-Sets the IPv4 ToS/DSCP field to \fItos\fR. Valid values are between 0 and
-255, inclusive. Note that the two lower reserved bits are never
-modified.
+Sets the IPv4 ToS/DSCP field to \fItos\fR, which must be a multiple of
+4 between 0 and 255. This action does not modify the two least
+significant bits of the ToS field (the ECN bits).