What triggers an ISP MPLS router to check if the packet received from the client is in the Label table to forward it via Layer 2 mpls instead of Layer 3 routing?
For example if there is a client that is advertising its subnet via BGP and has MPLS with the same ISP, once it sends a request from clientA to clientB over the mpls cloud.
Does every MPLS router check the packet for mpls labels regardless if it is suppose to forward MPLS or not?
Can you correct me if I wrong? MPLS adds an entry to the CEF FIB so that when the router does a lookup, it sees that the fib has an mpls label and then checks the LIB and later LFIB table?
Packets received from customers are generally received as IP packets. The FIB will either contain a label (or label stack) or not. This is generally where the decision is made to label switch or not.