text: from state import backend_ip_emap
  BACKEND_EXP_TIME = 3600000000 * 1000
  EXT_PORT = 2
  
  if a_packet_received:
      backend_ip_emap.expire_all(now - BACKEND_EXP_TIME)
  
  h3 = pop_header(tcpudp, on_mismatch=([],[]))
  h2 = pop_header(ipv4, on_mismatch=([],[]))
  h1 = pop_header(ether, on_mismatch=([],[]))
  
  bknd_addr = ip_addrc(h2.saddr)
  if received_on_port != EXT_PORT and backend_ip_emap.has(bknd_addr):
      backend_ip_emap.refresh_idx(backend_ip_emap.get(bknd_addr), now)
  else:
      pass
  