VPLS (Virtual Private LAN Service) is a Layer 2 VPN technology that simulates a LAN across an MPLS or IP core. VPLS uses a flood-and-learn mechanism where unknown unicast, broadcast, and multicast traffic is flooded to build the forwarding database dynamically - much like a traditional LAN switch.
* This flood-and-learn behavior leads to MAC learning based on incoming traffic, not control-plane advertisement.
* VPLS may require extra control-plane scaling mechanisms in large-scale deployments due to this learning behavior.
Other options explained:
* A (LISP): Uses mapping servers and control plane for EID-to-RLOC mapping, not flood-and-learn.
* B (OTV): Uses control-plane MAC address learning instead of data-plane flooding.
* D (EVPN): Uses BGP control-plane learning for MAC and IP address distribution.
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* A: The overload bit (OL bit) signals other routers to avoid using the overloaded router as a transit path for Level 2 traffic. However, the overloaded router can still forward Level 1 local area traffic if applicable.
* D: The overload bit is commonly used during router bootup to prevent temporary black holes while the router completes its routing protocol convergence and LSDB synchronization.
Why other options are incorrect:
* B: CSNP prioritization is not related to overload bit functionality.
* C: LSDB synchronization occurs through normal IS-IS mechanisms; overload bit is not involved.
* E: The overload bit prevents transit usage, not attracts traffic.