Hi Brendan,
You will be having very less chance the chassis will go down. You are already have power redundany and supervisor redundancy.
I feel that it is not necessary to add redundant chassis only for backup of primary switch failure. If you would like to add one more switch, you can deploy it for better traffic management and this will provide chassis level redundancy as well. It depends on your need.
The below detail will explain how to utilize the dual supervior efficiently.
When you configure the both supervisor in NSF/SSO, the standby will take over the active role without any interruption on the production network.
NSF/SSO
In September of 2004, the Cisco Catalyst 4500 introduced its capability to support the SSO mode of supervisor redundancy. SSO was initially supported on the Cisco Catalyst 4500 with Cisco IOS Software Release 12.2(20)EWA. With SSO, the functionality of the supervisors is the following:
- The standby supervisor performs a complete boot without suspending at the Cisco IOS Software init process.
- Each feature synchronizes its internal state between the active and standby supervisors.
- Changes made to the running configuration are synchronized to the standby.
- Physical links remain up, and L2 protocols are not reset, yielding minimal packet loss, less than 200 ms of traffic loss.
SSO is the component of the solution that synchronizes and saves state information between the active and standby supervisors such that Layer 2 connectivity protocols are maintained.
In order to preserve L3 protocol state information, NSF was developed. As the acronym states, NSF allows for continued forwarding of data packets along known routes while the routing protocol information is recovered and validated gracefully, avoiding unnecessary route flaps and network instability. The NSF capability was introduced on the Cisco Catalyst 4500 in Cisco IOS Software Release 12.2(31)SG. NSF capability requires a redundant system to run in SSO mode.
Nonstop Forwarding (NSF)
NSF works with SSO to minimize the amount of time the network is unavailable following a supervisor engine switchover.
NSF provides these benefits:
Improved network availability: NSF continues forwarding network traffic and application state information so that user session information is maintained after a switchover.
- Prevents routing flaps: NSF continues forwarding routing traffic while reestablishing routing relationships
- Improves network stability: Network stability is improved by avoiding routing flaps.
- Neighboring routers do not detect a link flap: Because the interfaces remain up during a switchover, neighboring routers do not detect a link flap.
- Maintains user sessions established prior to the switchover.
Refer:
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps4324/prod_white_paper0900aecd806f0663.html
Regards,
Aru
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Regards,
Aru
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