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How you might use VSS would be to have your pair of 4500s use VSS (if they're able). This would allow active L2 redundancy. E.g. uplink port-channel from edge switches with a link to each 4500.
Keep L3 between the 4500s and 6509s, don't VSS the 6509s. (You could also VSS pair the 6509s, but unless you believe there's a really good reason to do so, again, I suggest you don't. VSS is really more of a benefit for L2 than it is for L3.)
You can do VSS on distribution layer and port channel down to access layer switches, this port channel will carry L2 VLAN(s) and will be terminated on distribution layer (C4500x).
Since now you have ONE distribution switch so you only need 2 x L3 links between your distribution switch to your core C6509 switches, while before VSS you would have 4 x L3 links between distribution and core.
What we did is to covert 4 x L3 /30 links between distribution and core switches into 2 x L3 /30 port channels. For example:
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...