01-10-2008 07:28 AM - edited 03-05-2019 08:23 PM
I have two core 6509 switches (one upstairs and one down stairs, not redundant) with two 3560 switches trunked up to one of the 6509s.
I would like to add a third 3550 switch to use as a spare upstairs, in case one of the blades fails on the 6509.
I want to use a fiber link between the two and want to make sure I do not interrupt STP too much.
Is there anything precautionary I need to do to prevent any problems?
The only config on the core switch switch is:
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
I see no priority set up anywhere
01-10-2008 07:35 AM
You should configure STP priority on the 6500 switches as there is a high chance the 3550 can become the STP root for all Vlans.
Some 3550s can be older than 6500s hence a lower MAC Address. Lower MAC Address = Higher change of becoming STP root on an election.
HTH,
__
Edison.
01-10-2008 08:17 AM
Thanks Edison,
As always useful information.
Can I just set the priority on the fly without any problems or interruptions?
Can the priority be set globally, or does it have to be set up per VLAN?:
spanning-tree vlan 1 priority 28672
The two core switches are showin Priority on all of the VLANs
The current values for the two switches are:
KLD-6509-RTR-1#sh spanning-tree brief
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 16384
Address 00d0.01cd.1001
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 16384
Address 00d0.01cd.1001
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
LKLD-6509-RTR-2#sh spanning-tree brief
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 16384
Address 00d0.01cd.1001
Cost 4
Port 641 (GigabitEthernet6/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address 00d0.01e0.7401
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
01-10-2008 08:29 AM
You can set it globally or per-vlan, it depends on the design you want to achieve. Usually, if I have 2 Core Switches, I select one switch to handle all the 'even' Vlans and another switch to handle all the 'odd' Vlans.
Again, the priority on both switches should be set lower than the default 32768
For instance if switch '1' would handle all odd Vlans, the priority would be
spanning-tree vlan 1,3,5 priority 0 (to be the primary switch) and
spanning-tree vlan 2,4,6 priority 4096 (to be the secondary switch in case switch '2' fails).
Do the opposite on switch '2'.
01-10-2008 09:13 AM
Thanks Edison,
Will this distrupt anything making this change?
Is there any danger of causing a problem?
Also, looking at the switch I want to put in the network, it shows:
"No spanning tree instances exist"
when I do a "sh spanning-tree brief"
Is this because it is not linked to any other switches?
01-10-2008 10:47 AM
Make the changes during non-business hours. A calculation may take place when you implement those commands causing a slight disruption on how packets are forwarded.
As for:
"No spanning tree instances exist"
means the switch doesn't have any active Vlan running Spanning-Tree. If you connect a workstation to a switchport and associate the switchport to an existing Vlan, the output will show the active Vlan. A connection to another switch isn't needed for viewing Spanning-Tree instances.
01-10-2008 12:51 PM
Thanks for the great information.
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