That was a nice question.   It's very simple that every prefix in the MPLS cloud is bind to a label value which is unique to the router.    For example see the below setup   RouterA ------MPLS--------- Router B-----MPLS------Router C----IPV4---Router D. Loopback 3.3.3.3         10.0.0.1                   10.0.0.2     12.0.0.1           12.0.0.2      13.0.0.1     13.0.0.2   once I enable MPLS on all the router Router D will start assigning a label to the prefixes to which it was the reachability and directly connected its going to assign a value of 3 and will send it to Router C   Now 3.3.3.3 got a value of 3 and will be sent to Router C which will assign another label instead of 3 and will send to Router B similarly Router B will assign and send to Router A.  For 3.3.3.3 Routers          Label Assigned   Label sent              Label received D                      3                       3 sent to C                Non   C                    194                    194 sent to B               3   B                     135                   135 sent to A               194   A                                 ------------- Similar pattern---------   The thumb rule for the MPLS router is whenever they receive a label value of 3 for a prefix then it need to open the MPLS packet remove the MPLS label and send it as IPv4 packet ... View more