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 "slcompress.h"
34 #include "ppp.h"
35
36 /*
37 * XXX - for BSD/OS PPP, what packets get supplied with a PPP header type
38 * of PPP_VJC and what packets get supplied with a PPP header type of
39 * PPP_VJNC? PPP_VJNC is for "UNCOMPRESSED_TCP" packets, and PPP_VJC
40 * is for COMPRESSED_TCP packets (PPP_IP is used for TYPE_IP packets).
41 *
42 * RFC 1144 implies that, on the wire, the packet type is *not* needed
43 * for PPP, as different PPP protocol types can be used; it only needs
44 * to be put on the wire for SLIP.
45 *
46 * It also indicates that, for compressed SLIP:
47 *
48 * If the COMPRESSED_TCP bit is set in the first byte, it's
49 * a COMPRESSED_TCP packet; that byte is the change byte, and
50 * the COMPRESSED_TCP bit, 0x80, isn't used in the change byte.
51 *
52 * If the upper 4 bits of the first byte are 7, it's an
53 * UNCOMPRESSED_TCP packet; that byte is the first byte of
54 * the UNCOMPRESSED_TCP modified IP header, with a connection
55 * number in the protocol field, and with the version field
56 * being 7, not 4.
57 *
58 * Otherwise, the packet is an IPv4 packet (where the upper 4 bits
59 * of the packet are 4).
60 *
61 * So this routine looks as if it's sort-of intended to handle
62 * compressed SLIP, although it doesn't handle UNCOMPRESSED_TCP
63 * correctly for that (it doesn't fix the version number and doesn't
64 * do anything to the protocol field), and doesn't check for COMPRESSED_TCP
65 * packets correctly for that (you only check the first bit - see
66 * B.1 in RFC 1144).
67 *
68 * But it's called for BSD/OS PPP, not SLIP - perhaps BSD/OS does weird
69 * things with the headers?
70 *
71 * Without a BSD/OS VJC-compressed PPP trace, or knowledge of what the
72 * BSD/OS VJC code does, we can't say what's the case.
73 *
74 * We therefore leave "proto" - which is the PPP protocol type - in place,
75 * *not* marked as unused, for now, so that GCC warnings about the
76 * unused argument remind us that we should fix this some day.
77 *
78 * XXX - also, it fetches the TCP checksum field in COMPRESSED_TCP
79 * packets directly, rather than with EXTRACT_16BITS(); RFC 1144 says
80 * it's "the unmodified TCP checksum", which would imply that it's
81 * big-endian, but perhaps, on the platform where this was developed,
82 * the packets were munged by the networking stack before being handed
83 * to the packet capture mechanism.
84 */
85 int
vjc_print(netdissect_options * ndo,register const char * bp,u_short proto _U_)86 vjc_print(netdissect_options *ndo, register const char *bp, u_short proto _U_)
87 {
88 int i;
89
90 switch (bp[0] & 0xf0) {
91 case TYPE_IP:
92 if (ndo->ndo_eflag)
93 ND_PRINT((ndo, "(vjc type=IP) "));
94 return PPP_IP;
95 case TYPE_UNCOMPRESSED_TCP:
96 if (ndo->ndo_eflag)
97 ND_PRINT((ndo, "(vjc type=raw TCP) "));
98 return PPP_IP;
99 case TYPE_COMPRESSED_TCP:
100 if (ndo->ndo_eflag)
101 ND_PRINT((ndo, "(vjc type=compressed TCP) "));
102 for (i = 0; i < 8; i++) {
103 if (bp[1] & (0x80 >> i))
104 ND_PRINT((ndo, "%c", "?CI?SAWU"[i]));
105 }
106 if (bp[1])
107 ND_PRINT((ndo, " "));
108 ND_PRINT((ndo, "C=0x%02x ", bp[2]));
109 ND_PRINT((ndo, "sum=0x%04x ", *(const u_short *)&bp[3]));
110 return -1;
111 case TYPE_ERROR:
112 if (ndo->ndo_eflag)
113 ND_PRINT((ndo, "(vjc type=error) "));
114 return -1;
115 default:
116 if (ndo->ndo_eflag)
117 ND_PRINT((ndo, "(vjc type=0x%02x) ", bp[0] & 0xf0));
118 return -1;
119 }
120 }
121