The 2950/60 3550, it does nott care if it carries IPv4, v6 or whatever else type of traffic when working at L2. You won't be able to have an IPv6 address for mgmt on the 2950 - BTW.
The 3350 is limited on what IPv6 it can run. 12.2(50) would work. It is just software, no ASIC support.
Thats fine, I understood. Whether we use IPv4 or v6; its L3. Switch work on L2 and its ethernet. so no need to bother.
What about L3 switch, when using IPv6 HSRP do we need to upgrade. Im using 12.2(35)SE5 for 3560 switch with IPv4 HSRP. When I check in fn, seems ok.