Users Guide

Table Of Contents
Dell PowerConnect ArubaOS 5.0 | User Guide] OSPFv2 | 451
Chapter 23
OSPFv2
OSPFv2 (Open Shortest Path First) is a dynamic Interior Gateway routing Protocol (IGP) based on IETF RFC
2328. The premise of OSPF is that the shortest or fastest routing path is used. Dell’s implementation of OSPFv2
allows Dell controllers to be deployed effectively in a Layer 3 topology. Dell controllers can act as default gateway
for all clients and forward user packets to the upstream router. The information in this chapter is in the following
sections:
z “Important Points to Remember” on page451
z “WLAN Scenario” on page451
z “Branch Office Scenario” on page453
z “Configuring OSPF” on page455
z “Deployment Best Practices” on page456
z “Sample Topology and Configuration” on page457
Important Points to Remember
z OSPF is disabled by default
z Dell controllers support only one OSPF instance
z Maximum OSPF routes is 1K
z Convergence takes between 5 and 15 seconds
z Only stub and totally stub areas are supported
z Only one area can be configured
z An Dell controller can not act as ABR (Area border router) or ASBR (Autonomous system border router)
z OSPF packets use generic routing encapsulation (GRE) over Internet Protocol Security (IPsec) tunnels. A
Layer 3 GRE tunnel is configured between two routers with GRE destination addresses as the inner address of
the IPsec tunnel. OSPF is enabled on the Layer 3 GRE tunnel interface and all of the OSPF control packets
undergo GRE encapsulation before entering the IPsec tunnels.
z The default MTU value for a Layer 3 GRE tunnel in an Dell controller is 1100. When running OSPF over a
GRE tunnel between an Dell controller and another vendor’s router, the MTU values must be the same on
both sides of the GRE tunnel.
OSPF is a robust routing protocol addressing various link types and deployment scenarios, the Dell
implementation applies to two main use cases; WLAN Scenario and Branch Office Scenario.
WLAN Scenario
In the WLAN scenario, the Dell controller acts as a default gateway for all the clients and talks to one or two (for
redundancy) upstream routers. The controller advertises all the user subnet addresses as stub addresses via LSAs
to the routers. The controller and upstream routers are part of a totally stub area (TSA). The upstream routers
advertise only the default route to the controller.
Note: Totally stub areas see only a default route and routes local to the areas themselves.