Your output shows some unexpected content in this case. I would have
expected the path costs to be equal. Did you experiment with some of the
fine-tuning options of STP? Also, are you sure that you are not channeling
(Etherchannel)? On the larger Cats (4k, 6k, etc.) PAGP runs by default and
creates a channel wherever it can. This means that instead of shutting down
the redundant port (both ports destined for the same switch), it will create
a virtual channel using them both (up to 4 physical ports). STP will see
this as only a single link, however. I don't believe that PAGP is on by
default on these models, but I could be wrong.
One other thing to possibly check is the VTP information. If you are not
running VTP, then you will have to manually create corresponding VLANs on
each switch. I don't see any mention of other VLANs other than VLAN1
(default), but that should propagate with no problem. The idea here is, if
you are having STP issues on a particular VLAN, and keeping in mind that
Cisco implements a per-vlan STP, then it's possible that VLAN info is not
propagating from one switch to the other as a result of misconfigured VTP,
VLANs, or trunking.
Please share the entire config and maybe something else will jump out.
Rik
-----Original Message-----
From: Pierre-Alex [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, February 13, 2001 4:08 PM
To: [EMAIL PROTECTED]
Cc: Dale Cunningham
Subject: DISTURBING: Spanning Tree Protocol Does not Work.
Or I am really dumb....
I have two switches a Cisco 2924XL-EN and a Cisco 1912-EN. I have setup port
A and port B of the 1912 swictch to do ISL trunking with the 2924XL
This situation should have created a loop and the Spanning Tree protocol
should have disabled port B.( I have setup the 2924XL to be the root).
Instead I am getting the
following output, with both port A and B in the fowarding mode (see below)
So either the Spanning Tree protocol did not do its job (with due respect to
its creator),
or the trunking ports are not part of the spanning tree calculation, or I am
really dumb and I missed something in the story ....
Any comment?
DISL state: On, Trunking: On, Encapsulation type: ISL
C1912#sh trunk b
DISL state: On, Trunking: On, Encapsulation type: ISL
Port FastEthernet 0/26 of VLAN1 is Forwarding
Port path cost 10, Port priority 128
Designated root has priority 32768, address 0050.3EF0.3580
Designated bridge has priority 32768, address 0050.3EF0.3580
Designated port is 22, path cost 0
Timers: message age 20, forward delay 15, hold 1
--More--
Port FastEthernet 0/27 of VLAN1 is Forwarding
Port path cost 10, Port priority 128
Designated root has priority 32768, address 0050.3EF0.3580
Designated bridge has priority 32768, address 0050.50E2.42C0
Designated port is 27, path cost 10
Timers: message age 20, forward delay 15, hold 1
Pierre-Alex
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