At the edge of the MPLS network, a router needs to label the IP packets. A stack of at least one label is imposed on the IP packet on the ingress LSR. The imposed label stack is not limited by the number of labels, so the IP packet can receive one, two, three, or more labels at the ingress PE router. When you look at the CEF table on the ingress PE router, you can see for each prefix what the imposed label stack is. Example 6-10 shows an example of labeling the packets that are destined for the prefix 10.200.254.4/32 with one label.
london#show ip cef 10.200.254.4 detail 10.200.254.4/32, epoch 5 local label info: global/21 nexthop 10.200.200.2 Ethernet0/0/0 label 23