What does a PE do when a frame is received in a VPLS service with an unknown destination address by default?

Virtual Private LAN Service (VPLS) is designed to emulate an Ethernet LAN segment over a packet-switched network. A core function of a Layer 2 Ethernet switch is to flood frames with an unknown destination MAC address to all ports within the broadcast domain (except the ingress port). By default, a Provider Edge (PE) router in a VPLS service mimics this behavior. When it receives a frame for a destination MAC address not present in its Forwarding Information Base (FIB), it floods the frame to all other PEs in the service via Service Distribution Path (SDP) tunnels and to all local Service Access Points (SAPs).

A. Dropping the frame would prevent communication from being established with new or silent hosts, breaking the fundamental learning-bridge behavior that VPLS emulates.
C. Sending a "destination unreachable" message is a Layer 3 (IP/ICMP) function. VPLS operates at Layer 2 and is unaware of IP-level constructs.
D. Storing frames until the destination is known is not a standard mechanism in Ethernet switching or VPLS; it would introduce unacceptable latency and complexity.

1. Nokia 7750 SR OS, 7450 ESS, and 7950 XRS VPLS, PBB, and EVPN Services Guide, Release 22.10.R1, Document Part Number: 3HE-18301-AAAB-TQZZA, Section: VPLS Service Overview. "Unknown unicast frames and broadcast frames are flooded to all SAPs and SDPs that are part of the VPLS service."

2. Nokia 4A0-104 Courseware, Module 3: Virtual Private LAN Services. The module explains that unknown unicast MAC addresses, along with broadcast and multicast frames, are flooded throughout the VPLS instance.