Spantree and PVST

From: Maik Bachmann (maik@Ironmaik.COM)
Date: Fri Mar 15 2002 - 12:16:12 EST


Hi,

one question on STP in a PVST environment.

In ieee802.1d there isn't a vlan-id carried in a BPDU, which is straight
forward since in the standard there exists only one STP which doesn't
care about any VLAN.

As far as I found since now, this i true for PVST as well (I dont't know
for PVST+, but I guess it's the same data structure).

What happens to STP in the following situation (assume the switches
to be newer generation 2948G and some other switches around which a
not part of interest):

    ------------ --------------
    | | P2/1 VLAN-10 | |
    | Switch1 |-----------------------------| Switch2 |
    | | VLAN-20 P2/1 | |
    ------------ --------------

We have 2 VLANS directly connected (I know - it's bad design - but thats
not the question). Will the STP coming from switch1 on VLAN-10 be extended
into switch2 or will the STP be broken since there are two distinct VLANS ?
If they will be broken - how is this accomplished (probably not thru BPDU
packets).

TIA
---Maik

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