anchor.diff:  
   
           # vm
  -        vm = CTRexScRaw( [ STLVmFlowVar(name="fv_rand",                            <1>
  +        vm = STLScVmRaw( [ STLVmFlowVar(name="fv_rand",                            <1>
                                           min_value=64, 
                                           max_value=len(base_pkt), 
                                           size=2, 
  
positive.code: 
          base_pkt  = Ether()/IP(dst="48.0.0.1")/TCP(dport=80,flags="S")
  
          vm = CTRexScRaw( [ STLVmFlowVar(name="ip_src",                              <1>
                                          min_value="16.0.0.0", 
                                          max_value="18.0.0.254", 
                                          size=4, op="inc"),
  
negative.code:                   IP(proto=17, chksum=5882, len=9202, ihl=5L, id=0) / 
                    UDP(dport=12, sport=1025, len=9182, chksum=55174) / 
                    Raw(load='!' * 9174))
          vm = STLScVmRaw([CTRexVmDescFlowVar(name='pkt_len', size=2, op='dec', 
                           init_value=9216, min_value=64, 
                           max_value=9216, step=1),
                           CTRexVmDescTrimPktSize(fv_name='pkt_len'),
  