/* packet-bpdu.c
 * Routines for BPDU (Spanning Tree Protocol) disassembly
 *
 * $Id$
 *
 * 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#include "config.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>
#include <epan/prefs.h>
#include <epan/expert.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_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 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_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 gboolean bpdu_use_system_id_extensions = TRUE;

static dissector_handle_t gvrp_handle;
static dissector_handle_t gmrp_handle;

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[] = ", ";

#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, gboolean is_bpdu_pvst);

static void
dissect_bpdu_cisco(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  dissect_bpdu(tvb, pinfo, tree, TRUE);
}

static void
dissect_bpdu_generic(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
  dissect_bpdu(tvb, pinfo, tree, FALSE);
}

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);

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

    tlv_tree = proto_item_add_subtree(ti, ett_bpdu_pvst_tlv);
    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;
  guint16 msti_mstid;
  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;
  const gchar *msti_bridge_identifier_mac_str;
  int   total_msti_length, offset, msti, msti_format;
  int   msti_length_remaining;
  guint8 agree_num = 0, dagree_num = 0;

  int spt_offset = 0;
  guint16 spt_edge_count = 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 *mstp_item, *msti_item, *spt_item = NULL, *aux_mcid_item = NULL, *agreement_item = NULL;
  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 = (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;
      }

      pinfo->current_proto = "GARP";

      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;
  }

  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:
    case 4:
      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 & 4)");
      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_str = tvb_ether_to_str(tvb, BPDU_BRIDGE_IDENTIFIER + 2);

    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_item(root_id_tree, hf_bpdu_root_mac, tvb,
                          BPDU_ROOT_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);

    } 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_item(root_id_tree, hf_bpdu_root_mac, tvb,
                          BPDU_ROOT_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
    }
    /* 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_item(bridge_id_tree, hf_bpdu_bridge_mac, tvb,
                          BPDU_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
    } 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_item(bridge_id_tree, hf_bpdu_bridge_mac, tvb,
                          BPDU_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
    }
    /* 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_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, 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_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_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);

        } 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_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
        }
        /* 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_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_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
        } 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_item(cist_bridge_id_tree, hf_bpdu_cist_bridge_mac, tvb,
                              ALT_BPDU_CIST_BRIDGE_IDENTIFIER + 2, 6, ENC_BIG_ENDIAN);
        }
        /* 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_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_item(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                                            offset + MSTI_REGIONAL_ROOT + 2, 6, ENC_BIG_ENDIAN);

          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, 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_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_item(msti_tree, hf_bpdu_msti_regional_root_mac, tvb,
                                            offset + ALT_MSTI_REGIONAL_ROOT + 2, 6, ENC_BIG_ENDIAN);

          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, ENC_BIG_ENDIAN);

          msti_bridge_identifier_priority = tvb_get_ntohs(tvb, offset+ALT_MSTI_BRIDGE_IDENTIFIER);
          msti_bridge_identifier_mac_str = tvb_ether_to_str(tvb, ALT_MSTI_BRIDGE_IDENTIFIER + 2);

          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, 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) {
          spt_item = proto_tree_add_text(bpdu_tree, tvb,
                                         bpdu_version_4_length, -1, "SPT Extension");

          spt_tree = proto_item_add_subtree(spt_item, ett_spt);

          spt_offset = (bpdu_version_4_length + 2);

          /* Aux MCID: */

          aux_mcid_item = proto_tree_add_text(spt_tree, tvb, spt_offset,
                                              MCID_LEN, "MCID Data");
          aux_mcid_tree = proto_item_add_subtree(aux_mcid_item, ett_aux_mcid);

          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_item = proto_tree_add_text(spt_tree, tvb, spt_offset,
                                               -1, "Agreement Data");
          agreement_tree = proto_item_add_subtree(agreement_item, ett_agreement);

          spt_agree_data = tvb_get_guint8(tvb, spt_offset);

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

          proto_tree_add_uint(agreement_tree, hf_bpdu_flags_agree_num,
                              tvb, spt_offset, 1, spt_agree_data);
          sep = cont_sep;

          if (agreement_item) {
            dagree_num = ((spt_agree_data & 0x0C) >> 2);
            proto_item_append_text(agreement_item, "%sDAN: %d", sep, dagree_num);
          }
          proto_tree_add_uint(agreement_tree, hf_bpdu_flags_dagree_num,
                              tvb, spt_offset, 1, spt_agree_data);

          proto_tree_add_boolean(agreement_tree, hf_bpdu_flags_agree_valid,
                                 tvb, spt_offset, 1, spt_agree_data);

          proto_tree_add_boolean(agreement_tree, hf_bpdu_flags_restricted_role,
                                 tvb, spt_offset, 1, spt_agree_data);

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

          spt_agree_data = tvb_get_guint8(tvb, spt_offset);

          proto_tree_add_text(agreement_tree, tvb, spt_offset, 1,
                              "Agreement Digest Format Id: %d",
                              (spt_agree_data & 0xf0) >> 4);
          proto_tree_add_text(agreement_tree, tvb, spt_offset, 1,
                              "Agreement Digest Format Capabilities: %d",
                              (spt_agree_data & 0x0f));
          spt_offset += 1;

          spt_agree_data = tvb_get_guint8(tvb, spt_offset);

          proto_tree_add_text(agreement_tree, tvb, spt_offset, 1,
                              "Agreement Digest Convention Id: %d",
                              (spt_agree_data & 0xf0) >> 4);
          proto_tree_add_text(agreement_tree, tvb, spt_offset, 1,
                              "Agreement Digest Convention Capabilities: %d",
                              (spt_agree_data & 0x0f));
          spt_offset += 1;

          spt_edge_count = tvb_get_ntohs(tvb, spt_offset);

          proto_tree_add_text(agreement_tree, tvb, spt_offset, 2,
                              "Agreement Digest Edge Count: %d", spt_edge_count);
          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);
    }
  }
}

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_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 }},
	{ &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 } },
  };
  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 }}
  };

  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));

  register_dissector("bpdu", dissect_bpdu_generic, proto_bpdu);
  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)
{
  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");

  bpdu_handle = find_dissector("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", 0x010c, bpdu_handle); /* Cisco's VLAN-bridge STP is just plain STP */

  bpdu_handle = find_dissector("bpdu_cisco");
  dissector_add_uint("llc.cisco_pid", 0x010b, bpdu_handle); /* Handle Cisco's (R)PVST+ TLV extensions */
}
