IP Range syntax question

I've got an iRule to send traffic from our office to a specific pool:

when CLIENT_ACCEPTED {
  if { [IP::addr [IP::client_addr] equals 123.100.45.100/123.100.45.188] } {
    pool employees-only-https
  }
}

Note: all staff use an address in the range 123.100.45.100 to 123.100.45.188

This seemed to work fine until this morning. Nothing seems to have changed. If I change the range to a single IP it works for those staff at that IP address.

Any ideas?