Showing results for 
Search instead for 
Did you mean: 

Interface on standby SSO is active?

Level 1
Level 1

If a switch with redudant SUP as SSO is connected to two of switches with HSRP, interfaces on standby SUP is active? If then, may I know how it work?

Sent from Cisco Technical Support iPad App

1 Reply 1

Arumugam Muthaiah
Cisco Employee
Cisco Employee

Hi Casinamul,

Yes, Interfaces on the stanby supervior active. Please see the detail below,

1. The two Gigabit Ethernet interfaces on the redundant supervisor engine are always active unless you enter the

fabric switching-mode allow dcef-only command

2. With a Supervisor Engine 720, if all the installed switching modules have DFCs, enter the fabric switching-mode allow dcef-only command to disable the Ethernet ports on both supervisor engines, which ensures that all modules are operating in dCEF mode and simplifies switchover to the redundant supervisor engine


Supervisor Engine 720-10GE Restrictions

In RPR redundancy mode, the ports on a Supervisor Engine 720-10GE in standby mode are disabled.

HSRP and SSO Working Together

The SSO HSRP feature enables the Cisco IOS HSRP subsystem software to detect that a standby RP is installed and the system is configured in SSO redundancy mode. Further, if the active RP fails, no change occurs to the HSRP group itself and traffic continues to be forwarded through the current active gateway router.

Prior to introduction of the SSO HSRP feature, when the primary RP of the active router failed, it would stop participating in the HSRP group and trigger another router in the group to take over as the active HSRP router.

SSO HSRP is required to preserve the forwarding path for traffic destined to the HSRP virtual IP address through an RP switchover.

Configuring SSO on the edge router enables the traffic on the Ethernet links to continue during an RP failover without the Ethernet traffic switching over to an HSRP standby router (and then back, if preemption is enabled).


SSO HSRP alters the behavior of HSRP when a router with redundant Route Processors (RPs) is configured for stateful switchover (SSO) redundancy mode. When an RP is active and the other RP is standby, SSO enables the standby RP to take over if the active RP fails.

With this functionality, HSRP SSO information is synchronized to the standby RP, allowing traffic that is sent using the HSRP virtual IP address to be continuously forwarded during a switchover without a loss of data or a path change. Additionally, if both RPs fail on the active HSRP router, then the standby HSRP router takes over as the active HSRP router.

The feature is enabled by default when the redundancy mode of operation is set to SSO.




*** Please rate if the post is useful ***

Regards, Aru *** Please rate if the post useful ***
Review Cisco Networking for a $25 gift card