Users Guide

Codes: C - connected, O - OSPF, R - RIP, S - static
M - mgmt, U - route usable, * - candidate default
Below is the routing table for Router 1:
(router1) #show ip route
O 10.1.1.0/24 [1/0] via 4.1.1.1
O 12.1.1.0/24 [1/0] via 4.1.1.1
C 4.1.1.0 is directly connected, VLAN4
Below is the routing table for Router 2:
(router2) #show ip route
O 10.1.1.0/24 [2/0] via 5.1.1.1
O 12.1.1.0/24 [2/0] via 5.1.1.1
C 5.1.1.0 is directly connected, VLAN5
Understanding OSPFv2 by Example using a Branch Scenario
The branch office scenario has a number of remote branch offices with controllers talking to a central office via
a concentrator/controller using site-to-site VPN tunnels or master-local IPsec tunnels. The central office
controller is in turn talking to upstream routers (see Figure 35). In this scenario, the default route is normally
pointed to the uplink router, in many cases the ISP. Configure the area as stub so that inter-area routes are also
advertised enabling the branch office controller to reach the corporate subnets.
Branch Topology
All the OSPF control packets exchanged between the Branch and the central office controllers undergo GRE
encapsulation before entering the IPsec tunnels. The controllers in the branch offices advertise all the user
subnet addresses to the Central office controller as stub addresses in router LSA. The central office controller in
turn forwards those router LSAs to the upstream routers.
Figure 35 Branch OSPF Topology
All the branch office controllers, the Central office controller, and the upstream routers are part of a stub area.
Because the OSPF packets follow GRE encapsulation over IPsec tunnels, the Central office controller can be a
controller or any vendor’s VPN concentrator. Regardless, the controller in the branch office will operate with
other vendors seamlessly.
Dell Networking W-Series ArubaOS 6.4.x | User Guide OSPFv2 | 231