IP6LEN
#define MAXDATALEN MAXPACKETLEN - IP6LEN - ICMP6ECHOLEN
packlen = 2048 + IP6LEN + ICMP6ECHOLEN + EXTRA;
packlen = datalen + IP6LEN + ICMP6ECHOLEN + EXTRA;
packlen = 2048 + IP6LEN + ICMP6ECHOLEN + EXTRA;