+/* The IPv6 flow label is in the lower 20 bits of the first 32-bit word. */
+#define IPV6_LABEL_MASK 0x000fffff
+
+/* Example:
+ *
+ * char *string = "1 ::1 2";
+ * char ipv6_s[IPV6_SCAN_LEN + 1];
+ * struct in6_addr ipv6;
+ *
+ * if (sscanf(string, "%d"IPV6_SCAN_FMT"%d", &a, ipv6_s, &b) == 3
+ * && inet_pton(AF_INET6, ipv6_s, &ipv6) == 1) {
+ * ...
+ * }
+ */
+#define IPV6_SCAN_FMT "%46[0123456789abcdefABCDEF:.]"
+#define IPV6_SCAN_LEN 46
+