3750 and Crossstack Uplinkfast

[keithyam]

I have stack of 3750s as access switches, running CSUF within the stack. So there is only one forwarding uplink in the stack at one time. Top and bottom in the stack are connected to a pair of upstream distribution switch as usual.

Would it buy me anything to dual home each of the stacked switch individually to 2 upstream switches, ON TOP OF the existing stacking? Would it make the original CSUF converge even faster if one of the upstream switch is lost ?

As a side note: I don't want to lose the benefit of 3750 stacking as it gives me 32G instead of 1G in 3550 stacking. Correct me if I'm wrong on this "to stack or not to stack" argument.

[Craig Norborg]

Ok, first you have to realize that stacking on a 3750 is quite different than stacking on most other switches. If you're stacking via the cable on the back, CSUF doesn't apply. CSUF would only apply when stacking the switches via their gigabit ports, in which case you lose the 32G uplink.

When 3750's are stacked together via the cable on back, you should think of them more of as one big switch, rather than a set of stacked switches. That's really how they work.

If you multihomed each 3750 to your two upstream switches and had spanning tree configured, I believe only 1 of your uplinks should be unblocked via STP at a time. If you want additional bandwidth as well as redundancy, you might consider cross-stack channelling to the upstream switches, that would allow you to have more ports actively passing data (even though they would be a single channel) at a time, while still adding some redundancy.

But you first must stop confusing the 3750's stacking with the older GBIC stacking, they are not the same thing. CSUF only affects how spanning-tree works on GBICs and not how the 3750's stacking mechanism. Spanning-tree doesn't affect 3750's internally to their stacks!!