Section 2.0: Routing Configuration
Configure OSPF areas as shown in the Routing Protocol Information diagram in Figure 2-3 with MD5 authentication.
OSPF redundancy is a tricky question; the pointers that follow advise you on what you need to do. See Example 2-3.
You need to configure HSRP in VLAN_4 on R2 and R3. R1 should form OSPF adjacency to the HSRP Virtual IP address. See Section 9.4 for more details.
Configure GRE Tunnel on R1, R2, and R3 with any subnet not used thus far (such as 22.214.171.124/24). Make sure you change the OSPF network type to point-to-multipoint, as by default tunnel interface is point-to-point. Tunnel source should be Loopback1 on R1 and HSRP Virtual IP on R2 and R3.
Advertise the tunnel network 126.96.36.199 in OSPF ...