Cisco Systems 3750E manual Ospf NSF Awareness, 38-28

Chapter 38 Configuring IP Unicast Routing

Configuring OSPF

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 Catalyst 3750-E 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.

When the neighbor relationships are reestablished, the NSF-capable stack master resynchronizes its database with its NSF-aware neighbors, and routing information is exchanged between the OSPF neighbors. The new stack master uses this routing information to remove stale routes, to update the routing information database (RIB), and to update the forwarding information base (FIB) with the new information. The OSPF protocols then fully converge.

Note OSPF NSF requires that all neighbor networking devices be NSF-aware. If an NSF-capable router discovers non-NSF aware neighbors on a network segment, it disables NSF capabilities for that segment. Other network segments where all devices are NSF-aware or NSF-capable continue to provide NSF capabilities.

Use the nsf OSPF routing configuration command to enable OSPF NSF routing. Use the show ip ospf privileged EXEC command to verify that it is enabled.

For more information about this feature, see the Cisco Nonstop Forwarding Feature Overview at this URL: http://www.cisco.com/en/US/products/sw/iosswrel/ps1829/products_feature_guide09186a00800ab7fc. html

Note NSF is not supported on interfaces configured for Hot Standby Router Protocol (HSRP).

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
38-28	OL-9775-02