vnet/etc/scripts/icmp

packet-generator new {
  name x
  limit 1
  node ip4-input
  size 64-64
  no-recycle
  data {
    ICMP: 1.2.3.4 -> 5.6.7.8
    ICMP echo_request
    incrementing 100
  }
}

tr add pg-input 100
ip route 5.6.7.8/32 via local
ip route 1.2.3.4/32 via local