// common defns for IPv4 and IPv6
header ip46_t {
  bit<4> version;
  bit<4> reserved;
}

// header stack parsing
state parse_labels {
  packet.extract(hdr.labels.next);
  transition select(hdr.labels.last.bos) {
    0: parse_labels; // create loop
    1: guess_labels_payload;
  }
}

// lookahead parsing
state guess_labels_payload {
  transition select(packet.lookahead<ip46_t>().version) {
    4 : parse_inner_ipv4;
    6 : parse_inner_ipv6;
    default : parse_inner_ethernet;
  }
}