我使用的libpcap函數pcap_next()來捕獲來自其他主機 一些TCP包我檢查捕獲的數據包 的字節並注意 數據包的以太網和IP報頭是扭曲的,在很多0的亂七八糟,但TCP頭很好爲什麼分組的以太網和IP報頭,其通過libpcap的功能捕獲,被扭曲
這是什麼原因?
代碼:
pcap_t* create_pcap_handler()
{
pcap_t *handle; /* Session handle */
char *dev; /* The device to sniff on */
char errbuf[PCAP_ERRBUF_SIZE]; /* Error string */
struct bpf_program fp; /* The compiled filter */
char filter_exp[] = "port 32000"; /* The filter expression */
bpf_u_int32 mask; /* Our netmask */
bpf_u_int32 net; /* Our IP subnet*/
/* Define the device */
dev = pcap_lookupdev(errbuf);
if (dev == NULL) {
fprintf(stderr, "Couldn't find default device: %s\n", errbuf);
exit(2);
}
/* Find the properties for the device */
if (pcap_lookupnet(dev, &net, &mask, errbuf) == -1) {
fprintf(stderr, "Couldn't get netmask for device %s: %s\n", dev, errbuf);
net = 0;
mask = 0;
}
struct in_addr tmp;
tmp.s_addr=net;
char IPdotdec[20];
inet_ntop(AF_INET, (void *)&tmp, IPdotdec, 16);
printf("net is %s\n", IPdotdec);
tmp.s_addr=mask;
inet_ntop(AF_INET, (void *)&tmp, IPdotdec, 16);
printf("mask is %s\n", IPdotdec);
printf("dev is %s\n",dev);
handle = pcap_open_live(dev, BUFSIZ, 0, 0, errbuf);
if (handle == NULL) {
fprintf(stderr, "Couldn't open device %s: %s\n", dev, errbuf);
exit(2) ;
}
/* Compile and apply the filter */
if (pcap_compile(handle, &fp, filter_exp, 0, mask) == -1) {
fprintf(stderr, "Couldn't parse filter %s: %s\n", filter_exp, pcap_geterr(handle));
exit(2);
}
if (pcap_setfilter(handle, &fp) == -1) {
fprintf(stderr, "Couldn't install filter %s: %s\n", filter_exp, pcap_geterr(handle));
exit(2);
}
return handle;
}
和主要功能
int main()
{
pcap_t * pcap_handler=create_pcap_handler();
struct pcap_pkthdr pcap_header; /* The header that pcap gives us */
const u_char *pcap_packet; /* The actual packet */
pcap_packet = pcap_next(pcap_handler, &pcap_header);
if(pcap_packet !=NULL)
printf("capture one packet with length of %d\n", pcap_header.len);
pcap_close(pcap_handler);
return 0;
}
這是用於傳入還是傳出的數據包?對於傳出數據包,這些圖層的捕獲可能是錯誤的,因爲有些數據可能會在捕獲後由網卡填充。 – wldsvc 2013-03-15 16:24:06
傳入數據包,我也用tcpdump捕獲了tcp數據包,那些數據包都很好 – user1944267 2013-03-15 16:25:27
你能提供樣例代碼嗎? – wldsvc 2013-03-15 16:39:46