_T_OPTHDR_SZ
((nbp)->len >= _T_OPTHDR_SZ ? (struct t_opthdr *)(nbp)->buf : \
((unsigned char *)_T_OPTDATA_ALIGN((char *)(tohp) + _T_OPTHDR_SZ))
_T_OPTHDR_SZ <= ((char *)(pbuf) + (buflen))) ? \
