iRule to manipulate designation content based off ip/subnet

If your IP matching is going to grow, you could build a class to clean up the rule. Also, since I assume that this is all HTTP traffic, you could move all the logic to the HTTP_REQUEST event to avoid setting the variable (or use info exists in the CLIENT_ACCEPTED event).

class my_exceptions {
  "156.74.138.63 GWWEB-HTTP"
  "156.74.12.223 GWWEB-HTTP"
  "156.74.12.222 GWWEB-HTTP"
  "10.10.10.10   DIFFERENT_POOL-HTTP"
}
when HTTP_REQUEST {
  if { [matchclass  [IP::client_addr] equals $::my_exceptions ]   } {
    log local0. "matched address [IP::client_addr] "
    pool [findclass [IP::client_addr] $::my_exceptions " " ]
  } elseif { not ( [IP::addr [IP::client_addr] equals 156.74.12.223 ] ) } {
      log local0. "matched subnet 156.74.16.0/24, issuing redirect..."
      HTTP::redirect "http://inweb.ci.seattle.wa.us/ccss/noaccess.asp"
  } else {
      log local0. "didn't match any addresses"
      pool GWWEB-HTTP
  }       
}

Note also that if you define GWWEB-HTTP as your default pool, you don't need the else statement...

Also note that the class is not part of the rule, it needs to be added under the datagroups tab in the GUI, or simply paste into to the bigip.conf file at the CLI and do a bigpipe load.

HTH

BTW, this compiled without error in the iRule Editor, but is untested.