Methods and techniques for flooding packets on a per-virtual-network basis are described. Some embodiments provide a method (e.g., a switch) which determines an internal virtual network identifier based on one or more fields in a packet's header. Next, the method performs a forwarding lookup operation based on the internal virtual network identifier. If the forwarding lookup operation succeeds, the method can process and forward the packet accordingly. However, if the forwarding lookup operation fails, the method can determine a set of egress ports based on the internal virtual network identifier. Next, for each egress port in the set of egress ports, the method can flood the packet if a virtual network identifier in the packet's header is associated with the egress port. Flooding packets on a per-virtual-network basis can substantially reduce the amount of resources required to flood the packet when a forwarding lookup operation fails.