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Software Configuration Guide—Release IOS XE 3.3.0SG and IOS 15.1(1)SG
OL-25340-01
Chapter 11 Configuring Cisco NSF with SSO Supervisor Engine Redundancy
About NSF with SSO Supervisor Engine Redundancy
• Routing Protocols, page 11-5
• NSF Guidelines and Restrictions, page 11-9
About Cisco IOS NSF-Aware and NSF-Capable Support
Cisco IOS Nonstop Forwarding (NSF) has two primary components:
• NSF-awareness—If neighboring router devices detect that an NSF router can still forward packets
when a supervisor engine switchover happens, this capability is referred to as NSF-awareness. Cisco
IOS enhancements to the Layer 3 routing protocols (OSPF, BGP, EIGRP and IS-IS) are designed to
prevent route-flapping so that the CEF routing table does not time out or the NSF router does not
drop routes. An NSF-aware router helps to send routing protocol information to the neighboring
NSF router.
• 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.
Note NSF does not support IPv6.
Note NSF- capable devices include Catalyst 4500 series switches, Catalyst 6500 series switches, Cisco 7500
series routers, Cisco 10000 series routers, and Cisco 12000 series routers.
A typical topology for NSF and NSF-aware routers is given below.
Figure 11-1 Topology for NSF and NSF-Capable Switches
Si
Si
Si
22
Catalyst 6500 NSF
Catalyst 4500
NSF-Capable
Catalyst 4500
NSF-Capable
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