Check my DHCPD.conf config

What version of dhcpd are you using? I use v3.0.5-7 and I am experimenting with 4.0.0, if you are still having trouble you can email the conf offlist at jasonp <@> cablemo <.> com and I can take a stab at it for you.

In my subnets I use a pool decl to separate out the indivdual ranges, perhaps that is the problem. i.e. I would have written your cm pool like this

subnet 172.16.16.0 netmask 255.255.248.0 {
  pool {
    range 172.16.16.11 172.16.20.0;
    allow members of "CM";
    deny unknown-clients;
    option routers 172.16.16.10;
  }
}

Then put the other options in the CM class definition..

You could probably use option 82 and classes to do specific ips to cpe behind a specific modem i.e. something like this

class CMCustomer-023456
{
  spawn with option agent.remote-id;
  lease limit 1;
}

then inside your subnet create a pool and only allow members of that class

i.e.
subnet 10.0.0.0 netmask 255.255.255.0
{
  pool
  {
    range 10.0.0.2 10.0.0.2;
    allow members of "CMCustomer-023456";
  }
}

I think however that it would quickly get out of hand, and there would also be issues with leases not expiring. i.e. I have device A connected to modem decide to switch to device B when device B dhcps the only lease available is A's which has not expired and so it either gets another lease from main pool or is denied until Device A's lease is available. also only hosts and leases (and classes in newer versions of dhcpd) can be manipulated by omapi so you would have to make these changes in the dhcpd.conf itself.

here is some sample php5 code
<?php
error_reporting(E_ALL);
$clientIp = $_SERVER['REMOTE_ADDR'];
/*
Omapi/Omshell info
*/
$omapi_key = "your omapi key here";
$omapi_port = "9991";
$dhcpdServer = "your server ip";
$omshellPath = "/usr/bin/omshell";

function addOmapiModem($macAddress, $group)
{
 global $omapi_key;
 global $dhcpdServer;
 global $omapi_port;
 global $omshellPath;
 $dspec = array(0 => array("pipe", "r"), 1 => array("pipe", "w"), 2 => array("file", "/tmp/eo.txt", "a"),);
 $success = array();
 $success[0] = false;
 $success[1] = "";
 $process = proc_open($omshellPath, $dspec, $pipes);
 if (is_resource($process))
 {
  readit($pipes);
  writeit($pipes, "port $omapi_port");
  readit($pipes);
  writeit ($pipes, "key omapi_key \"$omapi_key\"");
  readit($pipes);
  writeit($pipes, "server $dhcpdServer");
  readit($pipes);
  writeit($pipes, "connect");
  $connected = readit($pipes);
  if ($connected == "obj: \n> ")
  {
   writeit($pipes, "new host");
   readit($pipes);
   writeit($pipes, "set known=1");
   readit($pipes);
   writeit($pipes, "set hardware-type=1");
   readit($pipes);
   $formatted_mac = ereg_replace(":$", "", chunk_split($macAddress, 2, ":"));
   writeit($pipes, "set hardware-address=$formatted_mac");
   readit($pipes);
   writeit($pipes, "set group=\"$group\"");
   readit($pipes);
   writeit($pipes, "create");
   $added = readit($pipes);
   if (ereg("^obj: host", $added) || ereg("open object: already exists", $added))
   {
    $success[0] = true;
   } else {
    $success[1] = $added;
   }
  }
  fclose($pipes[0]);
  fclose($pipes[1]);
  $return_value = proc_close($process);
 }
 return $success;
}

function readit($pipes, $end = '> ', $length = 1024)
{
 stream_set_blocking($pipes[1], FALSE);
 while (!feof($pipes[1]))
 {
  $buffer = fgets($pipes[1], $length);
  $returnValue .= $buffer;
  if (substr_count($buffer, $end) > 0) {
   $pipes[1] = "" ;
   break;
  }
 }
 return $returnValue;
}

function writeit ($pipes, $str)
{
   fwrite($pipes[0], "$str\n");
   return "$str\n";
}

?>

the way you ise it is like so

<?php
$result = addOmapiModem("001122334455", "Gold");
// if successful
if ($result[0] == true)
{
echo "successful";
} else {
// if not successful do something with error message
echo $result[1];
}
?>