43     void ip_packet::checksum(void *packet)
 44     {
 45         struct ip *ip_hdr = (struct ip*) packet;
 46
 47         uint16_t checksum = 0;
 48         uint16_t *buffer;
 49         for (int i = 0; i < ip_hdr->ip_len * 2; i++) {
 50             buffer = (uint16_t*) ((char*) packet + i * sizeof (*buffer));
 51             checksum += *buffer & 0xFFFF;
 52         }
 53         ip_hdr->ip_sum = checksum;
 54     }