As shown in the figure, Site1 and Site2 need to communicate through a carrier's BGP/MPLS IP VPN. A public network tunnel has been established between PE1 and PE2 (label information is shown in the figure). PE1 has advertised the 192.168.1.0/24 route of Site1 to PE2 through MP-IBGR and route learning is normal. What is the top label in a data packet transmitted on the link P -> PE1 if the packet is sent by Site2 to 192.168.1.0/24 of Site1?
The correct answer is 6662. In an MPLS network, when a packet is forwarded from PE2 to the P router towards PE1, the P router pushes the top label 6662, which is the label for the FEC 1.1.1.1/32. This label information is provided in the figure under the LDP LSP (Label Distribution Protocol Label Switched Path) section. Therefore, the top label in the data packet transmitted on the link P -> PE1 is 6662.
out label should be 3 as it is mentioned in P router as out label for 1.1.1.1/32 route
label 3 is implicit so must be poped in penultimate hop