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New Member

VSS confusion

I have a VSS setup, Sw1(Active) & Sw2(Standby) Am running ISSU loadversion on Sw1, So Sw2(Standby) will reload at the time when Sw2(standby) is loading as standby, am giving reload command on Sw1(Active).

Now what behavior i observed is both the box got reloaded.

According to my knowledge Sw1(Active) am giving reload command so only the Sw1(Active) box should reload and Sw2(Standby) which is reloading, it should boot as active. Please confirm this.



VIP Super Bronze

What type of devices are you

What type of devices are you using?  If you are using 6500 series, then the reload command on the primary will reload both primary and backup.  if you want to reload only one of the devices, then reload shelf 1 or 2 should be used, but the behavior is different when you are using 4500x.


New Member

Thanks for the great info

Thanks for the great info Reza & Leo.

@Reza we are using 4500 box.. I just want to get confirm when the standby box reloading in active if we give reload will it reload both? My doubt is if the standby box reloading and we are giving the reload command on active, According to my knowledge reload means it should reload itself not the both box. This is what i feel bit confusing. Please help me out.Looking for the answer from you EXPERT'S.


Hi, See this:1-When you enter


See this:

1-When you enter the issu loadversion command, the entire VSS standby chassis, including the supervisor engine and modules, is reloaded with the new upgrade image. Because the VSS standby chassis modules are unavailable while reloading, the throughput of the VSS is temporarily reduced by 50 percent during this stage. After reloading, the VSS standby chassis boots with the new image and initializes in SSO mode, restoring traffic throughput. In this state, the VSS standby chassis runs a different software version than the VSS active chassis, which requires the VSS active chassis to communicate with modules running different image versions between the two chassis.



2-When the VSS standby chassis is successfully running the new image in SSO mode, you can enter the issu runversion command. This command forces a switchover in which the upgraded VSS standby chassis takes over as the new VSS active chassis. The formerly VSS active chassis reloads and initializes as the new VSS standby chassis in SSO mode, running the old image. As in the loadversion stage, the throughput of the VSS is temporarily reduced during the VSS standby chassis reload, and the VSS standby chassis runs a different software version than the VSS active chassis.


Hope this helps.

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