``packet_in'' message will be sent only to the controllers having
controller id zero which have registered for the invalid ttl packets.
.
+.IP \fBset_mpls_ttl\fR:\fIttl\fR
+Set the TTL of the outer MPLS label stack entry of a packet.
+\fIttl\fR should be in the range 0 to 255 inclusive.
+.
.IP \fBdec_mpls_ttl\fR
Decrement TTL of the outer MPLS label stack entry of a packet. If the TTL
is initially zero, no decrement occurs. Instead, a ``packet-in'' message