Why does Junos create two entries in LIB for single tag- one with "S=0" and other with implicit "S=1"?

Question

In the penultimate LSR there are following two entries for label 301040:

root@r2> show route table mpls.0 protocol rsvp

mpls.0: 14 destinations, 14 routes (14 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

301040             *[RSVP/7/1] 00:06:53, metric 1
                    > to 172.22.201.14 via ge-0/0/2.0, label-switched-path r1->r4
301040(S=0)        *[RSVP/7/1] 00:06:53, metric 1
                    > to 172.22.201.14 via ge-0/0/2.0, label-switched-path r1->r4

root@r2>

Am I correct, that one should look the S=0 as a condition, i.e if the S=0(bottom of stack bit in MPLS header is not set) then do something and this something can be different when the S=1(bottom of stack bit in MPLS header is set)? For example, LSR could swap the label 301040 with label 12345 if it is at the bottom of the stack or pop the label 301040 if it is not at the bottom of the stack.

Answer 1

S=0 means that the label is not at the bottom at the stack. In some situations, a packet may contain more than 1 label, and each of these labels serves a different purpose. In this case, we can force the router to process such a packet differently than a packet with only one label. Please refer to this(label stacking section): https://www.juniper.net/documentation/en_US/junos/topics/reference/command-summary/show-route-table.html