Supported Platforms
How a Packet Travels Along an LSP
When an IP packet enters an LSP, the ingress router examines the packet and assigns it a label based on its destination, placing the label in the packet’s header. The label transforms the packet from one that is forwarded based on its IP routing information to one that is forwarded based on information associated with the label.
The packet is then forwarded to the next router in the LSP. This router and all subsequent routers in the LSP do not examine any of the IP routing information in the labeled packet. Rather, they use the label to look up information in their label forwarding table. They then replace the old label with a new label and forward the packet to the next router in the path.
When the packet reaches the egress router, the label is removed, and the packet again becomes a native IP packet and is again forwarded based on its IP routing information.
