Users Guide

Table Of Contents
Dell PowerConnect ArubaOS 5.0 | User Guide OSPFv2 | 453
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
Branch Office Scenario
The branch office scenario has a number of remote branch offices with controllers talking to a central office via an
Dell 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 99). 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 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 99 Branch Office OSPF Topology
All the branch office 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 99, 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.
OSPF_001
Router 1
Router 2
Branch office
Controller 1
Branch office
Controller n
User VLAN
User VLAN
IPsec Tunnel
IPsec Tunnel
Central Office
Controller