path: root/epan/dissectors/packet-bpdu.c

/* packet-bpdu.c
 * Routines for BPDU (Spanning Tree Protocol) disassembly
 *
 * Copyright 1999 Christophe Tronche <ch.tronche@computer.org>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * SPDX-License-Identifier: GPL-2.0-or-later
 */

#include "config.h"

#include <epan/packet.h>
#include <epan/llcsaps.h>
#include <epan/chdlctypes.h>
#include <epan/etypes.h>
#include <epan/addr_resolv.h>
#include <epan/prefs.h>
#include <epan/expert.h>
#include <epan/cisco_pid.h>

/* Offsets of fields within a BPDU */

#define BPDU_IDENTIFIER                           0
#define BPDU_VERSION_IDENTIFIER                   2
#define BPDU_TYPE                                 3
#define BPDU_FLAGS                                4
#define BPDU_ROOT_IDENTIFIER                      5
#define BPDU_ROOT_PATH_COST                      13
#define BPDU_BRIDGE_IDENTIFIER                   17
#define BPDU_PORT_IDENTIFIER                     25
#define BPDU_MESSAGE_AGE                         27
#define BPDU_MAX_AGE                             29
#define BPDU_HELLO_TIME                          31
#define BPDU_FORWARD_DELAY                       33
#define BPDU_VERSION_1_LENGTH                    35
#define BPDU_VERSION_3_LENGTH                    36
#define BPDU_MST_CONFIG_FORMAT_SELECTOR          38
#define BPDU_MST_CONFIG_NAME                     39
#define BPDU_MST_CONFIG_REVISION_LEVEL           71
#define BPDU_MST_CONFIG_DIGEST                   73
#define BPDU_CIST_INTERNAL_ROOT_PATH_COST        89
#define BPDU_CIST_BRIDGE_IDENTIFIER              93
#define BPDU_CIST_REMAINING_HOPS                101
#define BPDU_MSTI                               102

#define BPDU_PVST_TLV                            36

#define MSTI_FLAGS                                0
#define MSTI_REGIONAL_ROOT                        1
#define MSTI_INTERNAL_ROOT_PATH_COST              9
#define MSTI_BRIDGE_IDENTIFIER_PRIORITY          13
#define MSTI_PORT_IDENTIFIER_PRIORITY            14
#define MSTI_REMAINING_HOPS                      15


#define CONF_BPDU_SIZE                  35
#define TC_BPDU_SIZE                     4
#define MST_BPDU_SIZE                   38
#define VERSION_3_STATIC_LENGTH         64
#define MSTI_MESSAGE_SIZE               16

/* Values for the Alternative MSTI format */

#define ALT_BPDU_CIST_BRIDGE_IDENTIFIER         89
#define ALT_BPDU_CIST_INTERNAL_ROOT_PATH_COST   97

#define ALT_MSTI_MSTID                           0
#define ALT_MSTI_FLAGS                           2
#define ALT_MSTI_REGIONAL_ROOT                   3
#define ALT_MSTI_INTERNAL_ROOT_PATH_COST        11
#define ALT_MSTI_BRIDGE_IDENTIFIER              15
#define ALT_MSTI_PORT_IDENTIFIER                23
#define ALT_MSTI_REMAINING_HOPS                 25

#define ALT_MSTI_MESSAGE_SIZE                   26

/* Flag bits */

#define BPDU_FLAGS_TCACK                0x80
#define BPDU_FLAGS_AGREEMENT            0x40
#define BPDU_FLAGS_FORWARDING           0x20
#define BPDU_FLAGS_LEARNING             0x10
#define BPDU_FLAGS_PORT_ROLE_MASK       0x0C
#define BPDU_FLAGS_PORT_ROLE_SHIFT      2
#define BPDU_FLAGS_PROPOSAL             0x02
#define BPDU_FLAGS_TC                   0x01

void proto_register_bpdu(void);
void proto_reg_handoff_bpdu(void);

static int proto_bpdu = -1;
static int hf_bpdu_proto_id = -1;
static int hf_bpdu_version_id = -1;
static int hf_bpdu_type = -1;
static int hf_bpdu_flags = -1;
static int hf_bpdu_flags_tcack = -1;
static int hf_bpdu_flags_agreement = -1;
static int hf_bpdu_flags_forwarding = -1;
static int hf_bpdu_flags_learning = -1;
static int hf_bpdu_flags_port_role = -1;
static int hf_bpdu_flags_proposal = -1;
static int hf_bpdu_flags_tc = -1;
static int hf_bpdu_root_prio = -1;
static int hf_bpdu_root_sys_id_ext = -1;
static int hf_bpdu_root_mac = -1;
static int hf_bpdu_root_cost = -1;
static int hf_bpdu_bridge_prio = -1;
static int hf_bpdu_bridge_sys_id_ext = -1;
static int hf_bpdu_bridge_mac = -1;
static int hf_bpdu_port_id = -1;
static int hf_bpdu_msg_age = -1;
static int hf_bpdu_max_age = -1;
static int hf_bpdu_hello_time = -1;
static int hf_bpdu_forward_delay = -1;
static int hf_bpdu_version_1_length = -1;
static int hf_bpdu_version_3_length = -1;
static int hf_bpdu_mst_config_format_selector = -1;
static int hf_bpdu_mst_config_name = -1;
static int hf_bpdu_mst_config_revision_level = -1;
static int hf_bpdu_mst_config_digest = -1;
static int hf_bpdu_cist_internal_root_path_cost = -1;
static int hf_bpdu_cist_bridge_prio = -1;
static int hf_bpdu_cist_bridge_sys_id_ext = -1;
static int hf_bpdu_cist_bridge_mac = -1;
static int hf_bpdu_cist_remaining_hops = -1;
static int hf_bpdu_msti_flags = -1;
static int hf_bpdu_msti_id = -1;
static int hf_bpdu_msti_id_FFF = -1;
static int hf_bpdu_mst_priority = -1;
static int hf_bpdu_msti_regional_root_id = -1;
static int hf_bpdu_msti_regional_root_mac = -1;
static int hf_bpdu_msti_internal_root_path_cost = -1;
static int hf_bpdu_msti_bridge_identifier_priority = -1;
static int hf_bpdu_msti_port_identifier_priority = -1;
static int hf_bpdu_msti_port_id = -1;
static int hf_bpdu_msti_bridge_id = -1;
static int hf_bpdu_msti_bridge_id_priority = -1;
static int hf_bpdu_msti_bridge_id_mac = -1;
static int hf_bpdu_msti_remaining_hops = -1;
static int hf_bpdu_version_4_length = -1;
static int hf_bpdu_spt_config_format_selector = -1;
static int hf_bpdu_spt_config_name = -1;
static int hf_bpdu_spt_config_revision_level = -1;
static int hf_bpdu_spt_config_digest = -1;
static int hf_bpdu_flags_agree_num = -1;
static int hf_bpdu_flags_dagree_num = -1;
static int hf_bpdu_flags_agree_valid = -1;
static int hf_bpdu_flags_restricted_role = -1;
static int hf_bpdu_spt_agreement_digest = -1;
static int hf_bpdu_agreement_digest_format_id = -1;
static int hf_bpdu_agreement_digest_format_capabilities = -1;
static int hf_bpdu_agreement_digest_convention_id = -1;
static int hf_bpdu_agreement_digest_convention_capabilities = -1;
static int hf_bpdu_agreement_digest_edge_count = -1;

static int hf_bpdu_pvst_tlvtype = -1;
static int hf_bpdu_pvst_tlvlength = -1;
static int hf_bpdu_pvst_tlvvalue = -1;
static int hf_bpdu_pvst_tlv_origvlan = -1;

static gint ett_bpdu = -1;
static gint ett_bpdu_flags = -1;
static gint ett_root_id = -1;
static gint ett_bridge_id = -1;
static gint ett_mstp = -1;
static gint ett_msti = -1;
static gint ett_cist_bridge_id = -1;
static gint ett_spt = -1;
static gint ett_aux_mcid = -1;
static gint ett_agreement = -1;
static gint ett_bpdu_pvst_tlv = -1;

static expert_field ei_pvst_tlv_length_invalid = EI_INIT;
static expert_field ei_pvst_tlv_origvlan_missing = EI_INIT;
static expert_field ei_pvst_tlv_truncated = EI_INIT;
static expert_field ei_pvst_tlv_unknown = EI_INIT;
static expert_field ei_bpdu_type = EI_INIT;
static expert_field ei_bpdu_version_support = EI_INIT;


static gboolean bpdu_use_system_id_extensions = TRUE;

static dissector_handle_t gvrp_handle;
static dissector_handle_t gmrp_handle;

static dissector_handle_t bpdu_handle = NULL;
static dissector_handle_t bpdu_cisco_handle = NULL;

static const value_string protocol_id_vals[] = {
  { 0, "Spanning Tree Protocol" },
  { 0, NULL }
};

#define BPDU_PVST_TLV_ORIGVLAN  0               /* Originating VLAN TLV in Cisco (R)PVST+ BPDUs */

static const value_string bpdu_pvst_tlv_vals[] = {
  { BPDU_PVST_TLV_ORIGVLAN,             "Originating VLAN" },
  { 0,                                  NULL }
};


#define BPDU_TYPE_CONF                  0x00    /* STP Configuration BPDU */
#define BPDU_TYPE_RST                   0x02    /* RST BPDU (or MST) */
#define BPDU_TYPE_TOPOLOGY_CHANGE       0x80    /* STP TCN (Topology change notify) BPDU */

static const value_string bpdu_type_vals[] = {
  { BPDU_TYPE_CONF,            "Configuration" },
  { BPDU_TYPE_RST,             "Rapid/Multiple Spanning Tree" },
  { BPDU_TYPE_TOPOLOGY_CHANGE, "Topology Change Notification" },
  { 0,                         NULL }
};

#define PROTO_VERSION_STP       0
#define PROTO_VERSION_RSTP      2
#define PROTO_VERSION_MSTP      3
#define PROTO_VERSION_SPB       4

#define MSTI_FORMAT_UNKNOWN     0
#define MSTI_FORMAT_IEEE_8021S  1
#define MSTI_FORMAT_ALTERNATIVE 2

static const value_string version_id_vals[] = {
  { PROTO_VERSION_STP,  "Spanning Tree" },
  { PROTO_VERSION_RSTP, "Rapid Spanning Tree" },
  { PROTO_VERSION_MSTP, "Multiple Spanning Tree" },
  { PROTO_VERSION_SPB,  "Shortest Path Tree" },
  { 0,                  NULL}
};
static const value_string role_vals[] = {
  { 1, "Alternate or Backup" },
  { 2, "Root" },
  { 3, "Designated" },
  { 0, NULL }
};

static const char initial_sep[] = " (";
static const char cont_sep[] = ", ";

static void
dissect_bpdu_pvst_tlv(packet_info *pinfo, proto_tree *tree, tvbuff_t *tvb) {
  gboolean pvst_tlv_origvlan_present = FALSE;
  guint16 tlv_type, tlv_length;
  int offset = BPDU_PVST_TLV;
  proto_item * ti = NULL;
  proto_item * tlv_length_item = NULL;
  proto_tree * tlv_tree = NULL;

  if (tvb_reported_length_remaining(tvb, offset) < 4) /* TLV Type and Length fields occupy 4 bytes in total */
    expert_add_info(pinfo, tree, &ei_pvst_tlv_truncated);

  while (tvb_reported_length_remaining(tvb, offset) >= 4) { /* TLV Type and Length fields occupy 4 bytes in total */
    tlv_type = tvb_get_ntohs(tvb, offset);
    tlv_length = tvb_get_ntohs(tvb, offset + 2);

    tlv_tree = proto_tree_add_subtree(tree, tvb, offset, 4 + tlv_length,
                        ett_bpdu_pvst_tlv, &ti,
                        val_to_str(tlv_type, bpdu_pvst_tlv_vals, "Unknown TLV type: 0x%04x"));

    proto_tree_add_item(tlv_tree, hf_bpdu_pvst_tlvtype, tvb, offset, 2, ENC_BIG_ENDIAN);
    tlv_length_item = proto_tree_add_item(tlv_tree, hf_bpdu_pvst_tlvlength,
                        tvb, offset + 2, 2, ENC_BIG_ENDIAN);

    if (tvb_reported_length_remaining(tvb, offset + 4) < tlv_length) {
      expert_add_info(pinfo, tlv_length_item, &ei_pvst_tlv_truncated);
      break;
    }

    offset += 4;

    switch (tlv_type) {
      case BPDU_PVST_TLV_ORIGVLAN:
        if (tlv_length == 2) { /* Originating VLAN ID must be 2 bytes long */
          proto_item_append_text(ti, " (PVID): %u", tvb_get_ntohs(tvb, offset));
          proto_tree_add_item(tlv_tree, hf_bpdu_pvst_tlv_origvlan, tvb, offset, tlv_length, ENC_BIG_ENDIAN);
          pvst_tlv_origvlan_present = TRUE;
        }
        else
          expert_add_info(pinfo, tlv_length_item, &ei_pvst_tlv_length_invalid);
        break;

      default:
        proto_tree_add_item(tlv_tree, hf_bpdu_pvst_tlvvalue, tvb, offset, tlv_length, ENC_NA);
        expert_add_info(pinfo, tlv_tree, &ei_pvst_tlv_unknown);
        break;
    }

    offset += tlv_length;
  }

  if (pvst_tlv_origvlan_present == FALSE) /* If a (R)PVST+ BPDU lacks the Originating VLAN TLV, it is malformed */
    expert_add_info(pinfo, tree, &ei_pvst_tlv_origvlan_missing);
}

static void
dissect_bpdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, gboolean is_bpdu_pvst)
{
  guint16 protocol_identifier;
  guint8  protocol_version_identifier;
  guint8  bpdu_type;
  guint8  flags;
  guint16 root_identifier_bridge_priority;
  guint16 root_identifier_system_id_extension = 0;
  const gchar *root_identifier_mac_str;
  guint32 root_path_cost;
  guint16 bridge_identifier_bridge_priority;
  guint16 bridge_identifier_system_id_extension = 0;
  const gchar *bridge_identifier_mac_str;
  guint16 port_identifier;
  double message_age;
  double max_age;
  double hello_time;
  double forward_delay;
  guint8 version_1_length;
  guint16 version_3_length;
  guint16 version_4_length = 0;
  guint16 bpdu_version_4_length = 0;
  guint8 config_format_selector;
  guint16 cist_bridge_identifier_bridge_priority;
  guint16 cist_bridge_identifier_system_id_extension = 0;
  const gchar *cist_bridge_identifier_mac_str;
  guint32 msti_regional_root_mstid, msti_regional_root_priority;
  const gchar *msti_regional_root_mac_str;
  guint16 msti_bridge_identifier_priority, msti_port_identifier_priority;
  int   total_msti_length, offset, msti, msti_format;
  int   msti_length_remaining;

  int spt_offset = 0;

  int MCID_LEN = 51;
  guint8 spt_agree_data = 0;

  proto_tree *bpdu_tree;
  proto_tree *mstp_tree, *msti_tree, *spt_tree = NULL, *aux_mcid_tree = NULL, *agreement_tree = NULL;
  proto_item *bpdu_item;
  proto_item *agreement_item, *proto_id_item, *type_item;
  proto_tree *root_id_tree;
  proto_tree *bridge_id_tree;
  proto_tree *cist_bridge_id_tree;
  const char *sep;

  static const int * bpdu_flags[] = {
    &hf_bpdu_flags_tcack,
    &hf_bpdu_flags_tc,
    NULL
  };

  static const int * rst_flags[] = {
    &hf_bpdu_flags_tcack,
    &hf_bpdu_flags_agreement,
    &hf_bpdu_flags_forwarding,
    &hf_bpdu_flags_learning,
    &hf_bpdu_flags_port_role,
    &hf_bpdu_flags_proposal,
    &hf_bpdu_flags_tc,
    NULL
  };

  /* GARP application frames require special interpretation of the
     destination address field; otherwise, they will be mistaken as
     BPDU frames.
     Fortunately, they can be recognized by checking the first 6 octets
     of the destination address, which are in the range from
     01-80-C2-00-00-20 to 01-80-C2-00-00-2F.

     Yes - we *do* need to check the destination address type;
     on Linux cooked captures, there *is* no destination address,
     so it's AT_NONE. */
  if (pinfo->dl_dst.type == AT_ETHER) {
    const guint8 *dstaddr;

    dstaddr = (const guint8 *)pinfo->dl_dst.data;
    if(dstaddr[0] == 0x01 && dstaddr[1] == 0x80 &&
       dstaddr[2] == 0xC2 && dstaddr[3] == 0x00 &&
       dstaddr[4] == 0x00 && ((dstaddr[5] == 0x0D) || ((dstaddr[5] & 0xF0) == 0x20))) {

      switch (dstaddr[5]) {

      case 0x20:
        /* for GMRP */
        call_dissector(gmrp_handle, tvb, pinfo, tree);
        return;

      case 0x21:
      case 0x0D:
        /* for GVRP */
        call_dissector(gvrp_handle, tvb, pinfo, tree);
        return;
      }
      col_set_str(pinfo->cinfo, COL_PROTOCOL, "GARP");
        /* Generic Attribute Registration Protocol */

      col_add_fstr(pinfo->cinfo, COL_INFO,
                   "Unknown GARP application (0x%02X)",
                   dstaddr[5]);

      return;
    }
  }

  col_set_str(pinfo->cinfo, COL_PROTOCOL, "STP"); /* Spanning Tree Protocol */
  col_clear(pinfo->cinfo, COL_INFO);

  bpdu_type = tvb_get_guint8(tvb, BPDU_TYPE);

  protocol_version_identifier = tvb_get_guint8(tvb, BPDU_VERSION_IDENTIFIER);

  switch (bpdu_type) {

  case BPDU_TYPE_CONF:
  case BPDU_TYPE_RST:
    flags = tvb_get_guint8(tvb, BPDU_FLAGS);
    root_identifier_bridge_priority = tvb_get_ntohs(tvb,BPDU_ROOT_IDENTIFIER);
    if (bpdu_use_system_id_extensions ) {
      root_identifier_system_id_extension = root_identifier_bridge_priority & 0x0fff;
      root_identifier_bridge_priority &= 0xf000;
    }
    root_identifier_mac_str = tvb_ether_to_str(tvb, BPDU_ROOT_IDENTIFIER + 2);
    root_path_cost = tvb_get_ntohl(tvb, BPDU_ROOT_PATH_COST);
    port_identifier = tvb_get_ntohs(tvb, BPDU_PORT_IDENTIFIER);
    break;

  default:
    /* Squelch GCC complaints. */
    flags = 0;
    root_identifier_bridge_priority = 0;
    root_identifier_mac_str = NULL;
    root_path_cost = 0;
    port_identifier = 0;
    break;
  }

  switch (bpdu_type) {

  case BPDU_TYPE_CONF:
    if (bpdu_use_system_id_extensions ) {
      col_add_fstr(pinfo->cinfo, COL_INFO,
                   "Conf. %sRoot = %d/%d/%s  Cost = %d  Port = 0x%04x",
                   flags & 0x1 ? "TC + " : "",
                   root_identifier_bridge_priority,
                   root_identifier_system_id_extension,
                   root_identifier_mac_str,
                   root_path_cost, port_identifier);
    } else {
      col_add_fstr(pinfo->cinfo, COL_INFO,
                   "Conf. %sRoot = %d/%s  Cost = %d  Port = 0x%04x",
                   flags & 0x1 ? "TC + " : "",
                   root_identifier_bridge_priority, root_identifier_mac_str,
                   root_path_cost, port_identifier);
    }
    break;

  case BPDU_TYPE_TOPOLOGY_CHANGE:
    col_set_str(pinfo->cinfo, COL_INFO, "Topology Change Notification");
    break;

  case BPDU_TYPE_RST:
    if (bpdu_use_system_id_extensions ) {
      col_add_fstr(pinfo->cinfo, COL_INFO,
                   "%sT. %sRoot = %d/%d/%s  Cost = %d  Port = 0x%04x",
                     protocol_version_identifier == 3 ? "MS":
                     (protocol_version_identifier == 4 ? "SP":"RS"),
                     flags & 0x1 ? "TC + " : "",
                     root_identifier_bridge_priority,
                     root_identifier_system_id_extension,
                     root_identifier_mac_str,
                     root_path_cost, port_identifier);
    } else {
      col_add_fstr(pinfo->cinfo, COL_INFO,
                   "%sT. %sRoot = %d/%s  Cost = %d  Port = 0x%04x",
                   protocol_version_identifier == 3 ? "MS":
                   (protocol_version_identifier == 4 ? "SP":"RS"),
                   flags & 0x1 ? "TC + " : "",
                   root_identifier_bridge_priority, root_identifier_mac_str,
                   root_path_cost, port_identifier);
    }
    break;

  default:
    col_add_fstr(pinfo->cinfo, COL_INFO, "Unknown BPDU type (%u)", bpdu_type);
    break;
  }

    bpdu_item = proto_tree_add_protocol_format(tree, proto_bpdu, tvb, 0, -1,
                                               "Spanning Tree Protocol");
    bpdu_tree = proto_item_add_subtree(bpdu_item, ett_bpdu);

    protocol_identifier = tvb_get_ntohs(tvb, BPDU_IDENTIFIER);
    proto_tree_add_uint(bpdu_tree, hf_bpdu_proto_id, tvb, BPDU_IDENTIFIER, 2,
                        protocol_identifier);

    proto_id_item = proto_tree_add_uint(bpdu_tree, hf_bpdu_version_id, tvb,
                        BPDU_VERSION_IDENTIFIER, 1,
                        protocol_version_identifier);
    switch (protocol_version_identifier) {

    case 0:
      break;

    case 2:
    case 3:
    case 4:
      break;

    default:
      expert_add_info(pinfo, proto_id_item, &ei_bpdu_version_support);
      break;
    }
    type_item = proto_tree_add_uint(bpdu_tree, hf_bpdu_type, tvb, BPDU_TYPE, 1, bpdu_type);

    if (bpdu_type == BPDU_TYPE_TOPOLOGY_CHANGE) {
      set_actual_length(tvb, TC_BPDU_SIZE);
      return;
    }

    if (bpdu_type != BPDU_TYPE_CONF && bpdu_type != BPDU_TYPE_RST) {
      /* Unknown BPDU type - just display the rest of the PDU as data */
      expert_add_info(pinfo, type_item, &ei_bpdu_type);
      return;
    }

    bridge_identifier_bridge_priority = tvb_get_ntohs(tvb, BPDU_BRIDGE_IDENTIFIER);
    if (bpdu_use_system_id_extensions ) {
      bridge_identifier_system_id_extension = bridge_identifier_bridge_priority & 0x0fff;
      bridge_identifier_bridge_priority &= 0xf000;
    }
    bridge_identifier_mac_str = tvb_ether_to_str(tvb, BPDU_BRIDGE_IDENTIFIER + 2);

    if (bpdu_type == BPDU_TYPE_RST) {
       proto_tree_add_bitmask_value_with_flags(bpdu_tree, tvb, BPDU_FLAGS, hf_bpdu_flags, ett_bpdu_flags, rst_flags, flags, BMT_NO_FALSE|BMT_NO_TFS);
    } else {
       proto_tree_add_bitmask_value_with_flags(bpdu_tree, tvb, BPDU_FLAGS, hf_bpdu_flags, ett_bpdu_flags, bpdu_flags, flags, BMT_NO_FALSE|BMT_NO_TFS);
    }

    /* add Identifier with format based on preference value
     * bpdu_use_system_id_extensions
     * */
    if (bpdu_use_system_id_extensions) {
      root_id_tree = proto_tree_add_subtree_format(bpdu_tree, tvb,
                                         BPDU_ROOT_IDENTIFIER, 8,
                                         ett_root_id, NULL,
                                         "Root Identifier: %d / %d / %s",
                                         root_identifier_bridge_priority,
                                         root_identifier_system_id_extension,
                                         root_identifier_mac_str);
      proto_tree_add_uint(root_id_tree, hf_bpdu_root_prio, tvb,
                          BPDU_ROOT_IDENTIFIER , 1,
                          root_identifier_bridge_priority);
      proto_tree_add_uint(root_id_tree, hf_bpdu_root_sys_id_ext, tvb,
                          BPDU_ROOT_IDENTIFIER , 2,
                          root_identifier_system_id_extension);
      proto_tree_add_item(root_id_tree, hf_bpdu_root_mac, tvb,
                          BPDU_ROOT_IDENTIFIER + 2, 6, ENC_NA);

    } else {
      root_id_tree = proto_tree_add_subtree_format(bpdu_tree, tvb,
                                         BPDU_ROOT_IDENTIFIER, 8,
                                         ett_root_id, NULL,
                                         "Root Identifier: %d / %s",
                                         root_identifier_bridge_priority,
                                         root_identifier_mac_str);
      proto_tree_add_uint(root_id_tree, hf_bpdu_root_prio, tvb,
                          BPDU_ROOT_IDENTIFIER , 2,
                          root_identifier_bridge_priority);
      proto_tree_add_item(root_id_tree, hf_bpdu_root_mac, tvb,
                          BPDU_ROOT_IDENTIFIER + 2, 6, ENC_NA);
    }
    /* end of Identifier formatting */

    proto_tree_add_uint(bpdu_tree, hf_bpdu_root_cost, tvb,
                        BPDU_ROOT_PATH_COST, 4, root_path_cost);

    /* add Identifier with format based on preference value
     * bpdu_use_system_id_extensions
     * */
    if (bpdu_use_system_id_extensions) {
      bridge_id_tree = proto_tree_add_subtree_format(bpdu_tree, tvb,
                                           BPDU_BRIDGE_IDENTIFIER, 8,
                                           ett_bridge_id, NULL,
                                           "Bridge Identifier: %d / %d / %s",
                                           bridge_identifier_bridge_priority,
                                           bridge_identifier_system_id_extension,
                                           bridge_identifier_mac_str);
      proto_tree_add_uint(bridge_id_tree, hf_bpdu_bridge_prio, tvb,
                          BPDU_BRIDGE_IDENTIFIER , 1,
                          bridge_identifier_bridge_priority);
      proto_tree_add_uint(bridge_id_tree, hf_bpdu_bridge_sys_id_ext, tvb,
                          BPDU_BRIDGE_IDENTIFIER , 2,
                          bridge_identifier_system_id_extension);
      proto_tree_add_item(bridge_id_tree, hf_bpdu_bridge_mac, tvb,
                          BPDU_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);
    } else {
      bridge_id_tree = proto_tree_add_subtree_format(bpdu_tree, tvb,
                                           BPDU_BRIDGE_IDENTIFIER, 8,
                                           ett_bridge_id, NULL,
                                           "Bridge Identifier: %d / %s",
                                           bridge_identifier_bridge_priority,
                                           bridge_identifier_mac_str);
      proto_tree_add_uint(bridge_id_tree, hf_bpdu_bridge_prio, tvb,
                          BPDU_BRIDGE_IDENTIFIER , 2,
                          bridge_identifier_bridge_priority);
      proto_tree_add_item(bridge_id_tree, hf_bpdu_bridge_mac, tvb,
                          BPDU_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);
    }
    /* end of Identifier formatting */

    proto_tree_add_uint(bpdu_tree, hf_bpdu_port_id, tvb,
                        BPDU_PORT_IDENTIFIER, 2, port_identifier);
    message_age = tvb_get_ntohs(tvb, BPDU_MESSAGE_AGE) / 256.0;
    proto_tree_add_double(bpdu_tree, hf_bpdu_msg_age, tvb, BPDU_MESSAGE_AGE, 2,
                          message_age);
    max_age = tvb_get_ntohs(tvb, BPDU_MAX_AGE) / 256.0;
    proto_tree_add_double(bpdu_tree, hf_bpdu_max_age, tvb, BPDU_MAX_AGE, 2,
                          max_age);
    hello_time = tvb_get_ntohs(tvb, BPDU_HELLO_TIME) / 256.0;
    proto_tree_add_double(bpdu_tree, hf_bpdu_hello_time, tvb,
                          BPDU_HELLO_TIME, 2, hello_time);
    forward_delay = tvb_get_ntohs(tvb, BPDU_FORWARD_DELAY) / 256.0;
    proto_tree_add_double(bpdu_tree, hf_bpdu_forward_delay, tvb,
                          BPDU_FORWARD_DELAY, 2, forward_delay);

    if (bpdu_type == BPDU_TYPE_CONF) {
      if (is_bpdu_pvst)
        dissect_bpdu_pvst_tlv(pinfo, bpdu_tree, tvb);

      /* Nothing more in this BPDU */
      set_actual_length(tvb, CONF_BPDU_SIZE);
      return;
    }

    /* RST or MST BPDU */
    version_1_length = tvb_get_guint8(tvb, BPDU_VERSION_1_LENGTH);
    proto_tree_add_uint(bpdu_tree, hf_bpdu_version_1_length, tvb,
                        BPDU_VERSION_1_LENGTH, 1, version_1_length);
    /* Is this an MST BPDU? */
    if (protocol_version_identifier >= 3 && version_1_length == 0 &&
        tvb_reported_length(tvb) >= 102) {
      /*
       * OK, it passes the "Protocol Identifier is 0000 0000
       * 0000 0000", "Protocol Version Identifier is 3 or
       * greater", "BPDU Type is 0000 0010", "contains 102 or
       * more octets", and "a Version 1 Length of 0" tests.
       */
      version_3_length = tvb_get_ntohs(tvb, BPDU_VERSION_3_LENGTH);
      proto_tree_add_uint(bpdu_tree, hf_bpdu_version_3_length, tvb,
                          BPDU_VERSION_3_LENGTH, 2, version_3_length);

      /*
       * Check the Version 3 Length, and see whether it's a
       * multiple of the MSTI Configuration Message length. Also
       * check the config_format_selector because some MST BPDU's
       * have BPDU_VERSION_3_LENGTH set to 0 and use the
       * field BPDU_MST_CONFIG_FORMAT_SELECTOR as a length-field
       * for the MSTI data.
       */
      config_format_selector = tvb_get_guint8(tvb, BPDU_MST_CONFIG_FORMAT_SELECTOR);
      if (version_3_length != 0) {
        msti_format = MSTI_FORMAT_IEEE_8021S;
        if (version_3_length >= VERSION_3_STATIC_LENGTH) {
          total_msti_length = version_3_length - VERSION_3_STATIC_LENGTH;
        } else {
          /*
           * XXX - there appears to be an ambiguity in the 802.3Q-2003
           * standard and at least some of the 802.3s drafts.
           *
           * The "Version 3 Length" field is defined to be "the number of
           * octets taken by the parameters that follow in the BPDU", but
           * it's spoken of as "representing an integral number, from 0 to
           * 64 inclusive, of MSTI Configuration Messages".
           *
           * According to mail from a member of the stds-802-1@ieee.org list,
           * the latter of those is just saying that the length must not have
           * a value that implies that there's a partial MSTI message in the
           * packet; it's still in units of octets, not messages.
           *
           * However, it appears that Cisco's C3550 software (C3550-I5Q3L2-M,
           * Version 12.1(12c)EA1) might be sending out lengths in units of
           * messages.
           *
           * This length can't be the number of octets taken by the parameters
           * that follow in the BPDU, because it's less than the fixed-length
           * portion of those parameters, so we assume the length is a count of
           * messages.
           */
          total_msti_length = version_3_length * MSTI_MESSAGE_SIZE;
        }
      } else {
        if (tvb_reported_length(tvb) == (guint)config_format_selector + MST_BPDU_SIZE + 1 ) {
          msti_format = MSTI_FORMAT_ALTERNATIVE;
          total_msti_length = config_format_selector - VERSION_3_STATIC_LENGTH;
        } else {
          /*
           * XXX - Unknown MSTI format, since version_3_length is 0
           * lets assume there are no msti instances in the packet.
           */
          msti_format = MSTI_FORMAT_UNKNOWN;
          total_msti_length = 0;
        }
      }
      if (protocol_version_identifier == 3) {
        set_actual_length(tvb, BPDU_MSTI + total_msti_length);
      }

      mstp_tree = proto_tree_add_subtree(bpdu_tree, tvb, BPDU_VERSION_3_LENGTH,
                                      -1, ett_mstp, NULL, "MST Extension");

      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_format_selector, tvb,
                          BPDU_MST_CONFIG_FORMAT_SELECTOR, 1, ENC_BIG_ENDIAN);
      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_name, tvb,
                          BPDU_MST_CONFIG_NAME, 32, ENC_ASCII|ENC_NA);

      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_revision_level, tvb,
                          BPDU_MST_CONFIG_REVISION_LEVEL, 2, ENC_BIG_ENDIAN);
      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_digest, tvb,
                          BPDU_MST_CONFIG_DIGEST, 16, ENC_NA);

      switch(msti_format) {

      case MSTI_FORMAT_IEEE_8021S:
        proto_tree_add_item(mstp_tree, hf_bpdu_cist_internal_root_path_cost, tvb,
                            BPDU_CIST_INTERNAL_ROOT_PATH_COST, 4, ENC_BIG_ENDIAN);

        cist_bridge_identifier_bridge_priority = tvb_get_ntohs(tvb,BPDU_CIST_BRIDGE_IDENTIFIER);
        cist_bridge_identifier_mac_str = tvb_ether_to_str(tvb, BPDU_CIST_BRIDGE_IDENTIFIER + 2);

        /* add Identifier with format based on preference value
         * bpdu_use_system_id_extensions
         * */
        if (bpdu_use_system_id_extensions ) {
          cist_bridge_identifier_system_id_extension = cist_bridge_identifier_bridge_priority & 0x0fff;
          cist_bridge_identifier_bridge_priority &= 0xf000;

          cist_bridge_id_tree = proto_tree_add_subtree_format(mstp_tree, tvb,
                                                    BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                                                    ett_cist_bridge_id, NULL,
                                                    "CIST Bridge Identifier: %d / %d / %s",
                                                    cist_bridge_identifier_bridge_priority,
                                                    cist_bridge_identifier_system_id_extension,
                                                    cist_bridge_identifier_mac_str);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_prio, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER , 1,
                              cist_bridge_identifier_bridge_priority);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_sys_id_ext, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER , 2,
                              cist_bridge_identifier_system_id_extension);
          proto_tree_add_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);

        } else {
          cist_bridge_id_tree = proto_tree_add_subtree_format(mstp_tree, tvb,
                                                    BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                                                    ett_cist_bridge_id, NULL,
                                                    "CIST Bridge Identifier: %d / %s",
                                                    cist_bridge_identifier_bridge_priority,
                                                    cist_bridge_identifier_mac_str);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_prio, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER , 2,
                              cist_bridge_identifier_bridge_priority);
          proto_tree_add_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);
        }
        /* end of Identifier formatting */

        break;

      case MSTI_FORMAT_ALTERNATIVE:
        cist_bridge_identifier_bridge_priority = tvb_get_ntohs(tvb,ALT_BPDU_CIST_BRIDGE_IDENTIFIER);
        cist_bridge_identifier_mac_str = tvb_ether_to_str(tvb, ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2);

        /* add Identifier with format based on preference value
         * bpdu_use_system_id_extensions
         * */
        if (bpdu_use_system_id_extensions ) {
          cist_bridge_identifier_system_id_extension = cist_bridge_identifier_bridge_priority & 0x0fff;
          cist_bridge_identifier_bridge_priority &= 0xf000;

          cist_bridge_id_tree = proto_tree_add_subtree_format(mstp_tree, tvb,
                                                    ALT_BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                                                    ett_cist_bridge_id, NULL,
                                                    "CIST Bridge Identifier: %d / %d / %s",
                                                    cist_bridge_identifier_bridge_priority,
                                                    cist_bridge_identifier_system_id_extension,
                                                    cist_bridge_identifier_mac_str);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_prio, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER , 1,
                              cist_bridge_identifier_bridge_priority);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_sys_id_ext, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER , 2,
                              cist_bridge_identifier_system_id_extension);
          proto_tree_add_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);
        } else {
          cist_bridge_id_tree = proto_tree_add_subtree_format(mstp_tree, tvb,
                                                    ALT_BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                                                    ett_cist_bridge_id, NULL,
                                                    "CIST Bridge Identifier: %d / %s",
                                                    cist_bridge_identifier_bridge_priority,
                                                    cist_bridge_identifier_mac_str);
          proto_tree_add_uint(cist_bridge_id_tree, hf_bpdu_cist_bridge_prio, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER , 2,
                              cist_bridge_identifier_bridge_priority);
          proto_tree_add_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);
        }
        /* end of Identifier formatting */

        proto_tree_add_item(mstp_tree, hf_bpdu_cist_internal_root_path_cost, tvb,
                            ALT_BPDU_CIST_INTERNAL_ROOT_PATH_COST, 4, ENC_BIG_ENDIAN);

        break;
      }

      proto_tree_add_item(mstp_tree, hf_bpdu_cist_remaining_hops, tvb,
                          BPDU_CIST_REMAINING_HOPS, 1, ENC_BIG_ENDIAN);
      /* MSTI messages */
      offset = BPDU_MSTI;
      msti = 1;
      msti_length_remaining = total_msti_length;
      while (msti_length_remaining > 0) {
        switch(msti_format) {

        case MSTI_FORMAT_IEEE_8021S:
          msti_regional_root_mstid = tvb_get_guint8(tvb,  offset+ MSTI_REGIONAL_ROOT);
          msti_regional_root_priority = (msti_regional_root_mstid &0xf0) << 8;
          msti_regional_root_mstid = ((msti_regional_root_mstid & 0x0f) << 8) +
                                     tvb_get_guint8(tvb,  offset+ MSTI_REGIONAL_ROOT+1);
          msti_regional_root_mac_str = tvb_ether_to_str(tvb, offset + MSTI_REGIONAL_ROOT + 2);

          msti_tree = proto_tree_add_subtree_format(mstp_tree, tvb, offset, 16, ett_msti, NULL,
                                          "MSTID %d, Regional Root Identifier %d / %s",
                                          msti_regional_root_mstid,
                                          msti_regional_root_priority,
                                          msti_regional_root_mac_str);

          /* flags */
          proto_tree_add_bitmask_with_flags(msti_tree, tvb, offset+MSTI_FLAGS, hf_bpdu_msti_flags, ett_bpdu_flags, rst_flags, ENC_NA, BMT_NO_FALSE|BMT_NO_TFS);

          /* pri, MSTID, Regional root */
          proto_tree_add_item(msti_tree, hf_bpdu_mst_priority, tvb, offset + MSTI_REGIONAL_ROOT, 1, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_id_FFF, tvb, offset + MSTI_REGIONAL_ROOT, 2, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                                            offset + MSTI_REGIONAL_ROOT + 2, 6, ENC_NA);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_internal_root_path_cost, tvb,
                              offset+MSTI_INTERNAL_ROOT_PATH_COST, 4, ENC_BIG_ENDIAN);

          msti_bridge_identifier_priority = tvb_get_guint8(tvb, offset+MSTI_BRIDGE_IDENTIFIER_PRIORITY) >> 4;
          msti_port_identifier_priority = tvb_get_guint8(tvb, offset+MSTI_PORT_IDENTIFIER_PRIORITY) >> 4;

          proto_tree_add_uint(msti_tree, hf_bpdu_msti_bridge_identifier_priority, tvb,
                              offset+MSTI_BRIDGE_IDENTIFIER_PRIORITY, 1,
                              msti_bridge_identifier_priority);
          proto_tree_add_uint(msti_tree, hf_bpdu_msti_port_identifier_priority, tvb,
                              offset+MSTI_PORT_IDENTIFIER_PRIORITY, 1,
                              msti_port_identifier_priority);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_remaining_hops, tvb,
                              offset + MSTI_REMAINING_HOPS, 1, ENC_BIG_ENDIAN);

          msti_length_remaining -= MSTI_MESSAGE_SIZE;
          offset += MSTI_MESSAGE_SIZE;
          break;

        case MSTI_FORMAT_ALTERNATIVE:
          msti_regional_root_mstid = tvb_get_guint8(tvb,  offset+ ALT_MSTI_REGIONAL_ROOT);
          msti_regional_root_priority = (msti_regional_root_mstid &0xf0) << 8;
          msti_regional_root_mstid = ((msti_regional_root_mstid & 0x0f) << 8) +
                                     tvb_get_guint8(tvb,  offset+ ALT_MSTI_REGIONAL_ROOT+1);
          msti_regional_root_mac_str = tvb_ether_to_str(tvb, offset+ ALT_MSTI_REGIONAL_ROOT + 2);

          msti_tree = proto_tree_add_subtree_format(mstp_tree, tvb, offset, 16, ett_msti, NULL,
                                          "MSTID %d, Regional Root Identifier %d / %s",
                                          msti_regional_root_mstid,
                                          msti_regional_root_priority,
                                          msti_regional_root_mac_str);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_id, tvb, offset+ALT_MSTI_MSTID, 2, ENC_BIG_ENDIAN);

          /* flags */
          proto_tree_add_bitmask_with_flags(msti_tree, tvb, offset+ALT_MSTI_FLAGS, hf_bpdu_msti_flags, ett_bpdu_flags, rst_flags, ENC_NA, BMT_NO_FALSE|BMT_NO_TFS);

          /* pri, MSTID, Regional root */
          proto_tree_add_item(msti_tree, hf_bpdu_mst_priority, tvb, offset + ALT_MSTI_REGIONAL_ROOT, 1, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_regional_root_id, tvb, offset + ALT_MSTI_REGIONAL_ROOT, 2, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                                            offset + ALT_MSTI_REGIONAL_ROOT + 2, 6, ENC_NA);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_internal_root_path_cost, tvb,
                              offset+ALT_MSTI_INTERNAL_ROOT_PATH_COST, 4, ENC_BIG_ENDIAN);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_bridge_id, tvb, offset + ALT_MSTI_BRIDGE_IDENTIFIER, 2, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_bridge_id_priority, tvb, offset + ALT_MSTI_BRIDGE_IDENTIFIER, 2, ENC_BIG_ENDIAN);
          proto_tree_add_item(msti_tree, hf_bpdu_msti_bridge_id_mac, tvb,
                                            offset + ALT_MSTI_BRIDGE_IDENTIFIER + 2, 6, ENC_NA);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_port_id, tvb, offset+ALT_MSTI_PORT_IDENTIFIER, 2, ENC_BIG_ENDIAN);

          proto_tree_add_item(msti_tree, hf_bpdu_msti_remaining_hops, tvb,
                              offset + ALT_MSTI_REMAINING_HOPS, 1, ENC_BIG_ENDIAN);

          msti_length_remaining -= ALT_MSTI_MESSAGE_SIZE;
          offset += ALT_MSTI_MESSAGE_SIZE;
          break;
        }
        msti++;
      }

      if (protocol_version_identifier >= 4 && version_1_length == 0
          && tvb_reported_length(tvb) >= 106) {
        /*
         * OK, it passes the "Protocol Identifier is 0000 0000
         * 0000 0000", "Protocol Version Identifier is 4 or
         * greater", "BPDU Type is 0000 0010", "contains 106 or
         * more octets", and "a Version 1 Length of 0" tests.
         */
        bpdu_version_4_length = BPDU_MSTI + total_msti_length;
        version_4_length = tvb_get_ntohs(tvb, bpdu_version_4_length);

        proto_tree_add_uint(bpdu_tree, hf_bpdu_version_4_length, tvb,
                            bpdu_version_4_length, 2, version_4_length);

        /* version 4 length is 55 or more.
         */
        if (version_4_length >= 53) {
          static const int * agreements[] = {
              &hf_bpdu_flags_agree_num,
              &hf_bpdu_flags_dagree_num,
              &hf_bpdu_flags_agree_valid,
              &hf_bpdu_flags_restricted_role,
              NULL
          };

          spt_tree = proto_tree_add_subtree(bpdu_tree, tvb, bpdu_version_4_length, -1,
              ett_spt, NULL, "SPT Extension");

          spt_offset = (bpdu_version_4_length + 2);

          /* Aux MCID: */

          aux_mcid_tree = proto_tree_add_subtree(spt_tree, tvb, spt_offset,
                                              MCID_LEN, ett_aux_mcid, NULL, "MCID Data");

          proto_tree_add_item(aux_mcid_tree,
                              hf_bpdu_spt_config_format_selector, tvb, spt_offset, 1,
                              ENC_BIG_ENDIAN);
          proto_tree_add_item(aux_mcid_tree, hf_bpdu_spt_config_name, tvb,
                              spt_offset + 1, 32, ENC_ASCII | ENC_NA);

          proto_tree_add_item(aux_mcid_tree,
                              hf_bpdu_spt_config_revision_level, tvb, spt_offset + 33,
                              2, ENC_BIG_ENDIAN);
          proto_tree_add_item(aux_mcid_tree, hf_bpdu_spt_config_digest,
                              tvb, spt_offset + 35, 16, ENC_NA);
          spt_offset += MCID_LEN;

          /* Agreement Data */
          agreement_tree = proto_tree_add_subtree(spt_tree, tvb, spt_offset,
                                               -1, ett_agreement, &agreement_item, "Agreement Data");

          spt_agree_data = tvb_get_guint8(tvb, spt_offset);

          sep = initial_sep;
          proto_item_append_text(agreement_item, "%sAN: %d", sep, (spt_agree_data & 0x03));

          proto_tree_add_bitmask_list_value(agreement_tree, tvb, spt_offset, 1, agreements, spt_agree_data);
          sep = cont_sep;

          proto_item_append_text(agreement_item, "%sDAN: %d", sep, ((spt_agree_data & 0x0C) >> 2));

          if (sep != initial_sep) {
            proto_item_append_text(agreement_item, ")");
          }
          spt_offset += 2;

          proto_tree_add_item(agreement_tree, hf_bpdu_agreement_digest_format_id, tvb, spt_offset, 1, ENC_NA);
          proto_tree_add_item(agreement_tree, hf_bpdu_agreement_digest_format_capabilities, tvb, spt_offset, 1, ENC_NA);
          spt_offset += 1;

          proto_tree_add_item(agreement_tree, hf_bpdu_agreement_digest_convention_id, tvb, spt_offset, 1, ENC_NA);
          proto_tree_add_item(agreement_tree, hf_bpdu_agreement_digest_convention_capabilities, tvb, spt_offset, 1, ENC_NA);
          spt_offset += 1;

          proto_tree_add_item(agreement_tree, hf_bpdu_agreement_digest_edge_count, tvb, spt_offset, 2, ENC_BIG_ENDIAN);
          spt_offset += 10;

          proto_tree_add_item(agreement_tree, hf_bpdu_spt_agreement_digest,
                              tvb, spt_offset, 20, ENC_NA);
          /*spt_offset += 20;*/

          if (protocol_version_identifier == 4) {
            set_actual_length(tvb, (bpdu_version_4_length + version_4_length + 2));
          }
        }
      }
    } else { /* It is RSTP BPDU and may still be Rapid PVST+ */
      if (is_bpdu_pvst)
        dissect_bpdu_pvst_tlv(pinfo, bpdu_tree, tvb);
    }
}

static int
dissect_bpdu_cisco(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
  dissect_bpdu(tvb, pinfo, tree, TRUE);
  return tvb_captured_length(tvb);
}

static int
dissect_bpdu_generic(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree, void* data _U_)
{
  dissect_bpdu(tvb, pinfo, tree, FALSE);
  return tvb_captured_length(tvb);
}

void
proto_register_bpdu(void)
{

  static hf_register_info hf[] = {
    { &hf_bpdu_proto_id,
      { "Protocol Identifier",          "stp.protocol",
        FT_UINT16,      BASE_HEX,       VALS(protocol_id_vals), 0x0,
        NULL, HFILL }},
    { &hf_bpdu_version_id,
      { "Protocol Version Identifier",  "stp.version",
        FT_UINT8,       BASE_DEC,       VALS(version_id_vals),  0x0,
        NULL, HFILL }},
    { &hf_bpdu_type,
      { "BPDU Type",                    "stp.type",
        FT_UINT8,       BASE_HEX,       VALS(bpdu_type_vals),   0x0,
        NULL, HFILL }},
    { &hf_bpdu_flags,
      { "BPDU flags",                   "stp.flags",
        FT_UINT8,       BASE_HEX,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_flags_tcack,
      { "Topology Change Acknowledgment",  "stp.flags.tcack",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_TCACK,
        NULL, HFILL }},
    { &hf_bpdu_flags_agreement,
      { "Agreement",                    "stp.flags.agreement",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_AGREEMENT,
        NULL, HFILL }},
    { &hf_bpdu_flags_forwarding,
      { "Forwarding",                   "stp.flags.forwarding",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_FORWARDING,
        NULL, HFILL }},
    { &hf_bpdu_flags_learning,
      { "Learning",                     "stp.flags.learning",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_LEARNING,
        NULL, HFILL }},
    { &hf_bpdu_flags_port_role,
      { "Port Role",                    "stp.flags.port_role",
        FT_UINT8,       BASE_DEC,       VALS(role_vals),        BPDU_FLAGS_PORT_ROLE_MASK,
        NULL, HFILL }},
    { &hf_bpdu_flags_proposal,
      { "Proposal",                     "stp.flags.proposal",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_PROPOSAL,
        NULL, HFILL }},
    { &hf_bpdu_flags_tc,
      { "Topology Change",              "stp.flags.tc",
        FT_BOOLEAN,     8,              TFS(&tfs_yes_no),       BPDU_FLAGS_TC,
        NULL, HFILL }},
    { &hf_bpdu_root_prio,
      { "Root Bridge Priority",         "stp.root.prio",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_root_sys_id_ext,
      { "Root Bridge System ID Extension",      "stp.root.ext",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_root_mac,
      { "Root Bridge System ID",        "stp.root.hw",
        FT_ETHER,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_root_cost,
      { "Root Path Cost",               "stp.root.cost",
        FT_UINT32,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_bridge_prio,
      { "Bridge Priority",              "stp.bridge.prio",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_bridge_sys_id_ext,
      { "Bridge System ID Extension",   "stp.bridge.ext",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_bridge_mac,
      { "Bridge System ID",             "stp.bridge.hw",
        FT_ETHER,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_port_id,
      { "Port identifier",              "stp.port",
        FT_UINT16,      BASE_HEX,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msg_age,
      { "Message Age",                  "stp.msg_age",
        FT_DOUBLE,      BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_max_age,
      { "Max Age",                      "stp.max_age",
        FT_DOUBLE,      BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_hello_time,
      { "Hello Time",                   "stp.hello",
        FT_DOUBLE,      BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_forward_delay,
      { "Forward Delay",                "stp.forward",
        FT_DOUBLE,      BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_version_1_length,
      { "Version 1 Length",             "stp.version_1_length",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_pvst_tlvtype,
      { "Type",                         "stp.pvst.tlvtype",
        FT_UINT16,      BASE_HEX,       VALS(bpdu_pvst_tlv_vals),       0x0,
        NULL, HFILL }},
    { &hf_bpdu_pvst_tlvlength,
      { "Length",                       "stp.pvst.tlvlen",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_pvst_tlv_origvlan,
      { "Originating VLAN",             "stp.pvst.origvlan",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_pvst_tlvvalue,
      { "Value",        "stp.pvst.tlvval",
        FT_BYTES,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_version_3_length,
      { "Version 3 Length",             "mstp.version_3_length",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_mst_config_format_selector,
      { "MST Config ID format selector",        "mstp.config_format_selector",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_mst_config_name,
      { "MST Config name",              "mstp.config_name",
        FT_STRINGZ,     BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_mst_config_revision_level,
      { "MST Config revision",          "mstp.config_revision_level",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_mst_config_digest,
      { "MST Config digest",            "mstp.config_digest",
        FT_BYTES,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_cist_internal_root_path_cost,
      { "CIST Internal Root Path Cost",         "mstp.cist_internal_root_path_cost",
        FT_UINT32,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_cist_bridge_prio,
      { "CIST Bridge Priority",         "mstp.cist_bridge.prio",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_cist_bridge_sys_id_ext,
      { "CIST Bridge Identifier System ID Extension",   "mstp.cist_bridge.ext",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_cist_bridge_mac,
      { "CIST Bridge Identifier System ID",     "mstp.cist_bridge.hw",
        FT_ETHER,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_cist_remaining_hops,
      { "CIST Remaining hops",          "mstp.cist_remaining_hops",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_flags,
      { "MSTI flags",                   "mstp.msti.flags",
        FT_UINT8,       BASE_HEX,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_mst_priority,
      { "Priority",                   "mstp.msti.priority",
        FT_UINT8,       BASE_HEX,       NULL,   0xF0,
        NULL, HFILL }},
    { &hf_bpdu_msti_id_FFF,
      { "MSTID",                   "mstp.msti.msti_id",
        FT_UINT16,       BASE_DEC,       NULL,   0x0FFF,
        NULL, HFILL }},
    { &hf_bpdu_msti_id,
      { "MSTID",                   "mstp.msti.msti_id",
        FT_UINT16,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_regional_root_id,
      { "MSTI Regional Root Identifier", "mstp.msti.regional_root_id",
        FT_UINT16,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_regional_root_mac,
      { "Regional Root",                "mstp.msti.root.hw",
        FT_ETHER,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_internal_root_path_cost,
      { "Internal root path cost",              "mstp.msti.root_cost",
        FT_UINT32,      BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_bridge_id,
      { "MSTI Bridge Identifier",          "mstp.msti.bridge_id",
        FT_UINT16,       BASE_DEC,       NULL,   0x0FFF,
        NULL, HFILL }},
    { &hf_bpdu_msti_bridge_id_priority,
      { "MSTI Bridge Priority",            "mstp.msti.bridge_id_priority",
        FT_UINT16,       BASE_DEC,       NULL,   0xF000,
        NULL, HFILL }},
    { &hf_bpdu_msti_bridge_id_mac,
      { "MSTI Bridge MAC",                "mstp.msti.bridge_id_mac",
        FT_ETHER,       BASE_NONE,      NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_bridge_identifier_priority,
      { "Bridge Identifier Priority",           "mstp.msti.bridge_priority",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_port_identifier_priority,
      { "Port identifier priority",             "mstp.msti.port_priority",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_port_id,
      { "Port identifier",              "mstp.msti.port",
        FT_UINT16,      BASE_HEX,       NULL,   0x0,
        NULL, HFILL }},
    { &hf_bpdu_msti_remaining_hops,
      { "Remaining hops",               "mstp.msti.remaining_hops",
        FT_UINT8,       BASE_DEC,       NULL,   0x0,
        NULL, HFILL }},
        { &hf_bpdu_version_4_length,
           { "Version 4 Length",                "mstp.version_4_length",
        FT_UINT16,      BASE_DEC,       NULL,   0x0,
                NULL, HFILL }},
    { &hf_bpdu_spt_config_format_selector,
          { "SPT Config ID format selector",    "mstp.config_format_selector",
        FT_UINT8, BASE_DEC, NULL, 0x0,
                NULL, HFILL }},
        { &hf_bpdu_spt_config_name,
          {"SPT Config name",   "mstp.config_name",
        FT_STRINGZ, BASE_NONE, NULL, 0x0,
            NULL, HFILL } },
        { &hf_bpdu_spt_config_revision_level,
          { "SPT Config revision",    "mstp.config_revision_level",
        FT_UINT16, BASE_DEC, NULL, 0x0,
            NULL, HFILL } },
        { &hf_bpdu_spt_config_digest,
          { "SPT Config digest",    "mstp.config_digest",
        FT_BYTES, BASE_NONE, NULL, 0x0,
            NULL, HFILL } },
        { &hf_bpdu_flags_agree_num,
          { "Agreement Number",    "mstp.agree_flags.agreement_num",
        FT_UINT8, BASE_DEC, NULL, 0x03,
            NULL, HFILL } },
        { &hf_bpdu_flags_dagree_num,
          { "Disagreement Number",    "mstp.agree_flags.dagreement_num",
        FT_UINT8, BASE_DEC, NULL, 0x0C,
            NULL, HFILL } },
        { &hf_bpdu_flags_agree_valid,
          { "Agreement Valid Flag",    "mstp.agree_flags.agreement_valid",
        FT_BOOLEAN, 8, TFS(&tfs_yes_no), 0x10,
            NULL, HFILL } },
        { &hf_bpdu_flags_restricted_role,
          { "Restricted Role",    "mstp.agree_flags.rest_role",
        FT_BOOLEAN, 8, TFS(&tfs_yes_no), 0x20,
            NULL, HFILL } },
        { &hf_bpdu_spt_agreement_digest,
          { "Agreement Digest",    "mstp.agreement_digest",
        FT_BYTES, BASE_NONE, NULL, 0x0,
            NULL, HFILL } },
        { &hf_bpdu_agreement_digest_format_id,
          { "Agreement Digest Format Id", "bpdu.agreement_digest_format_id",
        FT_UINT8, BASE_DEC, NULL, 0xF0,
            NULL, HFILL }},
        { &hf_bpdu_agreement_digest_format_capabilities,
          { "Agreement Digest Format Capabilities", "bpdu.agreement_digest_format_capabilities",
        FT_UINT8, BASE_DEC, NULL, 0x0F,
            NULL, HFILL }},
        { &hf_bpdu_agreement_digest_convention_id,
          { "Agreement Digest Convention Id", "bpdu.agreement_digest_convention_id",
        FT_UINT8, BASE_DEC, NULL, 0xF0,
            NULL, HFILL }},
        { &hf_bpdu_agreement_digest_convention_capabilities,
          { "Agreement Digest Convention Capabilities", "bpdu.agreement_digest_convention_capabilities",
        FT_UINT8, BASE_DEC, NULL, 0x0F,
            NULL, HFILL }},
        { &hf_bpdu_agreement_digest_edge_count,
          { "Agreement Digest Edge Count", "bpdu.agreement_digest_edge_count",
        FT_UINT16, BASE_DEC, NULL, 0x0,
            NULL, HFILL }},
  };
  static gint *ett[] = {
    &ett_bpdu,
    &ett_bpdu_flags,
    &ett_root_id,
    &ett_bridge_id,
    &ett_mstp,
    &ett_msti,
    &ett_cist_bridge_id,
    &ett_spt,
    &ett_aux_mcid,
    &ett_agreement,
    &ett_bpdu_pvst_tlv
  };

  static ei_register_info ei[] = {
  { &ei_pvst_tlv_length_invalid,
    { "stp.pvst.tlvlen.invalid", PI_MALFORMED, PI_ERROR,
      "Indicated length is not valid for this record type", EXPFILL }},

  { &ei_pvst_tlv_origvlan_missing,
    { "stp.pvst.origvlan.missing", PI_MALFORMED, PI_ERROR,
      "Originating (PVID) VLAN TLV is missing or corrupt", EXPFILL }},

  { &ei_pvst_tlv_truncated,
    { "stp.pvst.tlv.truncated", PI_MALFORMED, PI_ERROR,
      "TLV record is truncated prematurely", EXPFILL }},

  { &ei_pvst_tlv_unknown,
    { "stp.pvst.tlv.unknown", PI_UNDECODED, PI_COMMENT,
      "TLV type is unknown", EXPFILL }},

  { &ei_bpdu_version_support,
    { "bpdu.version_support", PI_PROTOCOL, PI_WARN,
      "This version of Wireshark only knows about versions 0, 2, 3 & 4", EXPFILL }},

  { &ei_bpdu_type,
    { "stp.type.unknown", PI_PROTOCOL, PI_WARN,
      "Unknown BPDU type data", EXPFILL }},
  };

  module_t *bpdu_module;
  expert_module_t *expert_bpdu;

  proto_bpdu = proto_register_protocol("Spanning Tree Protocol", "STP", "stp");
  proto_register_field_array(proto_bpdu, hf, array_length(hf));
  proto_register_subtree_array(ett, array_length(ett));

  bpdu_handle = register_dissector("bpdu", dissect_bpdu_generic, proto_bpdu);
  bpdu_cisco_handle = register_dissector("bpdu_cisco", dissect_bpdu_cisco, proto_bpdu);

  expert_bpdu = expert_register_protocol(proto_bpdu);
  expert_register_field_array(expert_bpdu, ei, array_length(ei));

  bpdu_module = prefs_register_protocol(proto_bpdu, NULL);
  prefs_register_bool_preference(bpdu_module, "use_system_id_extension",
    "Use 802.1t System ID Extensions",
    "Whether the BPDU dissector should use 802.1t System ID Extensions when dissecting the Bridge Identifier",
    &bpdu_use_system_id_extensions);
}

void
proto_reg_handoff_bpdu(void)
{
  /*
   * Get handle for the GVRP dissector.
   */
  gvrp_handle = find_dissector("gvrp");

  /*
   * Get handle for the GMRP dissector.
   */
  gmrp_handle = find_dissector_add_dependency("gmrp", proto_bpdu);

  dissector_add_uint("llc.dsap", SAP_BPDU, bpdu_handle);
  dissector_add_uint("chdlc.protocol", CHDLCTYPE_BPDU, bpdu_handle);
  dissector_add_uint("ethertype", ETHERTYPE_STP, bpdu_handle);
  dissector_add_uint("llc.cisco_pid", CISCO_PID_RLQ_REQ, bpdu_handle); /* Cisco's RLQ is just plain STP */
  dissector_add_uint("llc.cisco_pid", CISCO_PID_RLQ_RESP, bpdu_handle); /* Cisco's RLQ is just plain STP */
  dissector_add_uint("llc.cisco_pid", CISCO_PID_VLAN_BRIDGE, bpdu_handle); /* Cisco's VLAN-bridge STP is just plain STP */
  dissector_add_uint("llc.cisco_pid", CISCO_PID_PVSTPP, bpdu_cisco_handle); /* Handle Cisco's (R)PVST+ TLV extensions */
}

/*
 * Editor modelines  -  https://www.wireshark.org/tools/modelines.html
 *
 * Local Variables:
 * c-basic-offset: 2
 * tab-width: 8
 * indent-tabs-mode: nil
 * End:
 *
 * ex: set shiftwidth=2 tabstop=8 expandtab:
 * :indentSize=2:tabSize=8:noTabs=true:
 */