42-28
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 42 Configuring IP Unicast Routing
Configuring OSPF
OSPF Nonstop Forwarding
The switch or switch stack supports two levels of nonstop forwarding (NSF):
• OSPF NSF Awareness, page 42-28
• OSPF NSF Capability, page 42-28

OSPF NSF Awareness

The IP-services feature set supports OSPF NSF Awareness supported for IPv4. When the neighboring
router is NSF-capable, the Layer 3 switch continues to forward packets from the neighboring router
during the interval between the primary Route Processor (RP) in a router crashing and the backup RP
taking over, or while the primary RP is manually reloaded for a non-disruptive software upgrade.
This feature cannot be disabled. For more information on this feature, see the “OSPF Nonstop
Forwarding (NSF) Awareness” section of the Cisco IOS IP Routing Protocols Configuration Guide,
Release 12.4 at this URL:
http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a00804557
a8.html

OSPF NSF Capability

The IP-services feature set also 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.
After a stack master change, the new master sends an OSPF NSF signal to neighboring NSF-aware
devices. A device recognizes this signal to mean that it should not reset the neighbor relationship with
the stack. As the NSF-capable stack master receives signals from other routes on the network, it begins
to rebuild its neighbor list.
Timers shortest path first (spf) spf delay: 5 seconds.; spf-holdtime: 10 seconds.
Virtual link No area ID or router ID defined.
Hello interval: 10 seconds.
Retransmit interval: 5 seconds.
Transmit delay: 1 second.
Dead interval: 40 seconds.
Authentication key: no key predefined.
Message-digest key (MD5): no key predefined.
1. NSF = Nonstop forwarding
2. OSPF NSF awareness is enabled for IPv4 on Catalyst 3750-E and 3560-E switches running the IP services feature set.
Table 42-5 Default OSPF Configuration (continued)
Feature Default Setting