Catalyst 4500 Series Switch Software Configuration Guide, IOS XE 3.9.xE and IOS 15.2(5)Ex

Overview

With supervisor engine redundancy enabled, if the active supervisor engine fails or if a manual switchover is performed, the redundant supervisor engine becomes the active supervisor engine. The redundant supervisor engine has been automatically initialized with the startup configuration of the active supervisor engine, shortening the switchover time (30 seconds or longer in RPR mode, depending on the configuration; subsecond in SSO mode).

In addition to the reduced switchover time, supervisor engine redundancy supports the following:

• Online insertion and removal (OIR) of the redundant supervisor engine.

Supervisor engine redundancy allows OIR of the redundant supervisor engine for maintenance. When the redundant supervisor engine is inserted, the active supervisor engine detects its presence, and the redundant supervisor engine boots into a partially-initialized state in RPR mode and a fully-initialized state in SSO mode.

• Software upgrade. See the “Performing a Software Upgrade” section.

To minimize down time during software changes on the supervisor engine, load the new image on the redundant supervisor engine, and conduct a switchover.

When power is first applied to a switch, the supervisor engine that boots first becomes the active supervisor engine and remains active until a switchover occurs.

A switchover occurs when one or more of the following events take place:

• The active supervisor engine fails (due to either hardware or software function) or is removed.
• A user forces a switchover.
• A user reloads the active supervisor engine.

RPR Operation

RPR is supported in Cisco IOS Release 12.2(12c)EW and later releases. When a redundant 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 redundant supervisor engine pauses the startup sequence after basic system initialization, and in the event that the active supervisor engine fails, the redundant 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. When the redundant supervisor engine completes its initialization, it reads hardware information directly from the module.

SSO Operation

SSO is supported in Cisco IOS Release 12.2(20)EWA and later releases. When a redundant supervisor engine runs in SSO mode, the redundant 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 redundant supervisor engine recognizes the hardware link status of every link, ports that were active before the switchover 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 redundant supervisor engine become active. This newly active supervisor engine uses existing Layer 2 switching information to continue forwarding traffic. Layer 3 forwarding is delayed until the routing tables have been repopulated in the newly active supervisor engine.

SSO supports stateful switchover of the following Layer 2 features. The state of these features is preserved between both the active and redundant supervisor engines:

• 802.3
• 802.3u
• 802.3x (Flow Control)
• 802.3ab (GE)
• 802.3z (Gigabit Ethernet including CWDM)
• 802.3ad (LACP)
• 802.1p (Layer 2 QoS)
• 802.1q
• 802.1X (Authentication)
• 802.1D (Spanning Tree Protocol)
• 802.3af (Inline power)
• PAgP
• VTP
• Dynamic ARP Inspection
• DHCP snooping
• IP source guard
• IGMP snooping (versions 1 and 2)
• DTP (802.1q and ISL)
• MST
• PVST+
• Rapid-PVST
• PortFast/UplinkFast/BackboneFast
• BPDU guard and filtering
• Voice VLAN
• Port security
• Unicast MAC filtering
• ACL (VACLS, PACLS, RACLS)
• QoS (DBL)
• Multicast storm control/broadcast storm control

SSO is compatible with the following list of features. However, the protocol database for these features is not synchronized between the redundant and active supervisor engines:

• 802.1Q tunneling with Layer 2 Protocol Tunneling (L2PT)
• Baby giants
• Jumbo frame support
• CDP
• Flood blocking
• UDLD
• SPAN/RSPAN
• NetFlow

The following features are learned on the redundant supervisor engine if the SSO feature is enabled:

• All Layer 3 protocols on Catalyst 4500 series switches (Switch Virtual Interfaces)

RPR Supervisor Engine Configuration Synchronization

Because the redundant supervisor engine is only partially initialized in RPR mode, it interacts with the active supervisor engine only to receive configuration changes at startup and upon saving the configuration changes.

When a redundant supervisor engine is running in RPR mode, the following events trigger synchronization of the configuration information:

• When the redundant supervisor engine boots, the auto-sync command synchronizes the persistent configuration. This command is enabled by default. For details, refer to “Synchronizing the Supervisor Engine Configurations” section.
• When the active supervisor engine detects the redundant supervisor engine, the configuration information is synchronized from the active supervisor engine to the redundant supervisor engine. This synchronization overwrites any existing startup configuration file on the redundant supervisor engine.
• When you make changes to the configuration, you must use the write command to save and synchronize the startup configuration of the redundant supervisor engine.

SSO Supervisor Engine Configuration Synchronization

When a redundant supervisor engine runs in SSO mode, the following events trigger synchronization of the configuration information:

• When the active supervisor detects the redundant supervisor engine, synchronization of the persistent and running configuration takes place, allowing the redundant supervisor engine to arrive at a fully-initiated state.
• When real-time changes occur, the active supervisor engine synchronizes the running-config and (or) the persistent configuration (if necessary) with the redundant supervisor engine.
• When you change the configuration, you must use the write command to allow the active supervisor engine to save and synchronize the startup configuration of the redundant supervisor engine.

Configuring Redundancy

To configure redundancy, perform this task:

When configuring redundancy, note the following:

• The sso keyword is supported in Cisco IOS Release 12.2(20)EWA and later releases.
• The rpr keyword is supported in Cisco IOS Release 12.1(12c)EW and later releases.

This example shows how to configure the system for SSO and display the redundancy facility information:

This example shows how to display redundancy facility state information:

This example shows how to change the system configuration from RPR to SSO mode:

This example shows how to change the system configuration from SSO to RPR mode:

Virtual Console for Standby Supervisor Engine

Catalyst 4500 series switches can be configured with two supervisor engines to provide redundancy. When the switch is powered, one of the supervisor engines becomes active and remains active until a switchover occurs. The other supervisor engine remains in standby mode.

Each supervisor engine has its own console port. Access to the standby supervisor engine is possible only through the console port of the standby supervisor engine. You must connect to the standby console to access, monitor or debug the standby supervisor.

The virtual console for a standby supervisor Engine enables you to access the standby console from the active supervisor engine without requiring a physical connection to the standby console. It uses IPC over EOBC to communicate with the standby supervisor engine, which emulates the standby console on the active supervisor engine. Only one active standby console session is active at any time.

The virtual console for the standby supervisor engine allows users who are logged onto the active supervisor engine to remotely execute show commands on the standby supervisor engine and view the results on the active supervisor engine. Virtual console is available only from the active supervisor engine.

You can access the standby virtual console from the active supervisor engine with the attach module, session module, or remote login commands on the active supervisor engine. You must be in privilege EXEC mode (level 15) to run these commands to access the standby console.

Once you enter the standby virtual console, the terminal prompt automatically changes to
hostname-standby-console where hostname is the configured name of the switch. The prompt is restored back to the original prompt when you exit the virtual console.

You exit the virtual console with the exit or quit commands. When the inactivity period of the terminal on the active supervisor engine where you logged in exceeds the configured idle time, you are automatically logged out of the terminal on the active supervisor engine. In this instance, the virtual console session is also terminated. Virtual console session is also automatically terminated when the standby is rebooted. After the standby boots up, you need to create another virtual console session.

To log in to the standby supervisor engine using a virtual console, enter the following command:

If the standby console is not enabled, the following message appears:

Note The standby virtual console provides the standard features that are available from the supervisor console such as command history, command completion, command help and partial command keywords.

The following limitations apply to the standby virtual console:

• All commands on the virtual console run to completion. It does not provide the auto-more feature; it functions as if the terminal length 0 command has been executed. It is also noninteractive. You cannot interrupt or abort an executing command by any key sequence on the active supervisor engine. If a command produces considerable output, the virtual console displays it on the supervisor engine screen.
• The virtual console is noninteractive. Because the virtual console does not detect the interactive nature of a command, any command that requires user interaction causes the virtual console to wait until the RPC timer aborts the command.

The virtual console timer is set to 60 seconds. The virtual console returns to its prompt after 60 seconds. During this time, you cannot abort the command from the key board. You must wait for the timer to expire before you continue.

• You cannot use virtual console to view debug and syslog messages that are being displayed on the standby supervisor engine. The virtual console only displays the output of commands that are executed from the virtual console. Other information that is displayed on the real standby console does not appear on the virtual console.

Synchronizing the Supervisor Engine Configurations

To manually synchronize the configurations used by the two supervisor engines, perform this task on the active supervisor engine:

Note Configuration changes made to the active supervisor engine through SNMP are not synchronized to the redundant supervisor engine. For information on how to handle this situation, see the “Supervisor Engine Redundancy Guidelines and Restrictions” section.

Note The auto-sync command controls the synchronization of the config-reg, bootvar, and startup/private configuration files only. The calendar and VLAN database files are always synchronized when they change. In SSO mode, the running-config is always synchronized.

This example shows how to reenable the default automatic synchronization feature using the auto-sync standard command to synchronize the startup-config and config-register configuration of the active supervisor engine with the redundant supervisor engine. Updates for the boot variables are automatic and cannot be disabled.

Note To manually synchronize individual elements of the standard auto-sync configuration, disable the default automatic synchronization feature.

Note When you configure the auto-sync standard, the individual sync options such as no auto-sync startup-config are ignored.

This example shows how to disable default automatic synchronization and allow only automatic synchronization of the config-registers of the active supervisor engine to the redundant supervisor engine, while disallowing synchronization of the startup configuration: