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/*
* Copyright (c) 1996
* The Regents of the University of California. All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Lawrence Berkeley Laboratory,
* Berkeley, CA. The name of the University may not be used to
* endorse or promote products derived from this software without
* specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*
* Initial contribution from John Hawkinson <jhawk@bbnplanet.com>
*
* This module implements support for decoding GRE (Generic Routing
* Encapsulation) tunnels; they're documented in RFC1701 and RFC1702.
* This code only supports the IP encapsulation thereof.
*/
#ifndef lint
static const char rcsid[] =
"@(#) $Header: /tcpdump/master/tcpdump/print-gre.c,v 1.13.4.1 2002/06/01 23:51:13 guy Exp $";
#endif
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <sys/param.h>
#include <sys/time.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <stdio.h>
#include "interface.h"
#include "addrtoname.h"
#include "extract.h" /* must come after interface.h */
struct gre {
u_int16_t flags;
u_int16_t proto;
};
/* RFC 2784 - GRE */
#define GRE_CP 0x8000 /* Checksum Present */
#define GRE_VER_MASK 0x0007 /* Version */
/* RFC 2890 - Key and Sequence extensions to GRE */
#define GRE_KP 0x2000 /* Key Present */
#define GRE_SP 0x1000 /* Sequence Present */
/* Legacy from RFC 1700 */
#define GRE_RP 0x4000 /* Routing Present */
#define GRE_sP 0x0800 /* strict source route present */
#define GRE_RECUR_MASK 0x0700 /* Recursion Control */
#define GRE_RECUR_SHIFT 8
#define GRE_COP (GRE_RP|GRE_CP) /* Checksum & Offset Present */
/* "Enhanced GRE" from RFC2637 - PPTP */
#define GRE_AP 0x0080 /* Ack present */
#define GRE_MBZ_MASK 0x0078 /* not defined */
/*
* Deencapsulate and print a GRE-tunneled IP datagram
*/
void
gre_print(const u_char *bp, u_int length)
{
const u_char *cp = bp + 4;
const struct gre *gre;
u_int16_t flags, proto;
u_short ver=0;
u_short extracted_ethertype;
gre = (const struct gre *)bp;
TCHECK(gre->proto);
flags = EXTRACT_16BITS(&gre->flags);
proto = EXTRACT_16BITS(&gre->proto);
(void)printf("gre ");
if (flags) {
/* Decode the flags */
putchar('[');
if (flags & GRE_CP)
putchar('C');
if (flags & GRE_RP)
putchar('R');
if (flags & GRE_KP)
putchar('K');
if (flags & GRE_SP)
putchar('S');
if (flags & GRE_sP)
putchar('s');
if (flags & GRE_AP)
putchar('A');
if (flags & GRE_RECUR_MASK)
printf("R%x", (flags & GRE_RECUR_MASK) >> GRE_RECUR_SHIFT);
ver = flags & GRE_VER_MASK;
printf("v%u", ver);
if (flags & GRE_MBZ_MASK)
printf("!%x", flags & GRE_MBZ_MASK);
fputs("] ", stdout);
}
if (flags & GRE_COP) {
int checksum, offset;
TCHECK2(*cp, 4);
checksum = EXTRACT_16BITS(cp);
offset = EXTRACT_16BITS(cp + 2);
if (flags & GRE_CP) {
/* Checksum present */
/* todo: check checksum */
if (vflag > 1)
printf("C:%04x ", checksum);
}
if (flags & GRE_RP) {
/* Offset present */
if (vflag > 1)
printf("O:%04x ", offset);
}
cp += 4; /* skip checksum and offset */
}
if (flags & GRE_KP) {
TCHECK2(*cp, 4);
if (ver == 1) { /* PPTP */
if (vflag > 1)
printf("PL:%u ", EXTRACT_16BITS(cp));
printf("ID:%04x ", EXTRACT_16BITS(cp+2));
}
else
printf("K:%08x ", EXTRACT_32BITS(cp));
cp += 4; /* skip key */
}
if (flags & GRE_SP) {
TCHECK2(*cp, 4);
printf("S:%u ", EXTRACT_32BITS(cp));
cp += 4; /* skip seq */
}
if (flags & GRE_AP && ver >= 1) {
TCHECK2(*cp, 4);
printf("A:%u ", EXTRACT_32BITS(cp));
cp += 4; /* skip ack */
}
/* We don't support routing fields (variable length) now. Punt. */
if (flags & GRE_RP)
return;
TCHECK(cp[0]);
length -= cp - bp;
if (ether_encap_print(proto, cp, length, length,
&extracted_ethertype) == 0)
printf("gre-proto-0x%04X", proto);
return;
trunc:
fputs("[|gre]", stdout);
}
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