LabelSwitched

Label-switched describes a packet-forwarding scheme in which data packets are forwarded through a network primarily by labels rather than by destination IP addresses. The most common implementation is MultiProtocol Label Switching (MPLS), where traffic is carried along pre-established Label Switched Paths (LSPs) through an MPLS domain.

In an MPLS network, edge routers known as Label Edge Routers (LERs) attach or remove labels to packets; internal routers called Label Switching Routers (LSRs) switch packets based on the top label in their label forwarding information base. A label-switched packet carries a stack of labels, and each LSR applies a label lookup to determine the next hop and the action, often swapping the top label with a new one or popping it. The egress LER removes labels before handing the packet to the final IP network. Labels are distributed using protocols such as the Label Distribution Protocol (LDP) or resource Reservation Protocol with traffic engineering extensions (RSVP-TE).

Label-switched networks enable fast forwarding and traffic engineering, support virtual private networks, and allow efficient QoS-enabled paths. They also facilitate multiprotocol support, hence "multi-protocol" in MPLS. However, they introduce management and interoperability complexity, require careful label space management, and depend on proper coordination across routing domains. Originating in the late 1990s, label-switching has become widespread in both service provider backbones and large enterprise networks.