The Tcpdump Group git mirrors - tcpdump/blob - print-gre.c

   1 /*
   2  * Copyright (c) 1996
   3  *      The Regents of the University of California.  All rights reserved.
   4  *
   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.
  17  *
  18  * Initial contribution from John Hawkinson <jhawk@bbnplanet.com>
  19  *
  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.
  23  */
  24
  25 #ifndef lint
  26 static const char rcsid[] =
  27     "@(#) $Header: /tcpdump/master/tcpdump/print-gre.c,v 1.6 1999-11-21 09:36:52 fenner Exp $";
  28 #endif
  29
  30 #ifdef HAVE_CONFIG_H
  31 #include "config.h"
  32 #endif
  33
  34 #include <sys/param.h>
  35 #include <sys/time.h>
  36 #include <sys/uio.h>
  37 #include <sys/socket.h>
  38
  39 #include <netinet/in.h>
  40 #include <netinet/in_systm.h>
  41 #include <netinet/ip.h>
  42
  43 #include <netdb.h>
  44 #include <stdio.h>
  45
  46 #include "interface.h"
  47 #include "addrtoname.h"
  48 #include "extract.h"            /* must come after interface.h */
  49
  50 #define GRE_SIZE (20)
  51
  52 struct gre {
  53         u_short flags;
  54         u_short proto;
  55         union {
  56                 struct gre_ckof {
  57                         u_short cksum;
  58                         u_short offset;
  59                 }        gre_ckof;
  60                 u_int32_t key;
  61                 u_int32_t seq;
  62         }     gre_void1;
  63         union {
  64                 u_int32_t key;
  65                 u_int32_t seq;
  66                 u_int32_t routing;
  67         }     gre_void2;
  68         union {
  69                 u_int32_t seq;
  70                 u_int32_t routing;
  71         }     gre_void3;
  72         union {
  73                 u_int32_t routing;
  74         }     gre_void4;
  75 };
  76
  77 #define GRE_CP          0x8000  /* Checksum Present */
  78 #define GRE_RP          0x4000  /* Routing Present */
  79 #define GRE_KP          0x2000  /* Key Present */
  80 #define GRE_SP          0x1000  /* Sequence Present */
  81
  82
  83 /*
  84  * Deencapsulate and print a GRE-tunneled IP datagram
  85  */
  86 void
  87 gre_print(const u_char *bp, u_int length)
  88 {
  89         const u_char *cp = bp + 4;
  90         const struct gre *gre;
  91         u_short flags, proto;
  92
  93         gre = (const struct gre *)bp;
  94
  95         if (length < GRE_SIZE) {
  96                 goto trunc;
  97         }
  98         flags = EXTRACT_16BITS(&gre->flags);
  99         proto = EXTRACT_16BITS(&gre->proto);
 100
 101         if (vflag) {
 102                 /* Decode the flags */
 103                 putchar('[');
 104                 if (flags & GRE_CP)
 105                         putchar('C');
 106                 if (flags & GRE_RP)
 107                         putchar('R');
 108                 if (flags & GRE_KP)
 109                         putchar('K');
 110                 if (flags & GRE_SP)
 111                         putchar('S');
 112                 fputs("] ", stdout);
 113         }
 114         /* Checksum & Offset are present */
 115         if ((flags & GRE_CP) | (flags & GRE_RP))
 116                 cp += 4;
 117
 118         /* We don't support routing fields (variable length) now. Punt. */
 119         if (flags & GRE_RP)
 120                 return;
 121
 122         if (flags & GRE_KP)
 123                 cp += 4;
 124         if (flags & GRE_SP)
 125                 cp += 4;
 126
 127         length -= cp - bp;
 128         if (ether_encap_print(proto, cp, length, length) == 0)
 129                 printf("gre-proto-0x%04X", proto);
 130         return;
 131
 132 trunc:
 133         fputs("[|gre]", stdout);
 134
 135 }