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1 /*
2  * Copyright (c) 2000 Lennert Buytenhek
3  *
4  * This software may be distributed either under the terms of the
5  * BSD-style license that accompanies tcpdump or the GNU General
6  * Public License
7  *
8  * Contributed by Lennert Buytenhek <buytenh@gnu.org>
9  */
10 
11 /* \summary: IEEE 802.1d Spanning Tree Protocol (STP) printer */
12 
13 #ifdef HAVE_CONFIG_H
14 #include "config.h"
15 #endif
16 
17 #include <netdissect-stdinc.h>
18 
19 #include <stdio.h>
20 
21 #include "netdissect.h"
22 #include "extract.h"
23 
24 #define	RSTP_EXTRACT_PORT_ROLE(x) (((x)&0x0C)>>2)
25 /* STP timers are expressed in multiples of 1/256th second */
26 #define STP_TIME_BASE 256
27 #define STP_BPDU_MSTP_MIN_LEN 102
28 
29 struct stp_bpdu_ {
30     uint8_t protocol_id[2];
31     uint8_t protocol_version;
32     uint8_t bpdu_type;
33     uint8_t flags;
34     uint8_t root_id[8];
35     uint8_t root_path_cost[4];
36     uint8_t bridge_id[8];
37     uint8_t port_id[2];
38     uint8_t message_age[2];
39     uint8_t max_age[2];
40     uint8_t hello_time[2];
41     uint8_t forward_delay[2];
42     uint8_t v1_length;
43 };
44 
45 #define STP_PROTO_REGULAR 0x00
46 #define STP_PROTO_RAPID   0x02
47 #define STP_PROTO_MSTP    0x03
48 #define STP_PROTO_SPB     0x04
49 
50 static const struct tok stp_proto_values[] = {
51     { STP_PROTO_REGULAR, "802.1d" },
52     { STP_PROTO_RAPID, "802.1w" },
53     { STP_PROTO_MSTP, "802.1s" },
54     { STP_PROTO_SPB, "802.1aq" },
55     { 0, NULL}
56 };
57 
58 #define STP_BPDU_TYPE_CONFIG      0x00
59 #define STP_BPDU_TYPE_RSTP        0x02
60 #define STP_BPDU_TYPE_TOPO_CHANGE 0x80
61 
62 static const struct tok stp_bpdu_flag_values[] = {
63     { 0x01, "Topology change" },
64     { 0x02, "Proposal" },
65     { 0x10, "Learn" },
66     { 0x20, "Forward" },
67     { 0x40, "Agreement" },
68     { 0x80, "Topology change ACK" },
69     { 0, NULL}
70 };
71 
72 static const struct tok stp_bpdu_type_values[] = {
73     { STP_BPDU_TYPE_CONFIG, "Config" },
74     { STP_BPDU_TYPE_RSTP, "Rapid STP" },
75     { STP_BPDU_TYPE_TOPO_CHANGE, "Topology Change" },
76     { 0, NULL}
77 };
78 
79 static const struct tok rstp_obj_port_role_values[] = {
80     { 0x00, "Unknown" },
81     { 0x01, "Alternate" },
82     { 0x02, "Root" },
83     { 0x03, "Designated" },
84     { 0, NULL}
85 };
86 
87 #define ND_TCHECK_BRIDGE_ID(p) ND_TCHECK2(*(p), 8)
88 
89 static char *
stp_print_bridge_id(const u_char * p)90 stp_print_bridge_id(const u_char *p)
91 {
92     static char bridge_id_str[sizeof("pppp.aa:bb:cc:dd:ee:ff")];
93 
94     snprintf(bridge_id_str, sizeof(bridge_id_str),
95              "%.2x%.2x.%.2x:%.2x:%.2x:%.2x:%.2x:%.2x",
96              p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7]);
97 
98     return bridge_id_str;
99 }
100 
101 static int
stp_print_config_bpdu(netdissect_options * ndo,const struct stp_bpdu_ * stp_bpdu,u_int length)102 stp_print_config_bpdu(netdissect_options *ndo, const struct stp_bpdu_ *stp_bpdu,
103                       u_int length)
104 {
105     ND_TCHECK(stp_bpdu->flags);
106     ND_PRINT((ndo, ", Flags [%s]",
107            bittok2str(stp_bpdu_flag_values, "none", stp_bpdu->flags)));
108 
109     ND_TCHECK(stp_bpdu->port_id);
110     ND_PRINT((ndo, ", bridge-id %s.%04x, length %u",
111            stp_print_bridge_id((const u_char *)&stp_bpdu->bridge_id),
112            EXTRACT_16BITS(&stp_bpdu->port_id), length));
113 
114     /* in non-verbose mode just print the bridge-id */
115     if (!ndo->ndo_vflag) {
116         return 1;
117     }
118 
119     ND_TCHECK(stp_bpdu->forward_delay);
120     ND_PRINT((ndo, "\n\tmessage-age %.2fs, max-age %.2fs"
121            ", hello-time %.2fs, forwarding-delay %.2fs",
122            (float)EXTRACT_16BITS(&stp_bpdu->message_age) / STP_TIME_BASE,
123            (float)EXTRACT_16BITS(&stp_bpdu->max_age) / STP_TIME_BASE,
124            (float)EXTRACT_16BITS(&stp_bpdu->hello_time) / STP_TIME_BASE,
125            (float)EXTRACT_16BITS(&stp_bpdu->forward_delay) / STP_TIME_BASE));
126 
127     ND_PRINT((ndo, "\n\troot-id %s, root-pathcost %u",
128            stp_print_bridge_id((const u_char *)&stp_bpdu->root_id),
129            EXTRACT_32BITS(&stp_bpdu->root_path_cost)));
130 
131     /* Port role is only valid for 802.1w */
132     if (stp_bpdu->protocol_version == STP_PROTO_RAPID) {
133         ND_PRINT((ndo, ", port-role %s",
134                tok2str(rstp_obj_port_role_values, "Unknown",
135                        RSTP_EXTRACT_PORT_ROLE(stp_bpdu->flags))));
136     }
137     return 1;
138 
139 trunc:
140     return 0;
141 }
142 
143 /*
144  * MSTP packet format
145  * Ref. IEEE 802.1Q 2003 Ed. Section 14
146  *
147  * MSTP BPDU
148  *
149  * 2 -  bytes Protocol Id
150  * 1 -  byte  Protocol Ver.
151  * 1 -  byte  BPDU tye
152  * 1 -  byte  Flags
153  * 8 -  bytes CIST Root Identifier
154  * 4 -  bytes CIST External Path Cost
155  * 8 -  bytes CIST Regional Root Identifier
156  * 2 -  bytes CIST Port Identifier
157  * 2 -  bytes Message Age
158  * 2 -  bytes Max age
159  * 2 -  bytes Hello Time
160  * 2 -  bytes Forward delay
161  * 1 -  byte  Version 1 length. Must be 0
162  * 2 -  bytes Version 3 length
163  * 1 -  byte  Config Identifier
164  * 32 - bytes Config Name
165  * 2 -  bytes Revision level
166  * 16 - bytes Config Digest [MD5]
167  * 4 -  bytes CIST Internal Root Path Cost
168  * 8 -  bytes CIST Bridge Identifier
169  * 1 -  byte  CIST Remaining Hops
170  * 16 - bytes MSTI information [Max 64 MSTI, each 16 bytes]
171  *
172  *
173  * SPB BPDU
174  * Ref. IEEE 802.1aq. Section 14
175  *
176  * 2 -  bytes Version 4 length
177  * 1 -  byte  Aux Config Identifier
178  * 32 - bytes Aux Config Name
179  * 2 -  bytes Aux Revision level
180  * 16 - bytes Aux Config Digest [MD5]
181  * 1 -  byte  (1 - 2) Agreement Number
182  *            (3 - 4) Discarded Agreement Number
183  *            (5) Agreement Valid Flag
184  *            (6) Restricted Role Flag
185  *            (7 - 8) Unused sent zero
186  * 1 -  byte Unused
187  * 1 -  byte (1 - 4) Agreement Digest Format Identifier
188  *           (5 - 8) Agreement Digest Format Capabilities
189  * 1 -  byte (1 - 4) Agreement Digest Convention Identifier
190  *           (5 - 8) Agreement Digest Convention Capabilities
191  * 2 -  bytes Agreement Digest Edge Count
192  * 8 -  byte Reserved Set
193  * 20 - bytes Computed Topology Digest
194  *
195  *
196  * MSTI Payload
197  *
198  * 1 - byte  MSTI flag
199  * 8 - bytes MSTI Regional Root Identifier
200  * 4 - bytes MSTI Regional Path Cost
201  * 1 - byte  MSTI Bridge Priority
202  * 1 - byte  MSTI Port Priority
203  * 1 - byte  MSTI Remaining Hops
204  *
205  */
206 
207 #define MST_BPDU_MSTI_LENGTH		    16
208 #define MST_BPDU_CONFIG_INFO_LENGTH	    64
209 
210 /* Offsets of fields from the begginning for the packet */
211 #define MST_BPDU_VER3_LEN_OFFSET	    36
212 #define MST_BPDU_CONFIG_NAME_OFFSET	    39
213 #define MST_BPDU_CONFIG_DIGEST_OFFSET	    73
214 #define MST_BPDU_CIST_INT_PATH_COST_OFFSET  89
215 #define MST_BPDU_CIST_BRIDGE_ID_OFFSET	    93
216 #define MST_BPDU_CIST_REMAIN_HOPS_OFFSET    101
217 #define MST_BPDU_MSTI_OFFSET		    102
218 /* Offsets within  an MSTI */
219 #define MST_BPDU_MSTI_ROOT_PRIO_OFFSET	    1
220 #define MST_BPDU_MSTI_ROOT_PATH_COST_OFFSET 9
221 #define MST_BPDU_MSTI_BRIDGE_PRIO_OFFSET    13
222 #define MST_BPDU_MSTI_PORT_PRIO_OFFSET	    14
223 #define MST_BPDU_MSTI_REMAIN_HOPS_OFFSET    15
224 
225 #define SPB_BPDU_MIN_LEN                  87
226 #define SPB_BPDU_CONFIG_NAME_OFFSET       3
227 #define SPB_BPDU_CONFIG_REV_OFFSET        SPB_BPDU_CONFIG_NAME_OFFSET + 32
228 #define SPB_BPDU_CONFIG_DIGEST_OFFSET     SPB_BPDU_CONFIG_REV_OFFSET + 2
229 #define SPB_BPDU_AGREEMENT_OFFSET         SPB_BPDU_CONFIG_DIGEST_OFFSET + 16
230 #define SPB_BPDU_AGREEMENT_UNUSED_OFFSET  SPB_BPDU_AGREEMENT_OFFSET + 1
231 #define SPB_BPDU_AGREEMENT_FORMAT_OFFSET  SPB_BPDU_AGREEMENT_UNUSED_OFFSET + 1
232 #define SPB_BPDU_AGREEMENT_CON_OFFSET     SPB_BPDU_AGREEMENT_FORMAT_OFFSET + 1
233 #define SPB_BPDU_AGREEMENT_EDGE_OFFSET    SPB_BPDU_AGREEMENT_CON_OFFSET + 1
234 #define SPB_BPDU_AGREEMENT_RES1_OFFSET    SPB_BPDU_AGREEMENT_EDGE_OFFSET + 2
235 #define SPB_BPDU_AGREEMENT_RES2_OFFSET    SPB_BPDU_AGREEMENT_RES1_OFFSET + 4
236 #define SPB_BPDU_AGREEMENT_DIGEST_OFFSET  SPB_BPDU_AGREEMENT_RES2_OFFSET + 4
237 
238 static int
stp_print_mstp_bpdu(netdissect_options * ndo,const struct stp_bpdu_ * stp_bpdu,u_int length)239 stp_print_mstp_bpdu(netdissect_options *ndo, const struct stp_bpdu_ *stp_bpdu,
240                     u_int length)
241 {
242     const u_char *ptr;
243     uint16_t	    v3len;
244     uint16_t	    len;
245     uint16_t	    msti;
246     u_int	    offset;
247 
248     ptr = (const u_char *)stp_bpdu;
249     ND_PRINT((ndo, ", CIST Flags [%s], length %u",
250            bittok2str(stp_bpdu_flag_values, "none", stp_bpdu->flags), length));
251 
252     /*
253      * in non-verbose mode just print the flags.
254      */
255     if (!ndo->ndo_vflag) {
256         return 1;
257     }
258 
259     ND_PRINT((ndo, "\n\tport-role %s, ",
260            tok2str(rstp_obj_port_role_values, "Unknown",
261                    RSTP_EXTRACT_PORT_ROLE(stp_bpdu->flags))));
262 
263     ND_TCHECK(stp_bpdu->root_path_cost);
264     ND_PRINT((ndo, "CIST root-id %s, CIST ext-pathcost %u",
265            stp_print_bridge_id((const u_char *)&stp_bpdu->root_id),
266            EXTRACT_32BITS(&stp_bpdu->root_path_cost)));
267 
268     ND_TCHECK(stp_bpdu->bridge_id);
269     ND_PRINT((ndo, "\n\tCIST regional-root-id %s, ",
270            stp_print_bridge_id((const u_char *)&stp_bpdu->bridge_id)));
271 
272     ND_TCHECK(stp_bpdu->port_id);
273     ND_PRINT((ndo, "CIST port-id %04x,", EXTRACT_16BITS(&stp_bpdu->port_id)));
274 
275     ND_TCHECK(stp_bpdu->forward_delay);
276     ND_PRINT((ndo, "\n\tmessage-age %.2fs, max-age %.2fs"
277            ", hello-time %.2fs, forwarding-delay %.2fs",
278            (float)EXTRACT_16BITS(&stp_bpdu->message_age) / STP_TIME_BASE,
279            (float)EXTRACT_16BITS(&stp_bpdu->max_age) / STP_TIME_BASE,
280            (float)EXTRACT_16BITS(&stp_bpdu->hello_time) / STP_TIME_BASE,
281            (float)EXTRACT_16BITS(&stp_bpdu->forward_delay) / STP_TIME_BASE));
282 
283     ND_TCHECK_16BITS(ptr + MST_BPDU_VER3_LEN_OFFSET);
284     ND_PRINT((ndo, "\n\tv3len %d, ", EXTRACT_16BITS(ptr + MST_BPDU_VER3_LEN_OFFSET)));
285     ND_TCHECK_32BITS(ptr + MST_BPDU_CONFIG_DIGEST_OFFSET + 12);
286     ND_PRINT((ndo, "MCID Name "));
287     if (fn_printzp(ndo, ptr + MST_BPDU_CONFIG_NAME_OFFSET, 32, ndo->ndo_snapend))
288 	goto trunc;
289     ND_PRINT((ndo, ", rev %u,"
290             "\n\t\tdigest %08x%08x%08x%08x, ",
291 	          EXTRACT_16BITS(ptr + MST_BPDU_CONFIG_NAME_OFFSET + 32),
292 	          EXTRACT_32BITS(ptr + MST_BPDU_CONFIG_DIGEST_OFFSET),
293 	          EXTRACT_32BITS(ptr + MST_BPDU_CONFIG_DIGEST_OFFSET + 4),
294 	          EXTRACT_32BITS(ptr + MST_BPDU_CONFIG_DIGEST_OFFSET + 8),
295 	          EXTRACT_32BITS(ptr + MST_BPDU_CONFIG_DIGEST_OFFSET + 12)));
296 
297     ND_TCHECK_32BITS(ptr + MST_BPDU_CIST_INT_PATH_COST_OFFSET);
298     ND_PRINT((ndo, "CIST int-root-pathcost %u,",
299             EXTRACT_32BITS(ptr + MST_BPDU_CIST_INT_PATH_COST_OFFSET)));
300 
301     ND_TCHECK_BRIDGE_ID(ptr + MST_BPDU_CIST_BRIDGE_ID_OFFSET);
302     ND_PRINT((ndo, "\n\tCIST bridge-id %s, ",
303            stp_print_bridge_id(ptr + MST_BPDU_CIST_BRIDGE_ID_OFFSET)));
304 
305     ND_TCHECK(ptr[MST_BPDU_CIST_REMAIN_HOPS_OFFSET]);
306     ND_PRINT((ndo, "CIST remaining-hops %d", ptr[MST_BPDU_CIST_REMAIN_HOPS_OFFSET]));
307 
308     /* Dump all MSTI's */
309     ND_TCHECK_16BITS(ptr + MST_BPDU_VER3_LEN_OFFSET);
310     v3len = EXTRACT_16BITS(ptr + MST_BPDU_VER3_LEN_OFFSET);
311     if (v3len > MST_BPDU_CONFIG_INFO_LENGTH) {
312         len = v3len - MST_BPDU_CONFIG_INFO_LENGTH;
313         offset = MST_BPDU_MSTI_OFFSET;
314         while (len >= MST_BPDU_MSTI_LENGTH) {
315             ND_TCHECK2(*(ptr + offset), MST_BPDU_MSTI_LENGTH);
316 
317             msti = EXTRACT_16BITS(ptr + offset +
318                                   MST_BPDU_MSTI_ROOT_PRIO_OFFSET);
319             msti = msti & 0x0FFF;
320 
321             ND_PRINT((ndo, "\n\tMSTI %d, Flags [%s], port-role %s",
322                    msti, bittok2str(stp_bpdu_flag_values, "none", ptr[offset]),
323                    tok2str(rstp_obj_port_role_values, "Unknown",
324                            RSTP_EXTRACT_PORT_ROLE(ptr[offset]))));
325             ND_PRINT((ndo, "\n\t\tMSTI regional-root-id %s, pathcost %u",
326                    stp_print_bridge_id(ptr + offset +
327                                        MST_BPDU_MSTI_ROOT_PRIO_OFFSET),
328                    EXTRACT_32BITS(ptr + offset +
329                                   MST_BPDU_MSTI_ROOT_PATH_COST_OFFSET)));
330             ND_PRINT((ndo, "\n\t\tMSTI bridge-prio %d, port-prio %d, hops %d",
331                    ptr[offset + MST_BPDU_MSTI_BRIDGE_PRIO_OFFSET] >> 4,
332                    ptr[offset + MST_BPDU_MSTI_PORT_PRIO_OFFSET] >> 4,
333                    ptr[offset + MST_BPDU_MSTI_REMAIN_HOPS_OFFSET]));
334 
335             len -= MST_BPDU_MSTI_LENGTH;
336             offset += MST_BPDU_MSTI_LENGTH;
337         }
338     }
339     return 1;
340 
341 trunc:
342     return 0;
343 }
344 
345 static int
stp_print_spb_bpdu(netdissect_options * ndo,const struct stp_bpdu_ * stp_bpdu,u_int offset)346 stp_print_spb_bpdu(netdissect_options *ndo, const struct stp_bpdu_ *stp_bpdu,
347                    u_int offset)
348 {
349     const u_char *ptr;
350 
351     /*
352      * in non-verbose mode don't print anything.
353      */
354     if (!ndo->ndo_vflag) {
355         return 1;
356     }
357 
358     ptr = (const u_char *)stp_bpdu;
359     ND_TCHECK_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET + 16);
360 
361     ND_PRINT((ndo, "\n\tv4len %d, ", EXTRACT_16BITS (ptr + offset)));
362     ND_PRINT((ndo, "AUXMCID Name "));
363     if (fn_printzp(ndo, ptr + offset + SPB_BPDU_CONFIG_NAME_OFFSET, 32,
364 		   ndo->ndo_snapend))
365 	goto trunc;
366     ND_PRINT((ndo, ", Rev %u,\n\t\tdigest %08x%08x%08x%08x",
367             EXTRACT_16BITS(ptr + offset + SPB_BPDU_CONFIG_REV_OFFSET),
368             EXTRACT_32BITS(ptr + offset + SPB_BPDU_CONFIG_DIGEST_OFFSET),
369             EXTRACT_32BITS(ptr + offset + SPB_BPDU_CONFIG_DIGEST_OFFSET + 4),
370             EXTRACT_32BITS(ptr + offset + SPB_BPDU_CONFIG_DIGEST_OFFSET + 8),
371             EXTRACT_32BITS(ptr + offset + SPB_BPDU_CONFIG_DIGEST_OFFSET + 12)));
372 
373     ND_PRINT((ndo, "\n\tAgreement num %d, Discarded Agreement num %d, Agreement valid-"
374             "flag %d,\n\tRestricted role-flag: %d, Format id %d cap %d, "
375             "Convention id %d cap %d,\n\tEdge count %d, "
376             "Agreement digest %08x%08x%08x%08x%08x\n",
377             ptr[offset + SPB_BPDU_AGREEMENT_OFFSET]>>6,
378             ptr[offset + SPB_BPDU_AGREEMENT_OFFSET]>>4 & 0x3,
379             ptr[offset + SPB_BPDU_AGREEMENT_OFFSET]>>3 & 0x1,
380             ptr[offset + SPB_BPDU_AGREEMENT_OFFSET]>>2 & 0x1,
381             ptr[offset + SPB_BPDU_AGREEMENT_FORMAT_OFFSET]>>4,
382             ptr[offset + SPB_BPDU_AGREEMENT_FORMAT_OFFSET]&0x00ff,
383             ptr[offset + SPB_BPDU_AGREEMENT_CON_OFFSET]>>4,
384             ptr[offset + SPB_BPDU_AGREEMENT_CON_OFFSET]&0x00ff,
385             EXTRACT_16BITS(ptr + offset + SPB_BPDU_AGREEMENT_EDGE_OFFSET),
386             EXTRACT_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET),
387             EXTRACT_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET+4),
388             EXTRACT_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET+8),
389             EXTRACT_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET+12),
390             EXTRACT_32BITS(ptr + offset + SPB_BPDU_AGREEMENT_DIGEST_OFFSET+16)));
391     return 1;
392 
393 trunc:
394     return 0;
395 }
396 
397 /*
398  * Print 802.1d / 802.1w / 802.1q (mstp) / 802.1aq (spb) packets.
399  */
400 void
stp_print(netdissect_options * ndo,const u_char * p,u_int length)401 stp_print(netdissect_options *ndo, const u_char *p, u_int length)
402 {
403     const struct stp_bpdu_ *stp_bpdu;
404     u_int                  mstp_len;
405     u_int                  spb_len;
406 
407     stp_bpdu = (const struct stp_bpdu_*)p;
408 
409     /* Minimum STP Frame size. */
410     if (length < 4)
411         goto trunc;
412 
413     ND_TCHECK(stp_bpdu->protocol_id);
414     if (EXTRACT_16BITS(&stp_bpdu->protocol_id)) {
415         ND_PRINT((ndo, "unknown STP version, length %u", length));
416         return;
417     }
418 
419     ND_TCHECK(stp_bpdu->protocol_version);
420     ND_PRINT((ndo, "STP %s", tok2str(stp_proto_values, "Unknown STP protocol (0x%02x)",
421                          stp_bpdu->protocol_version)));
422 
423     switch (stp_bpdu->protocol_version) {
424     case STP_PROTO_REGULAR:
425     case STP_PROTO_RAPID:
426     case STP_PROTO_MSTP:
427     case STP_PROTO_SPB:
428         break;
429     default:
430         return;
431     }
432 
433     ND_TCHECK(stp_bpdu->bpdu_type);
434     ND_PRINT((ndo, ", %s", tok2str(stp_bpdu_type_values, "Unknown BPDU Type (0x%02x)",
435                            stp_bpdu->bpdu_type)));
436 
437     switch (stp_bpdu->bpdu_type) {
438     case STP_BPDU_TYPE_CONFIG:
439         if (length < sizeof(struct stp_bpdu_) - 1) {
440             goto trunc;
441         }
442         if (!stp_print_config_bpdu(ndo, stp_bpdu, length))
443             goto trunc;
444         break;
445 
446     case STP_BPDU_TYPE_RSTP:
447         if (stp_bpdu->protocol_version == STP_PROTO_RAPID) {
448             if (length < sizeof(struct stp_bpdu_)) {
449                 goto trunc;
450             }
451             if (!stp_print_config_bpdu(ndo, stp_bpdu, length))
452                 goto trunc;
453         } else if (stp_bpdu->protocol_version == STP_PROTO_MSTP ||
454                    stp_bpdu->protocol_version == STP_PROTO_SPB) {
455             if (length < STP_BPDU_MSTP_MIN_LEN) {
456                 goto trunc;
457             }
458 
459             ND_TCHECK(stp_bpdu->v1_length);
460             if (stp_bpdu->v1_length != 0) {
461                 /* FIX ME: Emit a message here ? */
462                 goto trunc;
463             }
464 
465             /* Validate v3 length */
466             ND_TCHECK_16BITS(p + MST_BPDU_VER3_LEN_OFFSET);
467             mstp_len = EXTRACT_16BITS(p + MST_BPDU_VER3_LEN_OFFSET);
468             mstp_len += 2;  /* length encoding itself is 2 bytes */
469             if (length < (sizeof(struct stp_bpdu_) + mstp_len)) {
470                 goto trunc;
471             }
472             if (!stp_print_mstp_bpdu(ndo, stp_bpdu, length))
473                 goto trunc;
474 
475             if (stp_bpdu->protocol_version == STP_PROTO_SPB)
476             {
477               /* Validate v4 length */
478               spb_len = EXTRACT_16BITS (p + MST_BPDU_VER3_LEN_OFFSET + mstp_len);
479               spb_len += 2;
480               if (length < (sizeof(struct stp_bpdu_) + mstp_len + spb_len) ||
481                   spb_len < SPB_BPDU_MIN_LEN) {
482                 goto trunc;
483               }
484               if (!stp_print_spb_bpdu(ndo, stp_bpdu, (sizeof(struct stp_bpdu_) + mstp_len)))
485                 goto trunc;
486             }
487         }
488         break;
489 
490     case STP_BPDU_TYPE_TOPO_CHANGE:
491         /* always empty message - just break out */
492         break;
493 
494     default:
495         break;
496     }
497 
498     return;
499 trunc:
500     ND_PRINT((ndo, "[|stp %d]", length));
501 }
502 
503 /*
504  * Local Variables:
505  * c-style: whitesmith
506  * c-basic-offset: 4
507  * End:
508  */
509