iRule to redirect URL based on source address

You need a data-group existing that contains a list of allowed IPs or subnets for this iRule to work.

when HTTP_REQUEST {
  if { [string tolower [HTTP::path]] starts_with "/admin" and !([class match [IP::client_addr] equals data-group_of_IPs_and/or_subnets ]) } {
    HTTP::redirect "https://[HTTP::host]/"
    }
}