_s6_addr32
((a)->_s6_addr32[0] == 0 && (a)->_s6_addr32[1] == 0 && \
(a)->_s6_addr32[2] == 0 && (a)->_s6_addr32[3] == 0)
((a)->_s6_addr32[0] == 0 && (a)->_s6_addr32[1] == 0 && \
(a)->_s6_addr32[2] == 0 && (a)->_s6_addr32[3] == ntohl(1))
((a)->_s6_addr32[0] == 0 && (a)->_s6_addr32[1] == 0 && \
(a)->_s6_addr32[2] == ntohl(0x0000ffff))
((a)->_s6_addr32[0] == 0 && \
(a)->_s6_addr32[1] == 0 && \
(a)->_s6_addr32[2] == 0 && \
(a)->_s6_addr32[3] != 0 && (a)->_s6_addr32[3] != ntohl(1))