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38-28
Catalyst 3750 Switch Software Configuration Guide
OL-8550-09
Chapter 38 Configuring IP Unicast Routing
Configuring OSPF
OSPF for Routed Access
With Cisco IOS Release 12.2(55)SE, the IP Base image supports OSPF for routed access. The IP services
image is required if you need multiple OSPFv2 and OSPFv3 instances without route restrictions.
Additionally, the IP services image is required to enable the multi-VRF-CE feature.
OSPF for Routed Access is specifically designed so that you can extend Layer 3 routing capabilities to
the wiring closet.
Note OSPF for Routed Access supports only one OSPFv2 and one OSPFv3 instance with a combined total of
200 dynamically learned routes. The IP Base image provides OSPF for routed access.
However, these restrictions are not enforced in this release.
With the typical topology (hub and spoke) in a campus environment, where the wiring closets (spokes)
are connected to the distribution switch (hub) that forwards all nonlocal traffic to the distribution layer,
the wiring closet switch need not hold a complete routing table. A best practice design, where the
distribution switch sends a default route to the wiring closet switch to reach interarea and external routes
(OSPF stub or totally stub area configuration) should be used when OSPF for Routed Access is used in
the wiring closet.
For more details, go to:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Campus/routed-ex.html
OSPF Nonstop Forwarding
The switch stack supports two levels of nonstop forwarding (NSF):
• OSPF NSF Awareness, page 38-28
• OSPF NSF Capability, page 38-28
OSPF NSF Awareness
The IP services image supports OSPF NSF Awareness for IPv4. When a neighboring router is
NSF-capable, the Layer 3 switch continues to forward packets from the router before the backup Route
Processor (RP) in a router takes over after the primary RP fails, or while the primary RP is manually
reloaded for a nondisruptive software upgrade.
This feature cannot be disabled. For more information on this feature, see the OSPF Nonstop Forwarding
(NSF) Awareness Feature Guide:
http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ftosnsfa.html
OSPF NSF Capability
The IP services image supports OSPF NSF-capable routing for IPv4 for better convergence and lower
traffic loss following a stack master change. When a stack master change occurs in an OSPF
NSF-capable stack, the new stack master must do two things to resynchronize its link-state database with
its OSFP neighbors:
• Release the available OSPF neighbors on the network without resetting the neighbor relationship.
• Reacquire the contents of the link-state database for the network.