l2tp.c

该程序类似于tcpdump软件

/**************************************************************************** 
 **
 ** File: l2tp.c
 **
 ** Author: Mike Borella
 **
 ** Comments: Dump L2TP header information
 **
 ****************************************************************************/

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <string.h>
#include "config.h"
#include "l2tp.h"

/*
 * Control message types 
 */

char *CtrlMsgType[17] =
{
  "",
  "Start Ctrl Conn Request",
  "Start Ctrl Conn Reply",
  "Start Ctrl Conn Connected",
  "Stop Ctrl Conn Notification",
  "(Reserved)",
  "Hello",
  "Outgoing Call Request",
  "Outgoing Call Reply",
  "Outgoing Call Connected",
  "Incoming Call Request",
  "Incoming Call Reply",
  "Incoming Call Connected",
  "(Reserved)",
  "Call Disconnect Notify",
  "WAN Error Notify",
  "Set Link Info"
};

/*
 * Message type AVP (generic part)
 */

typedef struct _L2TP_AVP
{
#if defined(WORDS_BIGENDIAN)
  u_int16_t m:1,
            h:1,
            zeros:4,
            length:10;
#else
  u_int16_t length:10,
            zeros:4,
            h:1,
            m:1;
#endif
  u_int16_t vendorID;
  u_int16_t attribute;
} L2TP_AVP;


/*
 * L2TP control Header (generic part)
 */

typedef struct _L2TPCtrlHdr
{
  u_int8_t bits;
  u_int8_t version;
  u_int16_t length;
  u_int16_t tunnelID;
  u_int16_t callID;
  u_int16_t ns;
  u_int16_t nr;
} L2TPCtrlHdr;

extern u_char *packet_end;

/*----------------------------------------------------------------------------
**
** dump_l2tp()
**
** Parse L2TP packet and dump fields
**
**----------------------------------------------------------------------------
*/

void dump_l2tp(u_char *bp, int length)
{
  u_char *ep = bp + length;
  u_char *p;
  u_char type;
  int len;
  int AVP_len;
  L2TPCtrlHdr *ch;
  int parse_AVP(u_char *, u_char *);

  /*
   * Make sure we don't run off the end of the packet
   */

  if (ep > packet_end) 
    ep = packet_end;
  p = bp;

  /*
   * Determine type: either control or data
   */

  type = *p && 0x80;
  if (type == 0)
    {
      /*
       * Parse and print data packet headers
       */

      printf("----------------------------------------------------------\n");
      printf("                        L2TP Data Header\n");
      printf("----------------------------------------------------------\n");

    }

  else

    {
      /*
       * Parse and print control packet headers
       */
      
      ch = (L2TPCtrlHdr *) p;

      printf("----------------------------------------------------------\n");
      printf("                        L2TP Control Header\n");
      printf("----------------------------------------------------------\n");
      
      /*
       * Check for valid bits
       */
      
      if (ch->bits != 0xc8)
	{
	  printf("Invalid TLF bits\n");
	  return;
	}

      printf("Version:                %d\n", ch->version);
      len = ntohs(ch->length);
      printf("Length:                 %d\n", len);
      printf("Tunnel ID:              %d\n", ntohs(ch->tunnelID));
      printf("Call ID:                %d\n", ntohs(ch->callID)); 
      printf("Next Sent:              %d\n", ntohs(ch->ns));
      printf("Next Received:          %d\n", ntohs(ch->nr));
      
      p += sizeof(L2TPCtrlHdr);
      AVP_len = parse_AVP(p, ep);
    }
}

/*----------------------------------------------------------------------------
**
** parse_AVP()
**
** Parse L2TP AVP subheader
**
**----------------------------------------------------------------------------
*/

int parse_AVP(u_char *p, u_char *ep)
{
  L2TP_AVP *avp;
  u_char *p2;
  u_int16_t val;
  void dump_AVP(L2TP_AVP *, char *);
  
  avp = (L2TP_AVP *) p;
  
  switch(avp->attribute)
    {
    case 0:
      dump_AVP(avp, "Message Type");
      p2 = p+sizeof(L2TP_AVP);
      val = EXTRACT_16BITS(p2);
      printf("Value:                  %d (%s)\n", val, CtrlMsgType[val]);
      break;

    case 1:
      dump_AVP(avp, "Result Code");
      break;

    case 2:
      dump_AVP(avp, "Protocol Version");
      break;
      
    case 3: 
      dump_AVP(avp, "Framing Capabilities");
      break;
      
    case 4:
      dump_AVP(avp, "Bearer Capabilities");
      break;

    case 5:
      dump_AVP(avp, "Tiebreaker");
      break;

    case 6:
      dump_AVP(avp, "Firmware Revision");
      break;

    case 7: 
      dump_AVP(avp, "Host Name");
      break;

    case 8:
      dump_AVP(avp, "Vendor Name");
      break;

    case 9:
      dump_AVP(avp, "Assigned Tunnel ID");
      break;

    case 10:
      dump_AVP(avp, "Receive Window Size");
      break;

    case 14:
      dump_AVP(avp, "Assigned Call ID");
      break;


    default: 
      return -1;
      
    }

  return avp->length;
}


/*----------------------------------------------------------------------------
**
** dump_AVP()
**
** Print L2TP AVP subheader
**
**----------------------------------------------------------------------------
*/

void dump_AVP(L2TP_AVP *avp, char *name)
{
  printf("%s AVP\n", name);
  printf("  M bit:                %d\n", avp->m);
  printf("  H bit:                %d\n", avp->h);
  printf("  Zeros:                %d\n", avp->zeros);
  printf("  Length:               %d\n", avp->length);
  printf("  Vendor ID:            %d\n", avp->vendorID);
  printf("  Attribute:            %d\n", avp->attribute);
}