ICMP6ECHOTMLEN
#define DEFDATALEN ICMP6ECHOTMLEN
cp = buf + off + ICMP6ECHOLEN + ICMP6ECHOTMLEN;
dp = outpack + ICMP6ECHOLEN + ICMP6ECHOTMLEN;
datap = &outpack[ICMP6ECHOLEN + ICMP6ECHOTMLEN];