Pruning on 3500 and 3550 series switches

This morning, I set up a lab experiment to show my students
how pruning worked. However, after we pruned, the distant switch was
still getting the frames from the pruned VLAN. We know that is true
because we could still ping a PC that was connected to that switch
over the VLAN. By my understanding, we shouldn't have beena able to
ping it any more after that VLAN was pruned towards it.

Does anyone have any information to shed some light on this
mystery? URLs with a solution would be greatly appreciated.

Regards,



Fred

 

after we pruned, the distant switch was

VLAN pruning is intended to prevent Broadcast and
Unknown traffic from being needlessly
flooded along trunks in the case where the
VLAN has no active ports on the far side of the trunk
from the source of the traffic.

In that case pruning would be inappropriate
since the traffic is required to cross the link.

For what it's worth I have never liked the idea
anyway.

- Few such links are likely in (most) well designed networks.
- Process sounds complex and potentially
problem prone.
- I expect that few people use it so you will
be a beta tester.

Good for a class though, you need to know

addressing (L2)
learning
forgetting
forwarding decisions
flooding
vlans
trunking
more?

If they can get their
little heads well enough round this to correctly
predict behaviour then they will be ahead of
. . .
some professors.<g>

I doubt though if the educational potential
was a consideration for Cisco when they
spent the money to put it in.

Maybe the VLAN Policy Server thing
was put in just for such an eventuality too?
I suspect that it though has gone.