What is MPLS?
Answer
MPLS (Multiprotocol Label Switching) is a routing technique that uses short labels attached to packets to make forwarding decisions, rather than examining the full IP header at each hop. This makes forwarding faster and allows for traffic engineering. How it works: at the ingress MPLS router (LER — Label Edge Router), a label is pushed onto the packet. Intermediate routers (LSRs — Label Switch Routers) forward based solely on the label (swap the label with the next label). At the egress LER, the label is popped and the packet is forwarded normally. MPLS creates LSPs (Label Switched Paths) — predetermined paths through the network. Benefits: traffic engineering (control paths explicitly), QoS (label-based forwarding with different treatment), VPNs (MPLS VPNs separate customer traffic using labels), and faster forwarding. Widely used by ISPs and for enterprise MPLS WAN services. Being replaced by SD-WAN in many deployments.