Hello All,
I am trying to write an application using pcap in windows which acts like a Network Layer 2 switch. This is what I am doing. 1. PC A has 1 LAN card 2. PC B has 2 LAN cards 3. PC C has 1 LAN card I Connect PC A to PC B over LAN 1 and connect PC C and PC B over LAN 2. LAN cards in PC B are NOT bridged. So when I send data from PC A to PC C, it will not reach the destination. Application that I wrote does the following: Let's assume PC A is connected to LAN card 1 in PC B and PC C is connected to LAN card 2 in PC B. When PC A sends data intended for PC C, application running on PC B, using PCAP api's receives the Data link layer data at the application layer through LAN card 1 and forwards the same without modifying to PC C through LAN card 2 using pcap api's and vice versa. I could verify that data sent by PC A is received by LAN card 1 by observing the contents of the packet received in the application. Api used to transmit the same packet over LAN card 2 return success but when I ran ethereal on PC C to capture all packets received I don't see the packet that was forwarded by PC B. I used pcap library in PC B and ethereal in PC C in promiscuous mode. Am I missing something??????? I have also attached the source code. Please take a look and let me know if I missed something. Thanks & Regards Shakthi E-Mail : [EMAIL PROTECTED] <skype:t.shakthi.pradeep?call>
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#include "include/pcap.h"
void PacketReceiver_A(unsigned char *, const struct pcap_pkthdr *, const
unsigned char *);
void PacketReceiver_B(unsigned char *, const struct pcap_pkthdr *, const
unsigned char *);
int OpenAndRegisterCallBackWithInterfaceA(struct PcapInfo *);
int OpenAndRegisterCallBackWithInterfaceB(struct PcapInfo *);
pcap_if_t *SelectInterface(pcap_if_t *,int );
void DexExit(pcap_if_t *);
struct PcapInfo
{
pcap_if_t *alldevs;
pcap_if_t *d;
}pcapinfoA,pcapinfoB;
pcap_t *adhandleA,*adhandleB;
void DexExit(pcap_if_t *alldevs)
{
getch();
/* At this point, we don't need any more the device list. Free it */
pcap_freealldevs(alldevs);
exit(0);
}
main()
{
pcap_if_t *alldevs;
pcap_if_t *d, *dA, *dB;
int inum;
int i=0;
pcap_t *adhandleA,*adhandleB;
char errbuf[PCAP_ERRBUF_SIZE];
HANDLE InterfaceA,InterfaceB;
int InterfaceAStatus,InterfaceBStatus;
/* Retrieve the device list */
if(pcap_findalldevs(&alldevs, errbuf) == -1)
{
fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);
DexExit(alldevs);
}
/* Print the list */
for(d=alldevs; d; d=d->next)
{
printf("%d. %s", ++i, d->name);
if (d->description)
printf(" (%s)\n\n", d->description);
else
printf(" (No description available)\n");
}
if(i==0)
{
printf("\nNo interfaces found! Make sure WinPcap is
installed.\n");
DexExit(alldevs);
}
/* Select Interface A */
dA = SelectInterface(alldevs,i);
if(dA == -1)
{
printf("Selected Wrong Interface\n");
DexExit(alldevs);
}
/* Select Interface B */
dB = SelectInterface(alldevs,i);
if(dB == -1)
{
printf("Selected Wrong Interface\n");
DexExit(alldevs);
}
/* check if both selected interfaces are same */
if(dA == dB)
{
printf("Selected Same Interface\nPlease select different
Interfaces\n");
DexExit(alldevs);
}
/* Create threadto Hadle Interface A */
pcapinfoA.alldevs = alldevs;
pcapinfoA.d = dA;
InterfaceAStatus = CreateThread(
NULL, // default security attributes
0, // use default stack size
(void *)OpenAndRegisterCallBackWithInterfaceA, // thread
function
&pcapinfoA, // argument to thread function
0, // use default creation flags
&InterfaceA); // returns the thread identifier
if(InterfaceAStatus)
{
printf("Interface A Handler started.\n");
}
else
{
printf("Interface A Handler start failed\n");
DexExit(alldevs);
}
/* Create threadto Hadle Interface A */
pcapinfoB.alldevs = alldevs;
pcapinfoB.d = dB;
InterfaceBStatus = CreateThread(
NULL, // default security attributes
0, // use default stack size
(void *)OpenAndRegisterCallBackWithInterfaceB, // thread
function
&pcapinfoB, // argument to thread function
0, // use default creation flags
&InterfaceB); // returns the thread identifier
if(InterfaceAStatus)
{
printf("Interface B Handler started.\n");
}
else
{
printf("Interface B Handler start failed\n");
DexExit(alldevs);
}
//WaitForSingleObject(InterfaceA,INFINITE);
//WaitForSingleObject(InterfaceB,INFINITE);
while(1) Sleep(1);
return 0;
}
pcap_if_t *SelectInterface(pcap_if_t *alldevs,int numinterfaces)
{
int inum=-1;
pcap_if_t *d;
/* Request to select interface */
printf("Enter the interface number A (1-%d):",numinterfaces);
scanf("%d", &inum);
if(inum < 1 || inum > numinterfaces)
{
printf("\nInterface number out of range.\n");
/* Free the device list */
pcap_freealldevs(alldevs);
return -1;
}
/* Jump to the selected adapter */
for(d=alldevs, numinterfaces=0; numinterfaces< inum-1 ;d=d->next,
numinterfaces++);
return d;
}
int OpenAndRegisterCallBackWithInterfaceA(struct PcapInfo *InterfaceInfoA)
{
int inum;
int i=0;
char errbuf[PCAP_ERRBUF_SIZE];
/* Open the device A*/
/* Open the adapter A*/
if ((adhandleA= pcap_open_live(InterfaceInfoA->d->name, // name of the
device
65536,
// portion of the packet to capture.
// 65536 grants that the whole packet will be captured on all the MACs.
1,
// promiscuous mode (nonzero means promiscuous)
1000,
// read timeout
errbuf
// error buffer
)) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not
supported by WinPcap\n", InterfaceInfoA->d->name);
/* Free the device list */
pcap_freealldevs(InterfaceInfoA->alldevs);
return -1;
}
printf("\nlistening on %s...\n\n", InterfaceInfoA->d->description);
/* start the capture */
pcap_loop(adhandleA, 0, PacketReceiver_A, NULL);
pcap_close(adhandleA);
return 0;
}
int OpenAndRegisterCallBackWithInterfaceB(struct PcapInfo *InterfaceInfoB)
{
int inum;
int i=0;
char errbuf[PCAP_ERRBUF_SIZE];
/* Open the device B*/
/* Open the adapter B*/
if ((adhandleB= pcap_open_live(InterfaceInfoB->d->name, // name of the
device
65536,
// portion of the packet to capture.
// 65536 grants that the whole packet will be captured on all the MACs.
1,
// promiscuous mode (nonzero means promiscuous)
1000,
// read timeout
errbuf
// error buffer
)) == NULL)
{
fprintf(stderr,"\nUnable to open the adapter. %s is not
supported by WinPcap\n", InterfaceInfoB->d->name);
/* Free the device list */
pcap_freealldevs(InterfaceInfoB->alldevs);
return -1;
}
printf("\nlistening on %s...\n\n", InterfaceInfoB->d->description);
/* start the capture */
pcap_loop(adhandleB, 0, PacketReceiver_B, NULL);
pcap_close(adhandleB);
return 0;
}
/* Callback function invoked by libpcap for every incoming packet on Interface
A*/
void PacketReceiver_A(unsigned char *param, const struct pcap_pkthdr *header,
const unsigned char *pkt_data)
{
printf("Interface A : len:%d\n",header->len);
/* Forward the packet on Interface B */
if (pcap_sendpacket(adhandleB, // Adapter
pkt_data, // buffer with the
packet
header->len // size
) != 0)
{
fprintf(stderr,"\nError sending the packet to Interface B: \n",
pcap_geterr(adhandleA));
return 3;
}
}
/* Callback function invoked by libpcap for every incoming packet on Interface
A*/
void PacketReceiver_B(unsigned char *param, const struct pcap_pkthdr *header,
const unsigned char *pkt_data)
{
printf("Interface B : len:%d\n",header->len);
/* Forward the packet on Interface B */
if (pcap_sendpacket(adhandleA, // Adapter
pkt_data, // buffer with the
packet
header->len // size
) != 0)
{
fprintf(stderr,"\nError sending the packet to Interface A: \n",
pcap_geterr(adhandleB));
return 3;
}
}
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