Add New switch to network

Unanswered Question
Jan 10th, 2008

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

I have this problem too.
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Edison Ortiz Thu, 01/10/2008 - 07:35

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.

wilson_1234_2 Thu, 01/10/2008 - 08:17

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

Edison Ortiz Thu, 01/10/2008 - 08:29

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'.

wilson_1234_2 Thu, 01/10/2008 - 09:13

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?

Edison Ortiz Thu, 01/10/2008 - 10:47

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.

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