loop create
set int ip address loop0 192.168.1.1/8
set int state loop0 up

packet-generator new {
  name udp
  limit 512
  rate 1e4
  node ip4-input
  size 100-100
  interface loop0
  no-recycle
  data {
   UDP: 192.168.1.2 - 192.168.2.255 -> 192.168.1.1
   UDP: 4321 -> 1234
    length 72
    incrementing 100
  }
}