Beyond the RIB: The Label Edge

In a standard IP network, every router along a path must inspect the destination IP and search its entire Routing Information Base (RIB). In MPLS, this lookup happens only once at the Label Edge Router (LER). The LER assigns a fixed-length 'label' to the packet and forwards it into the MPLS core.

Label Distribution Protocol (LDP) Logic

How do routers agree on which label represents which destination? LDP is the signaling protocol that disseminated label mappings. A router allocates a local label for a prefix and informs its neighbors: "If you want to reach prefix X, send it to me with label Y."

The Power of Label Stacking

MPLS allows for multiple labels to be 'pushed' onto a single packet, creating a Label Stack. This is the foundation of modern VPNs.

• Outer Label (Transport): Gets the packet across the provider core to the correct egress router.
• Inner Label (Service): Identifies the specific customer VRF or pseudo-wire at the destination.

Traffic Engineering (MPLS-TE)

Unlike standard routing which always follows the 'shortest' path, MPLS-TE allows engineers to steer traffic along paths with guaranteed bandwidth or specific latency characteristics. This is achieved by combining MPLS with RSVP (Resource Reservation Protocol).

As networks transition toward Segment Routing (SR), the foundational concepts of label switching and source-based path steering continue to define the architecture of the modern high-performance internet.