2 * Routines for null packet disassembly
4 * $Id: packet-null.c,v 1.44 2001/04/17 06:43:19 guy 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>
43 #include "packet-null.h"
44 #include "atalk-utils.h"
45 #include "packet-ip.h"
46 #include "packet-ipv6.h"
47 #include "packet-ipx.h"
48 #include "packet-osi.h"
49 #include "packet-ppp.h"
53 static dissector_table_t null_dissector_table;
55 /* protocols and header fields */
56 static int proto_null = -1;
57 static int hf_null_etype = -1;
58 static int hf_null_family = -1;
60 static gint ett_null = -1;
62 /* Null/loopback structs and definitions */
65 static const value_string family_vals[] = {
68 {BSD_AF_APPLETALK, "Appletalk" },
69 {BSD_AF_IPX, "Netware IPX/SPX"},
70 {BSD_AF_INET6_BSD, "IPv6" },
71 {BSD_AF_INET6_FREEBSD, "IPv6" },
75 static dissector_handle_t ppp_hdlc_handle;
78 capture_null( const u_char *pd, packet_counts *ld )
83 * BSD drivers that use DLT_NULL - including the FreeBSD 3.2 ISDN-for-BSD
84 * drivers, as well as the 4.4-Lite and FreeBSD loopback drivers -
85 * appear to stuff the AF_ value for the protocol, in *host* byte
86 * order, in the first four bytes.
88 * However, according to Gerald Combs, a FreeBSD ISDN PPP dump that
89 * Andreas Klemm sent to ethereal-dev has a packet type of DLT_NULL,
90 * and the family bits look like PPP's protocol field. (Was this an
91 * older, or different, ISDN driver?) Looking at what appears to be
92 * that capture file, it appears that it's using PPP in HDLC framing,
93 * RFC 1549, wherein the first two octets of the frame are 0xFF
94 * (address) and 0x03 (control), so the header bytes are, in order:
98 * high-order byte of a PPP protocol field
99 * low-order byte of a PPP protocol field
101 * when reading it on a little-endian machine; that means it's
102 * PPPP03FF, where PPPP is a byte-swapped PPP protocol field.
104 * "libpcap" for Linux uses DLT_NULL only for the loopback device.
105 * The loopback driver in Linux 2.0.36, at least, puts an *Ethernet*
106 * header at the beginning of loopback packets; however, "libpcap"
107 * for Linux compensates for this by skipping the source and
108 * destination MAC addresses, replacing them with 2 bytes of 0.
109 * This means that if we're reading the capture on a little-endian
110 * machine, the header, treated as a 32-bit integer, looks like
112 * EEEEEEEEEEEEEEEE0000000000000000
114 * where "EEEEEEEEEEEEEEEE" is the Ethernet type, and if we're reading
115 * it on a big-endian machine, it looks like
117 * 0000000000000000EEEEEEEEEEEEEEEE
119 * The Ethernet type might or might not be byte-swapped; I haven't
120 * bothered thinking about that yet.
122 * AF_ values are (relatively) small integers, and shouldn't have their
123 * upper 16 bits zero; Ethernet types have to fit in 16 bits and
124 * thus must have their upper 16 bits zero. Therefore, if the upper
125 * 16 bits of the field aren't zero, it's in the wrong byte order.
127 * Ethernet types are bigger than 1536, and AF_ values are smaller
128 * than 1536, so we needn't worry about one being mistaken for
129 * the other. (There may be a problem if the 16-bit Ethernet
130 * type is byte-swapped as a 16-bit quantity, but if when treated
131 * as a 32-bit quantity its upper 16 bits are zero, but I'll think
132 * about that one later.)
134 * As for the PPP protocol field values:
136 * 0x0000 does not appear to be a valid PPP protocol field value,
137 * so the upper 16 bits will be non-zero, and we'll byte swap it.
142 * where PPPP is a non-byte-swapped PPP protocol field; we'll
143 * check for the upper 16 bits of the byte-swapped field being
144 * non-zero and, if so, assume the lower 16 bits are a PPP
145 * protocol field (AF_ and Ethernet protocol fields should leave
146 * the upper 16 bits zero - unless somebody stuff something else
149 * So, to compensate for this mess, we:
151 * check if the first two octets are 0xFF and 0x03 and, if so,
152 * treat it as a PPP frame;
154 * otherwise, byte-swap the value if its upper 16 bits aren't zero,
155 * and compare the lower 16 bits of the value against Ethernet
158 * If, as implied by an earlier version of the "e_nullhdr" structure,
159 * the family is only 16 bits, and there are "next" and "len" fields
160 * before it, that all goes completely to hell. (Note that, for
161 * the BSD header, we could byte-swap it if the capture was written
162 * on a machine with the opposite byte-order to ours - the "libpcap"
163 * header lets us determine that - but it's more of a mess for Linux,
164 * given that the effect of inserting the two 0 bytes depends only
165 * on the byte order of the machine reading the file.)
167 if (pd[0] == 0xFF && pd[1] == 0x03) {
171 capture_ppp_hdlc(pd, 0, ld);
174 * Treat it as a normal DLT_NULL header.
176 memcpy((char *)&null_header, (char *)&pd[0], sizeof(null_header));
178 if ((null_header & 0xFFFF0000) != 0) {
180 null_header = BSWAP32(null_header);
184 * The null header value must be greater than the IEEE 802.3 maximum
185 * frame length to be a valid Ethernet type; if it is, hand it
186 * to "ethertype()", otherwise treat it as a BSD AF_type (we wire
187 * in the values of the BSD AF_ types, because the values
188 * in the file will be BSD values, and the OS on which
189 * we're building this might not have the same values or
190 * might not have them defined at all; XXX - what if different
191 * BSD derivatives have different values?).
193 if (null_header > IEEE_802_3_MAX_LEN)
194 capture_ethertype(null_header, 4, pd, ld);
196 switch (null_header) {
199 capture_ip(pd, 4, ld);
211 dissect_null(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
219 * See comment in "capture_null()" for an explanation of what we're
222 if (tvb_get_ntohs(tvb, 0) == 0xFF03) {
226 call_dissector(ppp_hdlc_handle, tvb, pinfo, tree);
229 /* load the top pane info. This should be overwritten by
230 the next protocol in the stack */
231 if(check_col(pinfo->fd, COL_RES_DL_SRC))
232 col_set_str(pinfo->fd, COL_RES_DL_SRC, "N/A" );
233 if(check_col(pinfo->fd, COL_RES_DL_DST))
234 col_set_str(pinfo->fd, COL_RES_DL_DST, "N/A" );
235 if(check_col(pinfo->fd, COL_PROTOCOL))
236 col_set_str(pinfo->fd, COL_PROTOCOL, "N/A" );
237 if(check_col(pinfo->fd, COL_INFO))
238 col_set_str(pinfo->fd, COL_INFO, "Null/Loopback" );
241 * Treat it as a normal DLT_NULL header.
243 tvb_memcpy(tvb, (guint8 *)&null_header, 0, sizeof(null_header));
245 if ((null_header & 0xFFFF0000) != 0) {
247 null_header = BSWAP32(null_header);
251 * The null header value must be greater than the IEEE 802.3 maximum
252 * frame length to be a valid Ethernet type; if it is, hand it
253 * to "ethertype()", otherwise treat it as a BSD AF_type (we wire
254 * in the values of the BSD AF_ types, because the values
255 * in the file will be BSD values, and the OS on which
256 * we're building this might not have the same values or
257 * might not have them defined at all; XXX - what if different
258 * BSD derivatives have different values?).
260 if (null_header > IEEE_802_3_MAX_LEN) {
262 ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, FALSE);
263 fh_tree = proto_item_add_subtree(ti, ett_null);
266 ethertype(null_header, tvb, 4, pinfo, tree, fh_tree, hf_null_etype, -1);
268 /* populate a tree in the second pane with the status of the link
271 ti = proto_tree_add_item(tree, proto_null, tvb, 0, 4, FALSE);
272 fh_tree = proto_item_add_subtree(ti, ett_null);
273 proto_tree_add_uint(fh_tree, hf_null_family, tvb, 0, 4, null_header);
276 next_tvb = tvb_new_subset(tvb, 4, -1, -1);
277 if (!dissector_try_port(null_dissector_table, null_header,
278 next_tvb, pinfo, tree)) {
279 /* No sub-dissector found. Label rest of packet as "Data" */
280 dissect_data(next_tvb, 0, pinfo, tree);
287 proto_register_null(void)
289 static hf_register_info hf[] = {
291 /* registered here but handled in ethertype.c */
293 { "Type", "null.type", FT_UINT16, BASE_HEX, VALS(etype_vals), 0x0,
297 { "Family", "null.family", FT_UINT32, BASE_HEX, VALS(family_vals), 0x0,
300 static gint *ett[] = {
304 proto_null = proto_register_protocol("Null/Loopback", "Null", "null");
305 proto_register_field_array(proto_null, hf, array_length(hf));
306 proto_register_subtree_array(ett, array_length(ett));
308 /* subdissector code */
309 null_dissector_table = register_dissector_table("null.type");
313 proto_reg_handoff_null(void)
316 * Get a handle for the PPP-in-HDLC-like-framing dissector.
318 ppp_hdlc_handle = find_dissector("ppp_hdlc");
319 dissector_add("wtap_encap", WTAP_ENCAP_NULL, dissect_null, proto_null);