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New Member

Finding Root Bridge CatOS/CATIOS

Any easy way to find the root bridge? have 6513, 6509, several 2950's and 2948G's.

I know of the show spantree Summary etc. But I have no idea what mac address being returned goes to what switch.

what is cmd to get the mac of switch with CatOS and CatIOS that is being used to determine the root bridge.

Any links appreciated.

Hall of Fame Super Silver

Re: Finding Root Bridge CatOS/CATIOS

Hello Doug,

you have to follow the path to the root bridge:

be aware that the root bridge can be different for each vlan if you use PVST+ or rapid PVST or for each instance (if using MST 802.1s)

sh spantree vlan#

provides you these informations

then you move to the next switch following the root port.

if you have CDP enabled this is easy just does

sh cdp n mod/num

where mod/num is the root port.

Repeat the steps until you reach the root bridge.

Hope to help


New Member

Re: Finding Root Bridge CatOS/CATIOS

What is weird is my "core" switch were everything connects isn't the root bridge. I inherited this network, so time for some fixing.

panning tree mode: RAPID-PVST+

Runtime MAC address reduction: enabled

Configured MAC address reduction: enabled

Root switch for vlans: none.

Global loopguard is disabled on the switch.

Global portfast is disabled on the switch.

BPDU skewing detection disabled for the bridge.

BPDU skewed for vlans: none.

Portfast bpdu-guard enabled for bridge.

Portfast bpdu-filter disabled for bridge.

Uplinkfast disabled for bridge.

Backbonefast disabled for bridge.

L2PDU rate limiter is disabled.


Re: Finding Root Bridge CatOS/CATIOS

I am sure you can change that once you have identified all the switches MAC and priority ID. You can set the core as the root by changing its VLAN priority ID.


New Member

Re: Finding Root Bridge CatOS/CATIOS

yes, the CDP cmd was what I was looking for.


Re: Finding Root Bridge CatOS/CATIOS

I believe that "sh hard" will have the MAC address of the switch. Here is an output of one my switch. Some lines are omitted:

cisco WS-C3560-48PS (PowerPC405) processor (revision M0) with 122880K/8184K bytes of memory.

Processor board ID CAT0936Z1QA

Last reset from power-on

2 Virtual Ethernet interfaces

48 FastEthernet interfaces

4 Gigabit Ethernet interfaces

The password-recovery mechanism is enabled.

512K bytes of flash-simulated non-volatile configuration memory.

Base ethernet MAC Address : 00:15:62:F4:EE:80

sh span vlan 4


Spanning tree enabled protocol ieee

Root ID Priority 32772

Address 0015.62f4.ee80

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32772 (priority 32768 sys-id-ext 4)

Address 0015.62f4.ee80

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 300

Interface Role Sts Cost Prio.Nbr Type

------------------- ---- --- --------- -------- --------------------------------

Fa0/41 Desg FWD 19 128.45 Shr Edge

Fa0/47 Desg FWD 19 128.51 P2p Edge

Po1 Desg FWD 3 128.56 P2p

you can see the MAC address from sho hard and it appears in the sh span vlan 4.



Re: Finding Root Bridge CatOS/CATIOS

For each vlan do a "show spanning tree vlan # for IOS and show spantree for catos . This will give you the root bridge and the root port if the switch is not the root for the vlan , just follow the root port until you find the root for each vlan . For catos you can use "set spantree vlan X root primary to set root on catos box. For IOS use " spantree vlan X root primary " .

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