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Posted by Thrill5 on July 4, 2008, 10:43 pm
VSS is similar to 3750 stacking but is not a "port" and is much more robust.
With VSS, both supervisors are active. The VSS link keeps both supervisors
in sync with each other. Updates to the mls and routing tables are sent to
the other supervisor, so that each "knows" what the other "knows". One
supervisor is called "active" and the other "standby" but this is a misnomer
because the "active" one is the one that is running the routing protocols,
and the control plane management, but both are making switching and routing
decisions independent of the other supervisor. (This is why it is called
VSS 1440, each supervisor has 720Gb/s of switching capacity and since both
are "active" you now have 1,440Gb/s of switching capacity.)
If the supervisor in a VSS pair fails, the entire chassis is dead; but the
other will keep working. If the "active" supervisor fails, the backup takes
over the routing protocols and control plane functions within 200ms, with
out loss of connectivity. (Routing protocols do NOT reset after a switch
over) If the VSS link fails but both supervisors are still working, there is
also a mechanism to detect this (that you must configure) and the active
supervisor will shut down all its ports to prevent both chassis from being
"active". The reason this is done is that if both supervisors are running
the routing protocols and management control plane, the rest of the network
will get confused because you now have two independent switches running with
the same ip addresses.
> Do I understand correctly, that the VSS 1440 is a port of the well known
> stacking mechanisms known from other switches?
>
> So if the supervisor board VS-... will have an (on board) power outage,
> the
> 10GE connectors are not able to keep the system up and running using the
> working supervisor in the other chassis, or do they survive?
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