#include <stdio.h>#include <pcap.h>#include <netinet/if_ether.h>int main(void){	pcap_t *sniffer_des;	char errbuf[PCAP_ERRBUF_SIZE];	char *net_dev;	bpf_u_int32 netp;	bpf_u_int32 maskp;	struct bpf_program fp;	const u_char *packet;	struct pcap_pkthdr hdr;	struct ether_header *eth_header;	u_char *ptr;		char filter_exp[]="port 22";	net_dev=pcap_lookupdev(errbuf);	if(net_dev==NULL){		printf("cannot get the network device info: %s\n",errbuf);		return 1;	}		if(pcap_lookupnet(net_dev,&netp,&maskp,errbuf)==-1){		printf("cannot get the network device ip info:%s\n",errbuf);		return 1;	}	sniffer_des=pcap_open_live(net_dev, 65535, 1, 1000, errbuf);	if(sniffer_des==NULL){		printf("cannot open the network device: %s\n",errbuf);		return 1;	}	if(pcap_compile(sniffer_des, &fp, filter_exp, 0, maskp)==-1){		printf("cannot compile the filter rule\n");		return 1;	}	if(pcap_setfilter(sniffer_des,&fp)==-1){		printf("cannot set the filter to the network device\n");		return 1;	}		packet=pcap_next(sniffer_des,&hdr);	if(packet==NULL){		printf("cannot get the packet\n");		return 1;	}	printf("Packet length: %d\n",hdr.len);	printf("Sniffer time: %s\n",ctime((const time_t*)&hdr.ts.tv_sec));	printf("length of portion present: %d\n",hdr.caplen);	eth_header=(struct ether_header*)packet;	if(ntohs(eth_header->ether_type)!=ETHERTYPE_IP){		printf("not ethernet packet\n ");		return 1;	}	ptr=eth_header->ether_dhost;	int i;	i=0;	printf("destination address(MAC):");	while(i<ETHER_ADDR_LEN){		printf(" %x ",*ptr++);		i++;	}		printf("\nsource address(MAC):");	ptr=eth_header->ether_shost;	i=0;	while(i<ETHER_ADDR_LEN){		printf(" %x ",*ptr++);		i++;	}	printf("\n");	return 0;}