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packet-bpdu.c

/* packet-bpdu.c
 * Routines for BPDU (Spanning Tree Protocol) disassembly
 *
 * $Id: packet-bpdu.c 23252 2007-10-23 05:50:00Z etxrab $
 *
 * 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 <stdio.h>
#include <string.h>
#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>

/* 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_mac = -1;
static int hf_bpdu_root_cost = -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_identifier_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_mstp = -1;
static gint ett_msti = -1;

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;
  const guint8  *root_identifier_mac;
  gchar   *root_identifier_mac_str;
  guint32 root_path_cost;
  guint16 bridge_identifier_bridge_priority;
  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;
  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;
  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)) {

      protocol_identifier = tvb_get_ntohs(tvb, BPDU_IDENTIFIER);

      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 */
  }
  if (check_col(pinfo->cinfo, COL_INFO)) {
    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);
    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:
      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:
      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);
    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, ")");
    }

    proto_tree_add_ether_hidden(bpdu_tree, hf_bpdu_root_mac, tvb,
                                BPDU_ROOT_IDENTIFIER + 2, 6,
                                root_identifier_mac);
    proto_tree_add_text(bpdu_tree, tvb, BPDU_ROOT_IDENTIFIER, 8,
                        "Root Identifier: %d / %s",
                        root_identifier_bridge_priority,
                        root_identifier_mac_str);
    proto_tree_add_uint(bpdu_tree, hf_bpdu_root_cost, tvb,
                        BPDU_ROOT_PATH_COST, 4, root_path_cost);
    proto_tree_add_text(bpdu_tree, tvb, BPDU_BRIDGE_IDENTIFIER, 8,
                        "Bridge Identifier: %d / %s",
                        bridge_identifier_bridge_priority,
                        bridge_identifier_mac_str);
    proto_tree_add_ether_hidden(bpdu_tree, hf_bpdu_bridge_mac, tvb,
                                BPDU_BRIDGE_IDENTIFIER + 2, 6,
                                bridge_identifier_mac);
    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);
      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);
      proto_tree_add_ether_hidden(mstp_tree, hf_bpdu_cist_bridge_identifier_mac, tvb,
                            BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                            cist_bridge_identifier_mac);
      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);
      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);
      proto_tree_add_ether_hidden(mstp_tree, hf_bpdu_cist_bridge_identifier_mac, tvb,
                            ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6,
                            cist_bridge_identifier_mac);

      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 */
        proto_tree_add_ether_hidden(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                              offset + MSTI_REGIONAL_ROOT + 2, 6,
                              msti_regional_root_mac);
        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 */
        proto_tree_add_ether_hidden(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                              offset + ALT_MSTI_REGIONAL_ROOT + 2, 6,
                              msti_regional_root_mac);
        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++;
      }
    }
  }
}

static const true_false_string yesno = {
      "Yes",
      "No"
};

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,
            "", HFILL }},
    { &hf_bpdu_version_id,
      { "Protocol Version Identifier",    "stp.version",
      FT_UINT8,   BASE_DEC,   VALS(&version_id_vals), 0x0,
            "", HFILL }},
    { &hf_bpdu_type,
      { "BPDU Type",                "stp.type",
      FT_UINT8,   BASE_HEX,   VALS(&bpdu_type_vals),  0x0,
            "", HFILL }},
    { &hf_bpdu_flags,
      { "BPDU flags",               "stp.flags",
      FT_UINT8,   BASE_HEX,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_flags_tcack,
      { "Topology Change Acknowledgment",  "stp.flags.tcack",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_TCACK,
            "", HFILL }},
    { &hf_bpdu_flags_agreement,
      { "Agreement",                "stp.flags.agreement",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_AGREEMENT,
            "", HFILL }},
    { &hf_bpdu_flags_forwarding,
      { "Forwarding",               "stp.flags.forwarding",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_FORWARDING,
            "", HFILL }},
    { &hf_bpdu_flags_learning,
      { "Learning",                 "stp.flags.learning",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_LEARNING,
            "", HFILL }},
    { &hf_bpdu_flags_port_role,
      { "Port Role",                "stp.flags.port_role",
      FT_UINT8,   BASE_DEC,   VALS(role_vals),  BPDU_FLAGS_PORT_ROLE_MASK,
            "", HFILL }},
    { &hf_bpdu_flags_proposal,
      { "Proposal",                 "stp.flags.proposal",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_PROPOSAL,
            "", HFILL }},
    { &hf_bpdu_flags_tc,
      { "Topology Change",          "stp.flags.tc",
      FT_BOOLEAN, 8,          TFS(&yesno),      BPDU_FLAGS_TC,
            "", HFILL }},
    { &hf_bpdu_root_mac,
      { "Root Identifier",          "stp.root.hw",
      FT_ETHER,   BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_root_cost,
      { "Root Path Cost",           "stp.root.cost",
      FT_UINT32,  BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_bridge_mac,
      { "Bridge Identifier",        "stp.bridge.hw",
      FT_ETHER,   BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_port_id,
      { "Port identifier",          "stp.port",
      FT_UINT16,  BASE_HEX,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msg_age,
      { "Message Age",              "stp.msg_age",
      FT_DOUBLE,  BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_max_age,
      { "Max Age",                  "stp.max_age",
      FT_DOUBLE,  BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_hello_time,
      { "Hello Time",               "stp.hello",
      FT_DOUBLE,  BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_forward_delay,
      { "Forward Delay",            "stp.forward",
      FT_DOUBLE,  BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_version_1_length,
      { "Version 1 Length",         "stp.version_1_length",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_version_3_length,
      { "Version 3 Length",         "mstp.version_3_length",
      FT_UINT16,  BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_mst_config_format_selector,
      { "MST Config ID format selector",  "mstp.config_format_selector",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_mst_config_name,
      { "MST Config name",          "mstp.config_name",
      FT_STRINGZ, BASE_NONE,  NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_mst_config_revision_level,
      { "MST Config revision",            "mstp.config_revision_level",
      FT_UINT16,  BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_mst_config_digest,
      { "MST Config digest",        "mstp.config_digest",
      FT_BYTES,   BASE_DEC,   NULL, 0x0,
            "", 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,
            "", HFILL }},
    { &hf_bpdu_cist_bridge_identifier_mac,
      { "CIST Bridge Identifier",         "mstp.cist_bridge.hw",
      FT_ETHER,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_cist_remaining_hops,
      { "CIST Remaining hops",            "mstp.cist_remaining_hops",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_flags,
      { "MSTI flags",               "mstp.msti.flags",
      FT_UINT8,   BASE_HEX,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_regional_root_mac,
      { "Regional Root",            "mstp.msti.root.hw",
      FT_ETHER,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_internal_root_path_cost,
      { "Internal root path cost",        "mstp.msti.root_cost",
      FT_UINT32,  BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_bridge_identifier_priority,
      { "Bridge Identifier Priority",           "mstp.msti.bridge_priority",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_port_identifier_priority,
      { "Port identifier priority",       "mstp.msti.port_priority",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_port_id,
      { "Port identifier",          "mstp.msti.port",
      FT_UINT16,  BASE_HEX,   NULL, 0x0,
            "", HFILL }},
    { &hf_bpdu_msti_remaining_hops,
      { "Remaining hops",           "mstp.msti.remaining_hops",
      FT_UINT8,   BASE_DEC,   NULL, 0x0,
            "", HFILL }},

  };
  static gint *ett[] = {
    &ett_bpdu,
    &ett_bpdu_flags,
    &ett_mstp,
    &ett_msti
  };

  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);
}

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);
}

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