Chapter 8: Configuring High Availability Features 133
SSO switchover also preserves FIB and adjacency entries and can forward Layer 3 traffic
after a switchover. Configuration information and data structures are synchronized from
the active to the redundant Supervisor engine at startup and whenever changes to the
active Supervisor engine configuration occur. Following an initial synchronization
between the two Supervisor engines, SSO maintains state information between them,
including forwarding information.
During switchover, system control and routing protocol execution is transferred from the
active Supervisor engine to the redundant Supervisor engine. The switch requires
between 0 and 3 seconds to switchover from the active to the redundant Supervisor
engine.
Cisco NSF always runs with SSO and provides redundancy for Layer 3 traffic. NSF works
with SSO to minimize the amount of time that a network is unavailable to its users fol-
lowing a switchover. The main purpose of NSF is to continue forwarding IP packets fol-
lowing a Supervisor engine switchover
The following events cause a switchover:
â– A hardware failure on the active Supervisor engine
â– Clock synchronization failure between Supervisor engines
â– A manual switchover
SSO/NSF Configuration
1. Enter redundancy configuration mode:
(global) redundancy
From Global configuration mode, enter the command redundancy to move into
redundancy configuration mode.
2. Select SSO redundancy mode.
(redundancy) mode sso
This enables redundant supervisor modules to run in SSO mode. This mode enables
the support of NSF for applicable protocols.
3. Save configuration:
(exec) copy running-config startup-config
After you configure SSO, you need to save the configuration.
4. (Optional) Configuring Multicast MLS NSF with SSO.
Multicast MLS NSF with SSO is on by default when you select SSO as the redun-
dancy mode:
a. (Optional) Configure MLS wait time:
(global) mls ip multicast sso convergence-time time
Section 8-2
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