+/*
+ * For IPv4-mapped IPv6 addresses, length of the prefix that precedes
+ * the 4 bytes of IPv4 address at the end of the IPv6 address.
+ */
+#define IPV4_MAPPED_HEADING_LEN 12
+
+/*
+ * Is an IPv6 address an IPv4-mapped address?
+ */
+static int
+is_ipv4_mapped_address(const u_char *addr)
+{
+ /* The value of the prefix */
+ static const u_char ipv4_mapped_heading[IPV4_MAPPED_HEADING_LEN] =
+ { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xFF, 0xFF };
+
+ return memcmp(addr, ipv4_mapped_heading, IPV4_MAPPED_HEADING_LEN) == 0;
+}
+