6-2
Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 6 Configuring Supervisor Engine Redundancy Using RPR and SSO
Understanding Cisco IOS NSF-Awareness Support
Understanding Cisco IOS NSF-Awareness Support
Cisco IOS Nonstop Forwarding (NSF) has two primary components:
NSF-capability—NSF works with SSO to minimize the amount of time that a Layer 3 network is
unavailable following a supervisor engine switchover by continuing to forward IP packets.
Reconvergence of Layer 3 routing protocols (BGP, EIGRP, OSPF v2, and IS-IS) is transparent to the
user and happens automatically in the background. The routing protocols recover routing
information from neighbor devices and rebuild the Cisco Express Forwarding (CEF) table.
NSF-awareness—If neighboring router devices detect that an NSF router can still forward packets
when RP (Route Processor) switchover happens, this capability is referred to as NSF-awareness.
Cisco IOS enhancements to the Layer 3 protocols OSPF, BGP, EIGRP and IS-IS are designed to
prevent route-flapping so that the CEF routing table does not timeout or the NSF router does not
drop routes. An NSF-aware router helps to send routing protocol information to the neighboring
NSF router.
Note NSF capable devices are Catalyst 6500 series switches, Cisco 7500 series routers, Cisco 10000 series
routers, and Cisco 12000 series routers. The Catalyst 4500 series switch is an NSF-aware device for
Release 12.2(20)EWA.
For more information on BGP, EIGRP, OSPF, and IS-IS NSF-awareness, refer to the URL:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1839/products_feature_guides_list.html
A typical topology for NSF and NSF-aware routers is given below.
Figure 6-1 Topology for NSF and NSF-Aware Router
Si
Si
Si
22
Catalyst 6500 NSF
Catalyst 4500
NSF-Aware
Catalyst 4500
NSF-Aware
120103
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