162| OSPFv2 AOS-W 6.5.3.x| User Guide
n In the WLAN scenario, configure the Alcatel-Lucent switch and all upstream routers in totally stub area; in
the Branch scenario, configure as stub area so that the Branch switch can receive corporate subnets.
n In the WLAN scenario upstream router, only configure the interface connected to the switch in the same
area as the switch. This will minimize the number of local subnet addresses advertised by the upstream
router to the switch.
n Use the upstream router as the designated router (DR) for the link/interface between the switch and the
upstream router.
n The default MTU value for a Layer 3 GRE tunnel in an Alcatel-Lucent switch is 1100. When running OSPF
over a GRE tunnel between an Alcatel-Lucent switch and another vendor’s router, the MTU values must be
the same on both sides of the GRE tunnel.
n Do not enable OSPF on any uplink/WAN interfaces on the Branch Switch. Enable OSPF only on the Layer 3
GRE tunnel connecting the master switch.
n Use only one physical port in the uplink VLAN interface that is connecting to the upstream router. This will
prevent broadcasting the protocol PDUs to other ports and hence limit the number of adjacencies on the
uplink interface to only one.
Understanding OSPFv2 by Example using a WLAN Scenario
In the WLAN scenario, the Alcatel-Lucent switch acts as a default gateway for all the clients, and talks to one or
two upstream routers for redundancy. The switch advertises all the user subnet addresses as stub addresses to
the routers via LSAs.
Totally stub areas see only default route and to the areas themselves.
WLAN Topology
The switch (Figure 29) is configured with VLAN 10 and VLAN 12 as user VLANs. These VLANs have clients on the
subnets, and the switch is the default router for those clients. VLAN 4 and VLAN 5 both have OSPF enabled.
These interfaces are connected to upstream routers (Router 1 and Router 2). The OSPF interface cost on VLAN
4 is configured lower than VLAN 5. The IDs are:
n Alcatel-Lucent switch— 40.1.1.1
n Router 1— 50.1.1.1
n Router 2— 60.1.1.1
Figure 29 WLAN OSPF Topology
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