule with the page you want:

when CLIENT_ACCEPTED {
 
  Comparing a customer source IP to a list of entries in a LTM data-group.
 if { [class match [IP::remote_addr] equals data_SourceIps ] } {
   pool my_pool1
 } else {
   pool my_pool2
 }
 
}