Libpcap is a portable packet capture library which is used in many packet sniffers, including Tcpdump.
You can download it from the following link: https://packetstormsecurity.com/files/download/23347/libpcap-0.5.2.tar.gz
Source: https://packetstormsecurity.com/files/23347/libpcap-0.5.2.tar.gz.html