Note that iptos_ value must be decimal.

www/tutorial/advanced.html

@@ -372,7 +372,8 @@ example:
 
 <li> CBR: interval_ and rate_ are two way of specifying the same thing.
      iptos_ allows you to set the IP_TOS socket option for a traffic
-     stream.<pre>
+     stream.  Note that currently only decimal values are accepted for
+     the iptos_ value.<pre>
       $cbr0 start
       $cbr0 set packetSize_ 512
       $cbr0 set interval_ 0.01