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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
Codes: C - connected, O - OSPF, R - RIP, S - static
M - mgmt, U - route usable, * - candidate default
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 Office Scenario
The branch office scenario has a number of remote branch offices with Dell controllers talking to a central office via
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 41). 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 Office Topology
All the OSPF control packets exchanged between the Branch office and the Central office Dell controllers undergo
GRE encapsulation before entering the IPsec tunnels. The Dell 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 41: Branch Office OSPF Topology
All the branch office Dell controllers, the Central office controller, and the upstream routers are part of a stub area.
Since 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 interoperate with
other vendors seamlessly.
In Figure 41, the branch office controller is configured using VLAN 14 and VLAN 15. Layer 3 GRE tunnel is
configured with IP address 20.1.1.1/24 and OSPF is enabled on the tunnel interface.
In the Central office controller, OSPF is enabled on VLAN interfaces 4, 5, and, the Layer 3 GRE tunnel interface
(configured with IP address 20.1.1.2/24). OSPF interface cost on VLAN 4 is configured lower than VLAN 5.
DellPowerConnectW-SeriesArubaOS6.2 | User Guide OSPFv2 | 154