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VLAN Trunking - can you filter which ports are in a given trunk?

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I have a network which looks something like the rough diagram below

| C3700 series |
| |
| Link A
--------------- Link B ---------------
| C3508 Switch|------------|C2950 Switch |
| "D" | | "A |
-------------- --------------
| Link C
|C2950 Switch |
| "C" |

Each C2950 is a "T" model, and has a gigabit link back to the 3508,
and also has other switches cascaded off it.

Link A, Link B & Link C are all trunks.

I have VLAN's numbered 2, 3, 4, 5 for example, and I want to have the
following happen

Link A carries traffic for all VLAN's
Link B Carries traffic for VLAN's 2, 4 & 5
Link C Carries traffic for VLAN 3 only

Is this possible? I've attempted to use the commands

switchport mode trunk
switch port trunk allowed vlan 3

on the port being used for linking switch "C" with switch "D", but I can
find no indication that it's actually working.

Is there some way of monitoring which VLAN's are actually being trunked
out a given port using debug or a show option, or as I asking too much?

The 2950T's are running software version 12.1(14). The 3508 is running
software version 12.0(5.1) as they are somewhat older.

Any help appreciated


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