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 1.9 2000-12-18 05:41:59 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
  41 #include <netdb.h>
  42 #include <stdio.h>
  43
  44 #include "interface.h"
  45 #include "addrtoname.h"
  46 #include "extract.h"            /* must come after interface.h */
  47
  48 #define GRE_SIZE (20)
  49
  50 struct gre {
  51         u_short flags;
  52         u_short proto;
  53         union {
  54                 struct gre_ckof {
  55                         u_short cksum;
  56                         u_short offset;
  57                 }        gre_ckof;
  58                 u_int32_t key;
  59                 u_int32_t seq;
  60         }     gre_void1;
  61         union {
  62                 u_int32_t key;
  63                 u_int32_t seq;
  64                 u_int32_t routing;
  65         }     gre_void2;
  66         union {
  67                 u_int32_t seq;
  68                 u_int32_t routing;
  69         }     gre_void3;
  70         union {
  71                 u_int32_t routing;
  72         }     gre_void4;
  73 };
  74
  75 #define GRE_CP          0x8000  /* Checksum Present */
  76 #define GRE_RP          0x4000  /* Routing Present */
  77 #define GRE_KP          0x2000  /* Key Present */
  78 #define GRE_SP          0x1000  /* Sequence Present */
  79
  80
  81 /*
  82  * Deencapsulate and print a GRE-tunneled IP datagram
  83  */
  84 void
  85 gre_print(const u_char *bp, u_int length)
  86 {
  87         const u_char *cp = bp + 4;
  88         const struct gre *gre;
  89         u_short flags, proto, extracted_ethertype;
  90
  91         gre = (const struct gre *)bp;
  92
  93         if (length < GRE_SIZE) {
  94                 goto trunc;
  95         }
  96         flags = EXTRACT_16BITS(&gre->flags);
  97         proto = EXTRACT_16BITS(&gre->proto);
  98
  99         if (vflag) {
 100                 /* Decode the flags */
 101                 putchar('[');
 102                 if (flags & GRE_CP)
 103                         putchar('C');
 104                 if (flags & GRE_RP)
 105                         putchar('R');
 106                 if (flags & GRE_KP)
 107                         putchar('K');
 108                 if (flags & GRE_SP)
 109                         putchar('S');
 110                 fputs("] ", stdout);
 111         }
 112         /* Checksum & Offset are present */
 113         if ((flags & GRE_CP) | (flags & GRE_RP))
 114                 cp += 4;
 115
 116         /* We don't support routing fields (variable length) now. Punt. */
 117         if (flags & GRE_RP)
 118                 return;
 119
 120         if (flags & GRE_KP)
 121                 cp += 4;
 122         if (flags & GRE_SP)
 123                 cp += 4;
 124
 125         length -= cp - bp;
 126         if (ether_encap_print(proto, cp, length, length,
 127             &extracted_ethertype) == 0)
 128                 printf("gre-proto-0x%04X", proto);
 129         return;
 130
 131 trunc:
 132         fputs("[|gre]", stdout);
 133
 134 }