2 * Routines for null packet disassembly
4 * $Id: packet-null.c,v 1.24 2000/05/25 07:42:24 gram Exp $
6 * Ethereal - Network traffic analyzer
7 * By Gerald Combs <gerald@zing.org>
9 * This file created and by Mike Hall <mlh@io.com>
12 * This program is free software; you can redistribute it and/or
13 * modify it under the terms of the GNU General Public License
14 * as published by the Free Software Foundation; either version 2
15 * of the License, or (at your option) any later version.
17 * This program is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU General Public License for more details.
22 * You should have received a copy of the GNU General Public License
23 * along with this program; if not, write to the Free Software
24 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
31 #ifdef HAVE_SYS_TYPES_H
32 #include <sys/types.h>
37 #ifdef HAVE_SYS_SOCKET_H
38 #include <sys/socket.h>
42 #include "packet-null.h"
43 #include "packet-atalk.h"
44 #include "packet-ip.h"
45 #include "packet-ipv6.h"
46 #include "packet-ipx.h"
47 #include "packet-osi.h"
48 #include "packet-ppp.h"
51 extern const value_string etype_vals[];
53 /* protocols and header fields */
54 static int proto_null = -1;
55 static int hf_null_etype = -1;
56 static int hf_null_family = -1;
58 static gint ett_null = -1;
60 /* Null/loopback structs and definitions */
62 /* Macro to byte-swap 32-bit quantities. */
64 ((((x)&0xFF000000)>>24) | \
65 (((x)&0x00FF0000)>>8) | \
66 (((x)&0x0000FF00)<<8) | \
67 (((x)&0x000000FF)<<24))
72 #define BSD_AF_APPLETALK 16
74 #define BSD_AF_INET6_BSD 24 /* OpenBSD (and probably NetBSD), BSD/OS */
75 #define BSD_AF_INET6_FREEBSD 28
78 static const value_string family_vals[] = {
81 {BSD_AF_APPLETALK, "Appletalk" },
82 {BSD_AF_IPX, "Netware IPX/SPX"},
83 {BSD_AF_INET6_BSD, "IPv6" },
84 {BSD_AF_INET6_FREEBSD, "IPv6" },
89 capture_null( const u_char *pd, packet_counts *ld )
94 * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD
95 * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers -
96 * appear to stuff the AF_ value for the protocol, in *host* byte
97 * order, in the first four bytes.
99 * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that
100 * Andreas Klemm sent to ethereal-dev has a packet type of DLT_NULL,
101 * and the family bits look like PPP's protocol field. (Was this an
102 * older, or different, ISDN driver?) Looking at what appears to be
103 * that capture file, it appears that it's using PPP in HDLC framing,
104 * RFC 1549, wherein the first two octets of the frame are 0xFF
105 * (address) and 0x03 (control), so the header bytes are, in order:
109 * high-order byte of a PPP protocol field
110 * low-order byte of a PPP protocol field
112 * when reading it on a little-endian machine; that means it's
113 * PPPP03FF, where PPPP is a byte-swapped PPP protocol field.
115 * "libpcap" for Linux uses DLT_NULL only for the loopback device.
116 * The loopback driver in Linux 2.0.36, at least, puts an *Ethernet*
117 * header at the beginning of loopback packets; however, "libpcap"
118 * for Linux compensates for this by skipping the source and
119 * destination MAC addresses, replacing them with 2 bytes of 0.
120 * This means that if we're reading the capture on a little-endian
121 * machine, the header, treated as a 32-bit integer, looks like
123 * EEEEEEEEEEEEEEEE0000000000000000
125 * where "EEEEEEEEEEEEEEEE" is the Ethernet type, and if we're reading
126 * it on a big-endian machine, it looks like
128 * 0000000000000000EEEEEEEEEEEEEEEE
130 * The Ethernet type might or might not be byte-swapped; I haven't
131 * bothered thinking about that yet.
133 * AF_ values are (relatively) small integers, and shouldn't have their
134 * upper 16 bits zero; Ethernet types have to fit in 16 bits and
135 * thus must have their upper 16 bits zero. Therefore, if the upper
136 * 16 bits of the field aren't zero, it's in the wrong byte order.
138 * Ethernet types are bigger than 1536, and AF_ values are smaller
139 * than 1536, so we needn't worry about one being mistaken for
140 * the other. (There may be a problem if the 16-bit Ethernet
141 * type is byte-swapped as a 16-bit quantity, but if when treated
142 * as a 32-bit quantity its upper 16 bits are zero, but I'll think
143 * about that one later.)
145 * As for the PPP protocol field values:
147 * 0x0000 does not appear to be a valid PPP protocol field value,
148 * so the upper 16 bits will be non-zero, and we'll byte swap it.
153 * where PPPP is a non-byte-swapped PPP protocol field; we'll
154 * check for the upper 16 bits of the byte-swapped field being
155 * non-zero and, if so, assume the lower 16 bits are a PPP
156 * protocol field (AF_ and Ethernet protocol fields should leave
157 * the upper 16 bits zero - unless somebody stuff something else
160 * So, to compensate for this mess, we:
162 * check if the first two octets are 0xFF and 0x03 and, if so,
163 * treat it as a PPP frame;
165 * otherwise, byte-swap the value if its upper 16 bits aren't zero,
166 * and compare the lower 16 bits of the value against Ethernet
169 * If, as implied by an earlier version of the "e_nullhdr" structure,
170 * the family is only 16 bits, and there are "next" and "len" fields
171 * before it, that all goes completely to hell. (Note that, for
172 * the BSD header, we could byte-swap it if the capture was written
173 * on a machine with the opposite byte-order to ours - the "libpcap"
174 * header lets us determine that - but it's more of a mess for Linux,
175 * given that the effect of inserting the two 0 bytes depends only
176 * on the byte order of the machine reading the file.)
178 if (pd[0] == 0xFF && pd[1] == 0x03) {
182 capture_ppp(pd, 0, ld);
185 * Treat it as a normal DLT_NULL header.
187 memcpy((char *)&null_header, (char *)&pd[0], sizeof(null_header));
189 if ((null_header & 0xFFFF0000) != 0) {
191 null_header = BSWAP32(null_header);
195 * The null header value must be greater than the IEEE 802.3 maximum
196 * frame length to be a valid Ethernet type; if it is, hand it
197 * to "ethertype()", otherwise treat it as a BSD AF_type (we wire
198 * in the values of the BSD AF_ types, because the values
199 * in the file will be BSD values, and the OS on which
200 * we're building this might not have the same values or
201 * might not have them defined at all; XXX - what if different
202 * BSD derivatives have different values?).
204 if (null_header > IEEE_802_3_MAX_LEN)
205 capture_ethertype(null_header, 4, pd, ld);
207 switch (null_header) {
210 capture_ip(pd, 4, ld);
222 dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
228 const guint8 *next_pd;
232 * See comment in "capture_null()" for an explanation of what we're
235 if (tvb_get_ntohs(tvb, 0) == 0xFF03) {
239 dissect_ppp(tvb, pinfo, tree);
242 /* load the top pane info. This should be overwritten by
243 the next protocol in the stack */
244 if(check_col(pinfo->fd, COL_RES_DL_SRC))
245 col_add_str(pinfo->fd, COL_RES_DL_SRC, "N/A" );
246 if(check_col(pinfo->fd, COL_RES_DL_DST))
247 col_add_str(pinfo->fd, COL_RES_DL_DST, "N/A" );
248 if(check_col(pinfo->fd, COL_PROTOCOL))
249 col_add_str(pinfo->fd, COL_PROTOCOL, "N/A" );
250 if(check_col(pinfo->fd, COL_INFO))
251 col_add_str(pinfo->fd, COL_INFO, "Null/Loopback" );
254 * Treat it as a normal DLT_NULL header.
256 memcpy((char *)&null_header, (char *)tvb_get_ptr(tvb, 0, sizeof(null_header)), sizeof(null_header));
258 if ((null_header & 0xFFFF0000) != 0) {
260 null_header = BSWAP32(null_header);
264 * The null header value must be greater than the IEEE 802.3 maximum
265 * frame length to be a valid Ethernet type; if it is, hand it
266 * to "ethertype()", otherwise treat it as a BSD AF_type (we wire
267 * in the values of the BSD AF_ types, because the values
268 * in the file will be BSD values, and the OS on which
269 * we're building this might not have the same values or
270 * might not have them defined at all; XXX - what if different
271 * BSD derivatives have different values?).
273 if (null_header > IEEE_802_3_MAX_LEN) {
275 ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, NULL);
276 fh_tree = proto_item_add_subtree(ti, ett_null);
279 ethertype(null_header, tvb, 4, pinfo, tree, fh_tree, hf_null_etype);
281 /* populate a tree in the second pane with the status of the link
284 ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, NULL);
285 fh_tree = proto_item_add_subtree(ti, ett_null);
286 proto_tree_add_item(fh_tree, hf_null_family, tvb, 0, 4, null_header);
289 next_tvb = tvb_new_subset(tvb, 4, -1, -1);
290 tvb_compat(next_tvb, &next_pd, &next_offset);
292 switch (null_header) {
295 dissect_ip(next_pd, next_offset, pinfo->fd, tree);
298 case BSD_AF_APPLETALK:
299 dissect_ddp(next_pd, next_offset, pinfo->fd, tree);
303 dissect_ipx(next_pd, next_offset, pinfo->fd, tree);
307 dissect_osi(next_pd, next_offset, pinfo->fd, tree);
310 case BSD_AF_INET6_BSD:
311 case BSD_AF_INET6_FREEBSD:
312 dissect_ipv6(next_pd, next_offset, pinfo->fd, tree);
316 dissect_data_tvb(next_tvb, pinfo, tree);
324 proto_register_null(void)
326 static hf_register_info hf[] = {
328 /* registered here but handled in ethertype.c */
330 { "Type", "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0,
334 { "Family", "null.family", FT_UINT32, BASE_HEX, VALS(family_vals), 0x0,
337 static gint *ett[] = {
341 proto_null = proto_register_protocol ("Null/Loopback", "null" );
342 proto_register_field_array(proto_null, hf, array_length(hf));
343 proto_register_subtree_array(ett, array_length(ett));