Cisco Catalyst 4500 series Administration Manual page 455

Chapter 11 Configuring Supervisor Engine Redundancy Using RPR and SSO on Supervisor Engine 7-E, Supervisor
RPR Operation
RPR is supported in Cisco IOS-XE Release 3.1.0SG and later releases. When a standby supervisor
engine runs in RPR mode, it starts up in a partially-initialized state and is synchronized with the
persistent configuration of the active supervisor engine.
Note Persistent configuration includes the following components: startup-config, boot variables,
config-register, and VLAN database.
The standby supervisor engine pauses the startup sequence after basic system initialization, and in the
event that the active supervisor engine fails, the standby supervisor engine becomes the new active
supervisor engine.
In a supervisor engine switchover, traffic is disrupted because in the RPR mode all of the physical ports
restart since there is no state maintained between supervisor engines relating to module types and
statuses. Upon switchover, when the standby supervisor engine completes its initialization, it will read
hardware information directly from the module and become the active supervisor engine.
SSO Operation
SSO is supported in Cisco IOS-XE Release 3.1.0SG and later releases. When a standby supervisor
engine runs in SSO mode, the standby supervisor engine starts up in a fully-initialized state and
synchronizes with the persistent configuration and the running configuration of the active supervisor
engine. It subsequently maintains the state on the protocols listed below, and all changes in hardware
and software states for features that support stateful switchover are kept in synchronization.
Consequently, it offers zero interruption to Layer 2 sessions in a redundant supervisor engine
configuration.
Because the standby supervisor engine recognizes the hardware link status of every link, ports that were
active before the switchover will remain active, including the uplink ports. However, because uplink
ports are physically on the supervisor engine, they will be disconnected if the supervisor engine is
removed.
If the active supervisor engine fails, the standby supervisor engine become active. This newly active
supervisor engine uses existing Layer 2 switching information to continue forwarding traffic. Layer 3
forwarding will be delayed until the routing tables have been repopulated in the newly active supervisor
engine.
SSO supports stateful switchover of the following Layer 2 features.
Note
The state of these features is preserved between both the active and standby supervisor engines:
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OL_28731-01
SSO is not supported if the IOS-XE software is running in the LAN Base mode.
802.3
802.3u
802.3x (Flow Control)
802.3ab (GE)
802.3z (Gigabit Ethernet including CWDM)
802.3ad (LACP)
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
About Supervisor Engine Redundancy
11-3