Supervisor Redundancy

On modular switches with redundant supervisor modules, the standby supervisor switch can take control to minimize downtime and data loss in the case of an active supervisor's reset, reload, or failure. The redundancy protocol configured on the active supervisor determines the switchover.

Use the show redundancy status command to display both the supervisors' state and the current redundancy protocol. Use the show redundancy file-replication command to display the state of configuration file synchronization between the supervisors,

Redundancy Supervisor Protocols

There are three available supervisor redundancy protocols.

Route Processor Redundancy (RPR)

The default redundancy protocol is Route Processor Redundancy (RPR), which synchronizes startup-config files between the supervisor modules and partially boots the standby supervisor to a standby warm state but does not synchronize running-config. If the active supervisor fails or a manual switchover initiates with the redundancy manual switchover command, the standby supervisor will become active. The running state, including the spanning tree, is lost, bringing down all links temporarily.

Under RPR, you can access the CLI of the standby supervisor by SSH or through the console port, but the available command set is limited. Any configuration changes made to the standby supervisor will be lost when the supervisor reboots.

Stateful Switchover (SSO)

In the Stateful Switchover (SSO) protocol, the switch synchronizes startup-config and running-config files between the supervisor modules. It fully boots the standby module to a standby hot state to speed up the switchover process and minimize packet loss. If the active supervisor fails or a manual switchover initiates, the standby supervisor immediately becomes active, and the L2 running state is maintained. An SSO switchover is largely transparent from the outside. Still, because the L3 state is not synchronized, the switchover can result in traffic loss for traffic forwarded on routes learned by a dynamic routing protocol. Enabling nonstop forwarding can eliminate most packet loss for BGP and OSPF.

Under SSO, the console port can access the CLI of the standby supervisor, and the command set is limited. Any configuration changes made on the standby supervisor will be lost when the supervisor reboots.

Note: When upgrading the EOS on a dual-supervisor switch to an SSO-capable version (4.11.0 or higher) from a version that does not support SSO, both supervisors will reset simultaneously, causing several seconds of system downtime.

Simplex

When a simplex protocol is on the switch, the standby supervisor is disabled, and switchover will not occur even if the active supervisor fails. To reload the active supervisor results in system downtime while the supervisor reboots and the standby supervisor remains disabled. The redundancy protocol must change to RPR or SSO to transfer control of the switch to the standby supervisor.

Under the simplex protocol, the console port can access the CLI of the disabled supervisor, and the command set is limited. Any configuration changes made on the standby supervisor will be lost when the supervisor reboots.

Configuring Supervisor Redundancy

To configure the supervisor redundancy protocol, use the protocol command in redundancy configuration mode (accessed with the redundancy command).

Changing the redundancy protocol on the active supervisor resets the standby supervisor regardless of redundancy protocol, and executing the write command on the active supervisor synchronizes the startup-config files between supervisors in RPR and SSO modes.

Examples

  • These commands display the current redundancy state of the switch and the most recent file synchronization information.
    switch# show redundancy state
  my state = ACTIVE
peer state = STANDBY WARM
      Unit = Primary
   Unit ID = 1

Redundancy Protocol (Operational) = Route Processor Redundancy
Redundancy Protocol (Configured) = Route Processor Redundancy
Communications = Up
Ready for switchover

  Last switchover time = 7:23:56 ago
Last switchover reason = Supervisor has control of the active supervisor lock
switch# show redundancy file-replication
0 files unsynchronized, 2 files synchronized, 0 files failed, 2 files total.

File                   Status         Last Synchronized
---------------------- -------------- -------------------
file:persist/sys       Synchronized   0:10:04 ago
flash:startup-config   Synchronized   0:10:04 ago
switch#

  • These commands set the redundancy protocol for the active supervisor to stateful switchover (SSO).
    switch# config
switch(config)# redundancy
switch(config-redundancy)# protocol sso
Peer supervisor will be restarted.
switch(config-redundancy)#