The default settings for the Alcatel-Lucent 7750 SR when using LDP are ordered control mode and downstream unsolicited. In ordered control mode, LDP assigns labels to routes in a specified order, and downstream unsolicited refers to the method by which routers distribute labels to their peers without requiring a request.

In MPLS (Multiprotocol Label Switching), packets are assigned to a Forwarding Equivalence Class (FEC) at the Ingress Label Edge Router (iLER). The iLER is responsible for the initial classification and labeling of packets entering the MPLS network. Once assigned to an FEC, packets follow the same path through the network until they reach the egress point.

The MPLS (Multiprotocol Label Switching) control plane is responsible for label allocation and management as well as label signaling. Label allocation and management involve assigning labels to routes and managing those labels. Label signaling is the process by which label information is distributed between routers to establish the label-switched paths (LSPs). Label swapping, pushing a label, and routing lookups are part of the MPLS data plane, responsible for forwarding packets through the network based on labels received from the control plane.

For LDP identifiers, the last two octets are used to identify a specific label space within the Label Switch Router (LSR). When a router employs a per-platform label space, this value is always zero. This is because in a per-platform label space setup, labels are not differentiated based on interfaces but are instead managed centrally by the platform, necessitating a zero value for these octets.