A Virtual Private LAN Service (VPLS) requires Provider Edge (PE) routers to emulate the functions of a traditional Layer 2 Ethernet switch. The three fundamental functions are:

1. MAC Learning (A): The PE router learns the source MAC addresses of frames arriving from both customer-facing ports (SAPs) and network-facing tunnels (SDPs), populating a Forwarding Database (FDB).

2. Frame Replication (B): For frames with an unknown destination MAC address, as well as for broadcast and multicast frames (BUM traffic), the PE router must replicate and flood the frame to all other SAPs and SDPs within that VPLS instance.

3. Frame Forwarding (D): When a frame with a known destination MAC address is received, the PE router performs a lookup in its FDB and forwards the frame directly to the specific SAP or SDP associated with that MAC address.

C. Frame fragmentation: This is a Layer 3 (IP) function. VPLS operates at Layer 2; Ethernet frames are not fragmented. If a frame exceeds the transport MTU, it is dropped.

E. Must discard frames with an unknown destination MAC: This is incorrect. A VPLS PE, like a switch, must flood (replicate) frames with unknown destination MACs to enable MAC learning and communication across the emulated LAN.

F. MSTP: While a VPLS can transparently tunnel customer MSTP BPDUs, the PE router itself does not participate in the customer's Spanning Tree Protocol. The VPLS core uses split-horizon rules on SDPs to prevent loops.

1. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VPLS Service" Chapter, Section: "Learning and Forwarding": "The 7750 SR OS VPLS service is designed to emulate an Ethernet LAN segment over an IP/MPLS core... This emulation requires the 7750 SR OS to perform MAC address learning, flooding of unknown unicast, broadcast, and multicast frames, and forwarding of unicast frames to known MAC addresses." (Confirms A, B, D; refutes E).

2. RFC 4762: Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling, Section 5: "Packet Forwarding": "When a PE router receives an Ethernet frame from a CE device, it must first learn the source MAC address... If the destination MAC address is a broadcast or multicast address, or if the destination MAC address has not yet been learned by the PE, the PE MUST flood the frame... if the destination MAC address has been learned, the PE forwards the frame to the appropriate destination." (Confirms A, B, D; refutes E).

3. Nokia 7750 SR OS Services Guide, Release 21.10.R1, "VPLS Service" Chapter, Section: "Spanning Tree Protocol": "The VPLS service is transparent to the customer’s STP BPDUs... The PE does not participate in the customer’s STP topology." (Refutes F).