ink for the purpose of high availability is expensive; customers choose dual-homed access only for larger locations with high uptime requirement. Blast radius is an informal term used to describe the extent of impact of a failure event. Network design attempts to keep blast radius small SO that a failure event impacts the smallest possible number of users. Network Functions Virtualization Forwarding Instance 1 BGP Session-1 Ethernet Load-balanced Router Fabric BGP Session-2 Forwarding Instance 2 A. Dual-homed Customer Site with two BGP session for each link Forwarding Instance 1 Ethernet Active-Standby Router Fabric Forwarding Instance 2 B. Single-homed Customer Site with one BGP session to the network Forwarding Instance 1 Ethernet Load-balanced Router Fabric Forwarding Instance 2 C. Single-homed Customer Site with two BGP sessions to the network FIGURE 3.13 (A, B, and C): Distributed forwarding VNF instances. Figure 3.13 shows three different design options for distributing forwarding plane functions over multiple instances of forwarding VNFs. Using multiple instances of forwarding VNF is straightforward for a customer who has dual- homed access links. Each access link will connect to a separate instance of the forwarding VNF. BGP sessions will be established between customer router and each of the VNF instances, enabling a load-balanced design. If forwarding VNF instance 1 fails, traffic will migrate in a hitless manner, to forwarding VNF instance 2. This is depicted in Figure 3.13A. Using multiple forwarding instances is more difficult in the case of a customer who has only a single-access link to the network. There are two design choices as depicted in Figure 3.13B and C. The first option is an active-standby design for the two forwarding VNF instances. The network cloud data center fabric will terminate the access line and manage two connections, one each to each of the two instances of forwarding VNFs. There will be only one BGP session between the CE router and forwarding VNF instance 1. If the forwarding