nope.
thats wrong...
it's four steps.
1. lowest root BID
2. lowest path cost
3.lowest sending BID
4.Lowest port ID.
all of which are contained in a Config BPDU.
this is also part of how the root bridge is established...
-Peter Slow, CCNP Voice Guy
----- Original Message -----
From: "Buri, Heather H"
To:
Sent: Wednesday, May 30, 2001 1:20 PM
Subject: question regarding spanning tree [7:6485]
> Hello.
>
> I don't really have a problem so much as I am trying to get a better
> understanding of how Spanning Tree works. I am currently studying for my
> switching exam and am reviewing Spanning Tree. I have the following
> statement from the Cisco course manual and in the case of redundant paths
to
> the root bridge, it states "In order to choose which port will be
forwarding
> data and which ports will be blocking data, the switch looks at two
> components in the BPDU, as follows:
>
> 1. Path Cost
>
> 2. Port ID
>
> The switch looks at the path cost first to determine which port is
receiving
> the lowest cost path. If the path cost is equal, as in the case of
parallel
> links, the bridge goes to the port ID as a "tie-breaker". The port with
the
> lowest port ID forwards and all other ports block."
>
> I decided to verify this on one of my 4006's which connects to my 6509
> (which is the root) and here is what I found:
>
> pet4006_8 (enable) sh spantree statistics 1/2 1
> Port 1/2 VLAN 1
>
> SpanningTree enabled for vlanNo = 1
>
> BPDU-related parameters
> port spanning tree enabled
> state forwarding
> port_id 0x8002
> port number 0x2
> path cost 4
> message age (port/VLAN) 0(20)
> designated_root 00-d0-01-98-5c-00
> designated_cost 0
> designated_bridge 00-d0-01-98-5c-00
> designated_port 0x8087
> top_change_ack FALSE
> config_pending FALSE
> port_inconsistency none
>
> PORT based information & statistics
> config bpdu's xmitted (port/VLAN) 0(8702816)
> config bpdu's received (port/VLAN) 831061(1662121)
> tcn bpdu's xmitted (port/VLAN) 1(1)
> pet4006_8 (enable) sh spantree statistics 1/1 1
> Port 1/1 VLAN 1
>
> SpanningTree enabled for vlanNo = 1
>
> BPDU-related parameters
> port spanning tree enabled
> state blocking
> port_id 0x8001
> port number 0x1
> path cost 4
> message age (port/VLAN) 1(20)
> designated_root 00-d0-01-98-5c-00
> designated_cost 0
> designated_bridge 00-d0-01-98-5c-00
> designated_port 0x80c8
> top_change_ack FALSE
> config_pending FALSE
> port_inconsistency none
>
> However, as you can see from the above output, Port 1/2 is the port chosen
> to forward and it appears to have a higher port ID number. Can someone
> please explain what I am missing here?
>
> Thanks!
>
> Heather Buri
> CSC Technology Services - Houston
>
> Phone: (713)-961-8592
> Fax: (713)-961-8249
> Mobile:
> Alpha Page:
>
> Mailing: 1360 Post Oak Blvd
> Suite 500
> Houston, TX 77056
>
>
>
> EOM
>
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