+/*
+ * ECN (Explicit Congestion Notification) codepoints in RFC3168
+ * mapped to the lower 2 bits of the TOS field.
+ */
+#define IPTOS_ECN_NOTECT 0x00 /* not-ECT */
+#define IPTOS_ECN_ECT1 0x01 /* ECN-capable transport (1) */
+#define IPTOS_ECN_ECT0 0x02 /* ECN-capable transport (0) */
+#define IPTOS_ECN_CE 0x03 /* congestion experienced */
+#define IPTOS_ECN_MASK 0x03 /* ECN field mask */