 VNF instance 1 fails, traffic flow will stop. A new BGP session will be established to forwarding VNF instance 2 and traffic flow will resume after a short duration outage. The second option is a load-balanced design where the CE router will use VLANs over the single-access link and maintain two separate BGP sessions to the two forward- ing VNF instances, as depicted in Figure 3.13C. This allows a load-balanced design, allowing hit- less failover of traffic in the event of a failure of either of the two forwarding VNF instances. This option will require the customer to implement a new design that is capable of taking advantage of load-balanced traffic forwarding in the cloud. Active-standby forwarder VNF instance design has disadvantages. First, the service behavior is not exactly the same as that in a single-homed design. Customers who use static routing will not be able to take advantage of the active-standby design. Finally, active-standby design is more expensive since vPE capacity will need to be reserved for the standby forwarding VNF instance. Building the Network of the Future The control plane for an instance of the vPE needs to be kept centralized due to the need to manage routing scale. Control plane VNF needs to have 1:1 redundancy in order to avoid the fail- ure of the entire vPE, in the event of a single-server failure that causes the entire control plane to fail. Active-standby design is one way to solve this problem. Active- and standby-control plane VNF instances need to be placed on geographically separated servers inside a metro cluster. This would require the active-standby synchronization logic to work over a low-latency metro connec- tion between the active and standby control plane VNFs. Traditional router software design assumes active and standby components that exist over a backplane and therefore expect very low latency (<100 us). Metro-distance links typically have latencies in the 1-5 ms range. Hence, the control plane redundancy software logic needs to be redesigned to deal with inc