1 /*
2 * Copyright (c) 1990, 1991, 1993, 1994, 1995, 1996, 1997
3 * The Regents of the University of California. All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that: (1) source code distributions
7 * retain the above copyright notice and this paragraph in its entirety, (2)
8 * distributions including binary code include the above copyright notice and
9 * this paragraph in its entirety in the documentation or other materials
10 * provided with the distribution, and (3) all advertising materials mentioning
11 * features or use of this software display the following acknowledgement:
12 * ``This product includes software developed by the University of California,
13 * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
14 * the University nor the names of its contributors may be used to endorse
15 * or promote products derived from this software without specific prior
16 * written permission.
17 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
18 * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
19 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
20 */
21
22 /* \summary: PPP Van Jacobson compression printer */
23
24 /* specification: RFC 1144 */
25
26 #ifdef HAVE_CONFIG_H
27 #include <config.h>
28 #endif
29
30 #include "netdissect-stdinc.h"
31
32 #include "netdissect.h"
33 #include "extract.h"
34 #include "slcompress.h"
35 #include "ppp.h"
36
37 /*
38 * XXX - for BSD/OS PPP, what packets get supplied with a PPP header type
39 * of PPP_VJC and what packets get supplied with a PPP header type of
40 * PPP_VJNC? PPP_VJNC is for "UNCOMPRESSED_TCP" packets, and PPP_VJC
41 * is for COMPRESSED_TCP packets (PPP_IP is used for TYPE_IP packets).
42 *
43 * RFC 1144 implies that, on the wire, the packet type is *not* needed
44 * for PPP, as different PPP protocol types can be used; it only needs
45 * to be put on the wire for SLIP.
46 *
47 * It also indicates that, for compressed SLIP:
48 *
49 * If the COMPRESSED_TCP bit is set in the first byte, it's
50 * a COMPRESSED_TCP packet; that byte is the change byte, and
51 * the COMPRESSED_TCP bit, 0x80, isn't used in the change byte.
52 *
53 * If the upper 4 bits of the first byte are 7, it's an
54 * UNCOMPRESSED_TCP packet; that byte is the first byte of
55 * the UNCOMPRESSED_TCP modified IP header, with a connection
56 * number in the protocol field, and with the version field
57 * being 7, not 4.
58 *
59 * Otherwise, the packet is an IPv4 packet (where the upper 4 bits
60 * of the packet are 4).
61 *
62 * So this routine looks as if it's sort-of intended to handle
63 * compressed SLIP, although it doesn't handle UNCOMPRESSED_TCP
64 * correctly for that (it doesn't fix the version number and doesn't
65 * do anything to the protocol field), and doesn't check for COMPRESSED_TCP
66 * packets correctly for that (you only check the first bit - see
67 * B.1 in RFC 1144).
68 *
69 * But it's called for BSD/OS PPP, not SLIP - perhaps BSD/OS does weird
70 * things with the headers?
71 *
72 * Without a BSD/OS VJC-compressed PPP trace, or knowledge of what the
73 * BSD/OS VJC code does, we can't say what's the case.
74 *
75 * We therefore leave "proto" - which is the PPP protocol type - in place,
76 * *not* marked as unused, for now, so that GCC warnings about the
77 * unused argument remind us that we should fix this some day.
78 *
79 * XXX - also, it fetches the TCP checksum field in COMPRESSED_TCP
80 * packets with GET_HE_U_2, rather than with GET_BE_U_2(); RFC 1144 says
81 * it's "the unmodified TCP checksum", which would imply that it's
82 * big-endian, but perhaps, on the platform where this was developed,
83 * the packets were munged by the networking stack before being handed
84 * to the packet capture mechanism.
85 */
86 int
vjc_print(netdissect_options * ndo,const u_char * bp,u_short proto _U_)87 vjc_print(netdissect_options *ndo, const u_char *bp, u_short proto _U_)
88 {
89 int i;
90
91 ndo->ndo_protocol = "vjc";
92 switch (GET_U_1(bp) & 0xf0) {
93 case TYPE_IP:
94 if (ndo->ndo_eflag)
95 ND_PRINT("(vjc type=IP) ");
96 return PPP_IP;
97 case TYPE_UNCOMPRESSED_TCP:
98 if (ndo->ndo_eflag)
99 ND_PRINT("(vjc type=raw TCP) ");
100 return PPP_IP;
101 case TYPE_COMPRESSED_TCP:
102 if (ndo->ndo_eflag)
103 ND_PRINT("(vjc type=compressed TCP) ");
104 for (i = 0; i < 8; i++) {
105 if (GET_U_1(bp + 1) & (0x80 >> i))
106 ND_PRINT("%c", "?CI?SAWU"[i]);
107 }
108 if (GET_U_1(bp + 1))
109 ND_PRINT(" ");
110 ND_PRINT("C=0x%02x ", GET_U_1(bp + 2));
111 ND_PRINT("sum=0x%04x ", GET_HE_U_2(bp + 3));
112 return -1;
113 case TYPE_ERROR:
114 if (ndo->ndo_eflag)
115 ND_PRINT("(vjc type=error) ");
116 return -1;
117 default:
118 if (ndo->ndo_eflag)
119 ND_PRINT("(vjc type=0x%02x) ", GET_U_1(bp) & 0xf0);
120 return -1;
121 }
122 }
123