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 1.7 2000-09-23 08:54:29 guy 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
  42 #include <netdb.h>
  43 #include <stdio.h>
  44
  45 #include "interface.h"
  46 #include "addrtoname.h"
  47 #include "extract.h"            /* must come after interface.h */
  48
  49 #define GRE_SIZE (20)
  50
  51 struct gre {
  52         u_short flags;
  53         u_short proto;
  54         union {
  55                 struct gre_ckof {
  56                         u_short cksum;
  57                         u_short offset;
  58                 }        gre_ckof;
  59                 u_int32_t key;
  60                 u_int32_t seq;
  61         }     gre_void1;
  62         union {
  63                 u_int32_t key;
  64                 u_int32_t seq;
  65                 u_int32_t routing;
  66         }     gre_void2;
  67         union {
  68                 u_int32_t seq;
  69                 u_int32_t routing;
  70         }     gre_void3;
  71         union {
  72                 u_int32_t routing;
  73         }     gre_void4;
  74 };
  75
  76 #define GRE_CP          0x8000  /* Checksum Present */
  77 #define GRE_RP          0x4000  /* Routing Present */
  78 #define GRE_KP          0x2000  /* Key Present */
  79 #define GRE_SP          0x1000  /* Sequence Present */
  80
  81
  82 /*
  83  * Deencapsulate and print a GRE-tunneled IP datagram
  84  */
  85 void
  86 gre_print(const u_char *bp, u_int length)
  87 {
  88         const u_char *cp = bp + 4;
  89         const struct gre *gre;
  90         u_short flags, proto;
  91
  92         gre = (const struct gre *)bp;
  93
  94         if (length < GRE_SIZE) {
  95                 goto trunc;
  96         }
  97         flags = EXTRACT_16BITS(&gre->flags);
  98         proto = EXTRACT_16BITS(&gre->proto);
  99
 100         if (vflag) {
 101                 /* Decode the flags */
 102                 putchar('[');
 103                 if (flags & GRE_CP)
 104                         putchar('C');
 105                 if (flags & GRE_RP)
 106                         putchar('R');
 107                 if (flags & GRE_KP)
 108                         putchar('K');
 109                 if (flags & GRE_SP)
 110                         putchar('S');
 111                 fputs("] ", stdout);
 112         }
 113         /* Checksum & Offset are present */
 114         if ((flags & GRE_CP) | (flags & GRE_RP))
 115                 cp += 4;
 116
 117         /* We don't support routing fields (variable length) now. Punt. */
 118         if (flags & GRE_RP)
 119                 return;
 120
 121         if (flags & GRE_KP)
 122                 cp += 4;
 123         if (flags & GRE_SP)
 124                 cp += 4;
 125
 126         length -= cp - bp;
 127         if (ether_encap_print(proto, cp, length, length) == 0)
 128                 printf("gre-proto-0x%04X", proto);
 129         return;
 130
 131 trunc:
 132         fputs("[|gre]", stdout);
 133
 134 }