Nsf Overview - Cisco Catalyst 4500 Series Software Configuration Manual

Chapter 7 Configuring the Cisco IOS In-Service Software Upgrade Process
Figure 7-2
Service provider
access layer

NSF Overview

Cisco NSF works with the SSO feature in Cisco IOS software. SSO is a prerequisite of Cisco NSF. NSF
works with SSO to minimize the amount of time a network is unavailable to its users following a
switchover. The main objective of Cisco NSF is to continue forwarding IP packets following a supervisor
engine switchover.
Usually, when a networking device restarts, all routing peers of that device detect that the device went
down and then came back up. This transition results in what is called a routing flap, which could spread
across multiple routing domains. Routing flaps caused by routing restarts create routing instabilities,
which are detrimental to the overall network performance. Cisco NSF helps to suppress routing flaps in
SSO-enabled devices, thus reducing network instability.
Cisco NSF allows for the forwarding of data packets to continue along known routes while the routing
protocol information is being restored following a switchover. With Cisco NSF, peer networking devices
do not experience routing flaps. Data traffic is forwarded while the standby supervisor engine assumes
control from the failed active supervisor engine during a switchover. The ability of physical links to
remain up through a switchover and to be kept current with the Forwarding Information Base (FIB) on
the active supervisor engine is key to Cisco NSF operation.
Cisco NSF with SSO Network Deployment: Enterprise Networks
Service
provider
core
layer
distribution
layer
Service
provider
Enterprise
access
layer
Enterprise
distribution
layer
Enterprise
core
layer
Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.0E and IOS 15.2(5)E
About ISSU
Cisco NSF with SSO
features may provide
some benefit, but usually
not required
Good position for
NSF-aware
routers
Primary deployment
position for Cisco NSF
with SSO-capable routers
Secondary deployment
position for Cisco NSF
with SSO-capable
or -aware routers
Good position for
NSF-aware
routers
SSO may provide
some benefit
7-5