/* packet-bpdu.c
 * Routines for BPDU (Spanning Tree Protocol) disassembly
 *
 * $Id: packet-bpdu.c 32735 2010-05-10 15:54:57Z wmeier $
 *
 * Copyright 1999 Christophe Tronche <ch.tronche@computer.org>
 *
 * Wireshark - Network traffic analyzer
 * By Gerald Combs <gerald@wireshark.org>
 * Copyright 1998 Gerald Combs
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
# include "config.h"
#endif

#include <glib.h>
#include <epan/packet.h>
#include <epan/llcsaps.h>
#include <epan/ppptypes.h>
#include <epan/chdlctypes.h>
#include <epan/etypes.h>
#include <epan/addr_resolv.h>
#include <epan/prefs.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 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

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_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_remaining_hops = -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 gboolean bpdu_use_system_id_extensions = TRUE;

static dissector_handle_t gvrp_handle;
static dissector_handle_t gmrp_handle;
static dissector_handle_t data_handle;

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

#define APPEND_BOOLEAN_FLAG(flag, item, string)         \
  if(flag){                                             \
    if(item)						\
      proto_item_append_text(item, string, sep);	\
    sep = cont_sep;                                     \
  }

static void
dissect_bpdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  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 guint8  *root_identifier_mac;
  gchar   *root_identifier_mac_str;
  guint32 root_path_cost;
  guint16 bridge_identifier_bridge_priority;
  guint16 bridge_identifier_system_id_extension = 0;
  const guint8  *bridge_identifier_mac;
  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;
  guint8 config_format_selector;
  guint16 cist_bridge_identifier_bridge_priority;
  guint16 cist_bridge_identifier_system_id_extension = 0;
  const guint8  *cist_bridge_identifier_mac;
  gchar   *cist_bridge_identifier_mac_str;
  guint16 msti_mstid;
  guint32 msti_regional_root_mstid, msti_regional_root_priority;
  const guint8  *msti_regional_root_mac;
  gchar   *msti_regional_root_mac_str;
  guint16 msti_bridge_identifier_priority, msti_port_identifier_priority;
  const guint8  *msti_bridge_identifier_mac;
  gchar   *msti_bridge_identifier_mac_str;
  int   total_msti_length, offset, msti, msti_format;

  proto_tree *bpdu_tree;
  proto_tree *mstp_tree, *msti_tree;
  proto_item *bpdu_item;
  proto_item *mstp_item, *msti_item;
  proto_tree *flags_tree;
  proto_item *flags_item;
  proto_tree *root_id_tree;
  proto_item *root_id_item;
  proto_tree *bridge_id_tree;
  proto_item *bridge_id_item;
  proto_tree *cist_bridge_id_tree;
  proto_item *cist_bridge_id_item;
  proto_item *hidden_item;
  const char *sep;

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

      switch (dstaddr[5]) {

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

      case 0x21:
        /* for GVRP */
        call_dissector(gvrp_handle, tvb, pinfo, tree);
        return;
      }

      pinfo->current_proto = "GARP";

      if (check_col(pinfo->cinfo, COL_PROTOCOL)) {
        col_set_str(pinfo->cinfo, COL_PROTOCOL, "GARP");
        /* Generic Attribute Registration Protocol */
      }

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

      return;
    }
  }

  if (check_col(pinfo->cinfo, COL_PROTOCOL)) {
    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 = tvb_get_ptr(tvb, BPDU_ROOT_IDENTIFIER + 2, 6);
    root_identifier_mac_str = ether_to_str(root_identifier_mac);
    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 = NULL;
    root_identifier_mac_str = NULL;
    root_path_cost = 0;
    port_identifier = 0;
    break;
  }

  if (check_col(pinfo->cinfo, COL_INFO)) {
    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,
                     "%cST. %sRoot = %d/%d/%s  Cost = %d  Port = 0x%04x",
                     protocol_version_identifier == 3 ? 'M':'R',
                     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,
                     "%cST. %sRoot = %d/%s  Cost = %d  Port = 0x%04x",
                     protocol_version_identifier == 3 ? 'M':'R',
                     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;
    }
  }

  if (tree) {
    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_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:
      break;

    default:
      proto_tree_add_text(bpdu_tree, tvb, BPDU_VERSION_IDENTIFIER, 1,
                          "   (Warning: this version of Wireshark only knows about versions 0, 2 & 3)");
      break;
    }
    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 */
      proto_tree_add_text(bpdu_tree, tvb, BPDU_TYPE + 1, -1,
                          "Unknown BPDU type data");
      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 = tvb_get_ptr(tvb, BPDU_BRIDGE_IDENTIFIER + 2, 6);
    bridge_identifier_mac_str = ether_to_str(bridge_identifier_mac);

    flags_item = proto_tree_add_uint(bpdu_tree, hf_bpdu_flags, tvb,
                                     BPDU_FLAGS, 1, flags);
    flags_tree = proto_item_add_subtree(flags_item, ett_bpdu_flags);
    sep = initial_sep;
    APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TCACK, flags_item,
                        "%sTopology Change Acknowledgment");
    proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tcack, tvb,
                           BPDU_FLAGS, 1, flags);
    if (bpdu_type == BPDU_TYPE_RST) {
      APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_AGREEMENT, flags_item,
                          "%sAgreement");
      proto_tree_add_boolean(flags_tree, hf_bpdu_flags_agreement, tvb,
                             BPDU_FLAGS, 1, flags);
      APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_FORWARDING, flags_item,
                          "%sForwarding");
      proto_tree_add_boolean(flags_tree, hf_bpdu_flags_forwarding, tvb,
                             BPDU_FLAGS, 1, flags);
      APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_LEARNING, flags_item,
                          "%sLearning");
      proto_tree_add_boolean(flags_tree, hf_bpdu_flags_learning, tvb,
                             BPDU_FLAGS, 1, flags);
      if (flags_item) {
        guint8 port_role;

        port_role = (flags & BPDU_FLAGS_PORT_ROLE_MASK) >> BPDU_FLAGS_PORT_ROLE_SHIFT;
        proto_item_append_text(flags_item, "%sPort Role: %s", sep,
                               val_to_str(port_role, role_vals,
                                          "Unknown (%u)"));
      }
      sep = cont_sep;
      proto_tree_add_uint(flags_tree, hf_bpdu_flags_port_role, tvb,
                          BPDU_FLAGS, 1, flags);
      APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_PROPOSAL, flags_item,
                          "%sProposal");
      proto_tree_add_boolean(flags_tree, hf_bpdu_flags_proposal, tvb,
                             BPDU_FLAGS, 1, flags);
    }
    APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TC, flags_item,
                        "%sTopology Change");
    proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tc, tvb,
                           BPDU_FLAGS, 1, flags);
    if (sep != initial_sep) {
      /* We put something in; put in the terminating ")" */
      proto_item_append_text(flags_item, ")");
    }

    /* add Identifier with format based on preference value
     * bpdu_use_system_id_extensions
     * */
    if (bpdu_use_system_id_extensions) {
      root_id_item = proto_tree_add_text(bpdu_tree, tvb,
                          BPDU_ROOT_IDENTIFIER, 8,
			  "Root Identifier: %d / %d / %s",
			  root_identifier_bridge_priority,
			  root_identifier_system_id_extension,
			  root_identifier_mac_str);
      root_id_tree = proto_item_add_subtree(root_id_item, ett_root_id);
      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_ether_format_value(root_id_tree, hf_bpdu_root_mac,
                              tvb, BPDU_ROOT_IDENTIFIER + 2, 6,
                              root_identifier_mac,
                              "%s", root_identifier_mac_str);
    } else {
      root_id_item = proto_tree_add_text(bpdu_tree, tvb,
                          BPDU_ROOT_IDENTIFIER, 8,
			  "Root Identifier: %d / %s",
			  root_identifier_bridge_priority,
			  root_identifier_mac_str);
      root_id_tree = proto_item_add_subtree(root_id_item, ett_root_id);
      proto_tree_add_uint(root_id_tree, hf_bpdu_root_prio, tvb,
			      BPDU_ROOT_IDENTIFIER , 2, 
			      root_identifier_bridge_priority);
      proto_tree_add_ether_format_value(root_id_tree, hf_bpdu_root_mac,
                              tvb, BPDU_ROOT_IDENTIFIER + 2, 6,
                              root_identifier_mac,
                              "%s", root_identifier_mac_str);
    }
    /* 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_item = proto_tree_add_text(bpdu_tree, tvb,
                          BPDU_BRIDGE_IDENTIFIER, 8,
			  "Bridge Identifier: %d / %d / %s",
			  bridge_identifier_bridge_priority,
			  bridge_identifier_system_id_extension,
			  bridge_identifier_mac_str);
      bridge_id_tree = proto_item_add_subtree(bridge_id_item, ett_bridge_id);
      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_ether_format_value(bridge_id_tree, hf_bpdu_bridge_mac,
                              tvb, BPDU_BRIDGE_IDENTIFIER + 2, 6,
                              bridge_identifier_mac,
                              "%s", bridge_identifier_mac_str);
    } else {
      bridge_id_item = proto_tree_add_text(bpdu_tree, tvb, 
                          BPDU_BRIDGE_IDENTIFIER, 8,
			  "Bridge Identifier: %d / %s",
			  bridge_identifier_bridge_priority,
			  bridge_identifier_mac_str);
      bridge_id_tree = proto_item_add_subtree(bridge_id_item, ett_bridge_id);
      proto_tree_add_uint(bridge_id_tree, hf_bpdu_bridge_prio, tvb,
                              BPDU_BRIDGE_IDENTIFIER , 2, 
			      bridge_identifier_bridge_priority);
      proto_tree_add_ether_format_value(bridge_id_tree, hf_bpdu_bridge_mac,
                              tvb, BPDU_BRIDGE_IDENTIFIER + 2, 6,
                              bridge_identifier_mac,
                              "%s", bridge_identifier_mac_str);
    }
    /* 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) {
      /* 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;
	}

      }
      set_actual_length(tvb, BPDU_MSTI + total_msti_length);

      mstp_item = proto_tree_add_text(bpdu_tree, tvb, BPDU_VERSION_3_LENGTH,
                                      -1, "MST Extension");
      mstp_tree = proto_item_add_subtree(mstp_item, ett_mstp);

      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_format_selector, tvb,
                          BPDU_MST_CONFIG_FORMAT_SELECTOR, 1, FALSE);
      proto_tree_add_item(mstp_tree, hf_bpdu_mst_config_name, tvb,
                          BPDU_MST_CONFIG_NAME, 32, FALSE);

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

      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, FALSE);

	cist_bridge_identifier_bridge_priority = tvb_get_ntohs(tvb,BPDU_CIST_BRIDGE_IDENTIFIER);
	cist_bridge_identifier_mac = tvb_get_ptr(tvb, BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6);
	cist_bridge_identifier_mac_str = ether_to_str(cist_bridge_identifier_mac);

        /* 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_item = proto_tree_add_text(mstp_tree, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                              "CIST Bridge Identifier: %d / %d / %s",
                              cist_bridge_identifier_bridge_priority,
                              cist_bridge_identifier_system_id_extension,
                              cist_bridge_identifier_mac_str);
          cist_bridge_id_tree = proto_item_add_subtree(cist_bridge_id_item, ett_cist_bridge_id);
          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_ether_format_value(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac,
                                  tvb, BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                                  cist_bridge_identifier_mac,
                                  "%s", cist_bridge_identifier_mac_str);
        } else {
          cist_bridge_id_item = proto_tree_add_text(mstp_tree, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                              "CIST Bridge Identifier: %d / %s",
                              cist_bridge_identifier_bridge_priority,
                              cist_bridge_identifier_mac_str);
          cist_bridge_id_tree = proto_item_add_subtree(cist_bridge_id_item, ett_cist_bridge_id);
          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_ether_format_value(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac,
                                  tvb, BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                                  cist_bridge_identifier_mac,
                                  "%s", cist_bridge_identifier_mac_str);
        }
        /* 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 = tvb_get_ptr(tvb, ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6);
	cist_bridge_identifier_mac_str = ether_to_str(cist_bridge_identifier_mac);

        /* 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_item = proto_tree_add_text(mstp_tree, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                              "CIST Bridge Identifier: %d / %d / %s",
                              cist_bridge_identifier_bridge_priority,
                              cist_bridge_identifier_system_id_extension,
                              cist_bridge_identifier_mac_str);
          cist_bridge_id_tree = proto_item_add_subtree(cist_bridge_id_item, ett_cist_bridge_id);
          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_ether_format_value(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac,
                                  tvb, ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                                  cist_bridge_identifier_mac,
                                  "%s", cist_bridge_identifier_mac_str);
        } else {
          cist_bridge_id_item = proto_tree_add_text(mstp_tree, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER, 8,
                              "CIST Bridge Identifier: %d / %s",
                              cist_bridge_identifier_bridge_priority,
                              cist_bridge_identifier_mac_str);
          cist_bridge_id_tree = proto_item_add_subtree(cist_bridge_id_item, ett_cist_bridge_id);
          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_ether_format_value(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac,
                                  tvb, ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                                  cist_bridge_identifier_mac,
                                  "%s", cist_bridge_identifier_mac_str);
        }
        /* 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, FALSE);

	break;
      }

      proto_tree_add_item(mstp_tree, hf_bpdu_cist_remaining_hops, tvb,
                          BPDU_CIST_REMAINING_HOPS, 1, FALSE);
      /* MSTI messages */
      offset = BPDU_MSTI;
      msti = 1;
      while (total_msti_length > 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 = tvb_get_ptr(tvb, offset+ MSTI_REGIONAL_ROOT + 2, 6);
	  msti_regional_root_mac_str = ether_to_str(msti_regional_root_mac);

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

	  /* flags */
	  flags = tvb_get_guint8(tvb, offset+MSTI_FLAGS);
	  flags_item = proto_tree_add_uint(msti_tree, hf_bpdu_msti_flags, tvb,
					   offset+MSTI_FLAGS, 1, flags);
	  flags_tree = proto_item_add_subtree(flags_item, ett_bpdu_flags);

	  sep = initial_sep;
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TCACK, flags_item, "%sMaster");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tcack, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_AGREEMENT, flags_item, "%sAgreement");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_agreement, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_FORWARDING, flags_item, "%sForwarding");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_forwarding, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_LEARNING, flags_item, "%sLearning");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_learning, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  if (flags_item) {
	    guint8 port_role;
	    port_role = (flags & BPDU_FLAGS_PORT_ROLE_MASK) >> BPDU_FLAGS_PORT_ROLE_SHIFT;
	    proto_item_append_text(flags_item, "%sPort Role: %s", sep,
				   val_to_str(port_role, role_vals,
				   "Unknown (%u)"));
	  }
	  proto_tree_add_uint(flags_tree, hf_bpdu_flags_port_role, tvb,
			      offset+MSTI_FLAGS, 1, flags);
	  sep = cont_sep;
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_PROPOSAL, flags_item, "%sProposal");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_proposal, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TC, flags_item, "%sTopology Change");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tc, tvb,
				 offset+MSTI_FLAGS, 1, flags);
	  if (sep != initial_sep) { 	      /* We put something in; put in the terminating ")" */
	    proto_item_append_text(flags_item, ")");
	  }

	  /* pri, MSTID, Regional root */
	  hidden_item = proto_tree_add_ether(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
				      offset + MSTI_REGIONAL_ROOT + 2, 6,
				      msti_regional_root_mac);
	  PROTO_ITEM_SET_HIDDEN(hidden_item);
	  proto_tree_add_text(msti_tree, tvb, offset + MSTI_REGIONAL_ROOT, 8,
			      "MSTID %d, priority %d Root Identifier %s",
			      msti_regional_root_mstid,
			      msti_regional_root_priority,
			      msti_regional_root_mac_str);


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

	  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, FALSE);

	  total_msti_length -= 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 = tvb_get_ptr(tvb, offset+ ALT_MSTI_REGIONAL_ROOT + 2, 6);
	  msti_regional_root_mac_str = ether_to_str(msti_regional_root_mac);

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

	  msti_mstid = tvb_get_ntohs(tvb,  offset+ ALT_MSTI_MSTID);
	  proto_tree_add_text(msti_tree, tvb, offset+ALT_MSTI_MSTID, 2, 
			      "MSTID: %d", msti_mstid);

	  /* flags */
	  flags = tvb_get_guint8(tvb, offset+ALT_MSTI_FLAGS);
	  flags_item = proto_tree_add_uint(msti_tree, hf_bpdu_msti_flags, tvb,
					   offset+ALT_MSTI_FLAGS, 1, flags);
	  flags_tree = proto_item_add_subtree(flags_item, ett_bpdu_flags);

	  sep = initial_sep;
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TCACK, flags_item, "%sMaster");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tcack, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_AGREEMENT, flags_item, "%sAgreement");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_agreement, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_FORWARDING, flags_item, "%sForwarding");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_forwarding, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_LEARNING, flags_item, "%sLearning");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_learning, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  if (flags_item) {
	    guint8 port_role;
	    port_role = (flags & BPDU_FLAGS_PORT_ROLE_MASK) >> BPDU_FLAGS_PORT_ROLE_SHIFT;
	    proto_item_append_text(flags_item, "%sPort Role: %s", sep,
				   val_to_str(port_role, role_vals,
				   "Unknown (%u)"));
	  }
	  proto_tree_add_uint(flags_tree, hf_bpdu_flags_port_role, tvb,
			      offset+ALT_MSTI_FLAGS, 1, flags);
	  sep = cont_sep;
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_PROPOSAL, flags_item, "%sProposal");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_proposal, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  APPEND_BOOLEAN_FLAG(flags & BPDU_FLAGS_TC, flags_item, "%sTopology Change");
	  proto_tree_add_boolean(flags_tree, hf_bpdu_flags_tc, tvb,
				 offset+ALT_MSTI_FLAGS, 1, flags);
	  if (sep != initial_sep) { 	      /* We put something in; put in the terminating ")" */
	    proto_item_append_text(flags_item, ")");
	  }

	  /* pri, MSTID, Regional root */
	  hidden_item = proto_tree_add_ether(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
				      offset + ALT_MSTI_REGIONAL_ROOT + 2, 6,
				      msti_regional_root_mac);
	  PROTO_ITEM_SET_HIDDEN(hidden_item);
	  proto_tree_add_text(msti_tree, tvb, offset + ALT_MSTI_REGIONAL_ROOT, 8,
			      "MSTI Regional Root Identifier: %d / %d / %s",
			      msti_regional_root_mstid,
			      msti_regional_root_priority,
			      msti_regional_root_mac_str);


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

	  msti_bridge_identifier_priority = tvb_get_ntohs(tvb, offset+ALT_MSTI_BRIDGE_IDENTIFIER);
	  msti_bridge_identifier_mac = tvb_get_ptr(tvb, offset+ALT_MSTI_BRIDGE_IDENTIFIER + 2, 6);
	  msti_bridge_identifier_mac_str = ether_to_str(msti_bridge_identifier_mac);
	  proto_tree_add_text(msti_tree, tvb, offset+ALT_MSTI_BRIDGE_IDENTIFIER, 8,
			      "MSTI Bridge Identifier: %d / %d / %s",
			      msti_bridge_identifier_priority & 0x0fff,
			      msti_bridge_identifier_priority & 0xf000,
			      msti_bridge_identifier_mac_str);

	  msti_port_identifier_priority = tvb_get_ntohs(tvb, offset+ALT_MSTI_PORT_IDENTIFIER);
	  proto_tree_add_uint(msti_tree, hf_bpdu_msti_port_id, tvb, 
			      offset+ALT_MSTI_PORT_IDENTIFIER, 2, msti_port_identifier_priority);

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

	  total_msti_length -= ALT_MSTI_MESSAGE_SIZE;
	  offset += ALT_MSTI_MESSAGE_SIZE;
	  break;

	}
        msti++;
      }
    }
  }
}

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_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_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_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 }},

  };
  static gint *ett[] = {
    &ett_bpdu,
    &ett_bpdu_flags,
    &ett_root_id,
    &ett_bridge_id,
    &ett_mstp,
    &ett_msti,
    &ett_cist_bridge_id
  };
  module_t *bpdu_module;

  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));

  register_dissector("bpdu", dissect_bpdu, proto_bpdu);

  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)
{
  dissector_handle_t bpdu_handle;

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

  /*
   * Get handle for the GMRP dissector.
   */
  gmrp_handle = find_dissector("gmrp");
  data_handle = find_dissector("data");

  bpdu_handle = find_dissector("bpdu");
  dissector_add("llc.dsap", SAP_BPDU, bpdu_handle);
  dissector_add("chdlctype", CHDLCTYPE_BPDU, bpdu_handle);
  dissector_add("llc.cisco_pid", 0x010b, bpdu_handle);
  dissector_add("ethertype", ETHERTYPE_STP, bpdu_handle);
}
