anchor.diff:  
   i_ip
   :
  -  IP i_ip_address
  +  IP
  +  (
  +    i_ip_address
  +    | i_ip_null
  +  )
   ;
   
   i_ip_address
   :
     ADDRESS addr = interface_address SECONDARY? (TAG tag = uint32)? NEWLINE
  +;
  +
  +i_ip_null
  +:
  +  REDIRECTS null_rest_of_line
   ;
   
   i_mtu
  
positive.code:   (
      i_no_autostate
      | i_no_bfd
      | i_no_shutdown
      | i_no_switchport
    )
  
negative.code:     | i_ip
      | i_mtu
      | i_no
      | i_shutdown
      | i_switchport
      | i_vrf_member
  