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/* $OpenBSD: print-gre.c,v 1.2 2000/10/03 14:31:57 ho Exp $ */
/*
* 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: /cvs/OpenBSD/src/usr.sbin/tcpdump/print-gre.c,v 1.2 2000/10/03 14:31:57 ho Exp $";
#endif
#include <sys/param.h>
#include <sys/time.h>
#include <sys/uio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netdb.h>
#include <stdio.h>
#include "interface.h"
#include "addrtoname.h"
#include "extract.h" /* must come after interface.h */
#define GRE_SIZE (20)
struct gre {
u_short flags;
u_short proto;
union {
struct gre_ckof {
u_short cksum;
u_short offset;
} gre_ckof;
u_int32_t key;
u_int32_t seq;
} gre_void1;
union {
u_int32_t key;
u_int32_t seq;
u_int32_t routing;
} gre_void2;
union {
u_int32_t seq;
u_int32_t routing;
} gre_void3;
union {
u_int32_t routing;
} gre_void4;
};
#define GRE_CP 0x8000 /* Checksum Present */
#define GRE_RP 0x4000 /* Routing Present */
#define GRE_KP 0x2000 /* Key Present */
#define GRE_SP 0x1000 /* Sequence Present */
#define GREPROTO_IP 0x0800
/*
* 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_short flags, proto;
gre = (const struct gre *)bp;
if (length < GRE_SIZE) {
goto trunc;
}
flags = EXTRACT_16BITS(&gre->flags);
proto = EXTRACT_16BITS(&gre->proto);
if (vflag) {
/* 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');
fputs("] ", stdout);
}
/* Checksum & Offset are present */
if ((flags & GRE_CP) | (flags & GRE_RP))
cp += 4;
/* We don't support routing fields (variable length) now. Punt. */
if (flags & GRE_RP)
return;
if (flags & GRE_KP)
cp += 4;
if (flags & GRE_SP)
cp += 4;
switch (proto) {
case GREPROTO_IP:
ip_print(cp, length - ((cp - bp) / sizeof(u_char)));
break;
default:
printf("gre-proto-0x%04X", proto);
break;
}
return;
trunc:
fputs("[|gre]", stdout);
}
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