Figure 1 shows a four router topology. R1 is connected to R2. R2 is connected to R3. R3 is connected to R4. Each router has a LAN. The LANs are assign /27 subnets and the WAN links between the routers are assigned /30 subnets. Figure 2 shows the configuration commands to configure the interfaces on R1 for building A. Figure 3 shows the configuration commands to configure the interfaces on R2 for building B. Figure 4 shows the configuration commands to configure the interfaces on R3 for building C. Figure 5 shows the configuration commands to configure the interfaces on R4 for building D.