3 * The Regents of the University of California. All rights reserved.
5 * Redistribution and use in source and binary forms are permitted
6 * provided that the above copyright notice and this paragraph are
7 * duplicated in all such forms and that any documentation,
8 * advertising materials, and other materials related to such
9 * distribution and use acknowledge that the software was developed
10 * by the University of California, Lawrence Berkeley Laboratory,
11 * Berkeley, CA. The name of the University may not be used to
12 * endorse or promote products derived from this software without
13 * specific prior written permission.
14 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
15 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
16 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
18 * Initial contribution from John Hawkinson <jhawk@bbnplanet.com>
20 * This module implements support for decoding GRE (Generic Routing
21 * Encapsulation) tunnels; they're documented in RFC1701 and RFC1702.
22 * This code only supports the IP encapsulation thereof.
26 static const char rcsid[] =
27 "@(#) $Header: /tcpdump/master/tcpdump/print-gre.c,v 1.13 2001/06/15 22:17:31 fenner Exp $";
34 #include <sys/param.h>
37 #include <sys/socket.h>
39 #include <netinet/in.h>
44 #include "interface.h"
45 #include "addrtoname.h"
46 #include "extract.h" /* must come after interface.h */
54 #define GRE_CP 0x8000 /* Checksum Present */
55 #define GRE_VER_MASK 0x0007 /* Version */
57 /* RFC 2890 - Key and Sequence extensions to GRE */
58 #define GRE_KP 0x2000 /* Key Present */
59 #define GRE_SP 0x1000 /* Sequence Present */
61 /* Legacy from RFC 1700 */
62 #define GRE_RP 0x4000 /* Routing Present */
63 #define GRE_sP 0x0800 /* strict source route present */
64 #define GRE_RECUR_MASK 0x0700 /* Recursion Control */
65 #define GRE_RECUR_SHIFT 8
67 #define GRE_COP (GRE_RP|GRE_CP) /* Checksum & Offset Present */
69 /* "Enhanced GRE" from RFC2637 - PPTP */
70 #define GRE_AP 0x0080 /* Ack present */
72 #define GRE_MBZ_MASK 0x0078 /* not defined */
75 * Deencapsulate and print a GRE-tunneled IP datagram
78 gre_print(const u_char *bp, u_int length)
80 const u_char *cp = bp + 4;
81 const struct gre *gre;
82 u_int16_t flags, proto;
84 u_short extracted_ethertype;
86 gre = (const struct gre *)bp;
89 flags = EXTRACT_16BITS(&gre->flags);
90 proto = EXTRACT_16BITS(&gre->proto);
94 /* Decode the flags */
108 if (flags & GRE_RECUR_MASK)
109 printf("R%x", (flags & GRE_RECUR_MASK) >> GRE_RECUR_SHIFT);
110 ver = flags & GRE_VER_MASK;
113 if (flags & GRE_MBZ_MASK)
114 printf("!%x", flags & GRE_MBZ_MASK);
118 if (flags & GRE_COP) {
119 int checksum, offset;
122 checksum = EXTRACT_16BITS(cp);
123 offset = EXTRACT_16BITS(cp + 2);
125 if (flags & GRE_CP) {
126 /* Checksum present */
128 /* todo: check checksum */
130 printf("C:%04x ", checksum);
132 if (flags & GRE_RP) {
136 printf("O:%04x ", offset);
138 cp += 4; /* skip checksum and offset */
140 if (flags & GRE_KP) {
142 if (ver == 1) { /* PPTP */
144 printf("PL:%u ", EXTRACT_16BITS(cp));
145 printf("ID:%04x ", EXTRACT_16BITS(cp+2));
148 printf("K:%08x ", EXTRACT_32BITS(cp));
149 cp += 4; /* skip key */
151 if (flags & GRE_SP) {
153 printf("S:%u ", EXTRACT_32BITS(cp));
154 cp += 4; /* skip seq */
156 if (flags & GRE_AP && ver >= 1) {
158 printf("A:%u ", EXTRACT_32BITS(cp));
159 cp += 4; /* skip ack */
161 /* We don't support routing fields (variable length) now. Punt. */
168 if (ether_encap_print(proto, cp, length, length,
169 &extracted_ethertype) == 0)
170 printf("gre-proto-0x%04X", proto);
174 fputs("[|gre]", stdout);