usr/src/sys/netinet/udp.h

/*      udp.h   4.3     81/11/18        */

/*
 * Udp protocol header.
 * Per RFC 768, September, 1981.
 */
struct udphdr {
        u_short uh_sport;               /* source port */
        u_short uh_dport;               /* destination port */
        short   uh_ulen;                /* udp length */
        u_short uh_sum;                 /* udp checksum */
};