spanning tree root ID--Mac-address question

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May 9th, 2008
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Hi ,

when i do

sh spanning-tree


VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 000b.be50.ed40

This bridge is the root

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

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)

Address 000b.be50.ed40

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

Aging Time 300


Interface Port ID Designated Port ID

Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr

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

Fa0/1 128.1 19 FWD 0 32769 000b.be50.ed40 128.1

Fa0/2 128.2 100 FWD 0 32769 000b.be50.ed40 128.2

Fa0/3 128.3 19 FWD 0 32769 000b.be50.ed40 128.3

Fa0/4 128.4 19 FWD 0 32769 000b.be50.ed40 128.4

Fa0/5 128.5 19 FWD 0 32769 000b.be50.ed40 128.5

Fa0/6 128.6 19 FWD 0 32769 000b.be50.ed40 128.6

Fa0/8 128.8 19 FWD 0 32769 000b.be50.ed40 128.8

Fa0/10 128.10 19 FWD 0 32769 000b.be50.ed40 128.10

Fa0/11 128.11 19 FWD 0 32769 000b.be50.ed40 128.11

Fa0/13 128.13 19 FWD 0 32769 000b.be50.ed40 128.13

Fa0/15 128.15 19 FWD 0 32769 000b.be50.ed40 128.15



My question is how we cfan find root port?i try this command

sh mac-address-table address 000b.be50.ed40

Mac Address Table

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


Vlan Mac Address Type Ports

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

no luck

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Collin Clark Fri, 05/09/2008 - 07:29
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show spanning-tree bridge address will show the MAC address of the bridge you are on.


If you are looking for the root port on a switch show spanning-tree root port.


Hope that helps.

mahesh18 Fri, 05/09/2008 - 07:52
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thanks for reply

when i do command

show spanning-tree bridge address

show spanning-tree root port

VLAN0001 This bridge is root

this comes

show spanning-tree bridge address

VLAN0001 000b.be50.ed40


Collin Clark Fri, 05/09/2008 - 08:09
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The bridge you are on is the root bridge (as Jon stated). It's using the system MAC, so you will not see it in the ARP table. Another way (probably not 100% effective) to find the system MAC is take the MAC of fa0/1 and subtract 1. In your case the MAC address of your fa0/1 interface should be 000b.be50.ed41. Is that correct? The safer method is the show spanning-tree bridge address.

Istvan_Rabai Fri, 05/09/2008 - 07:41
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Hi Mahesh,


This bridge will not have a root port because it is the root bridge itself.


See "This bridge is the root" statement under

Root ID Priority 32769

Address 000b.be50.ed40


For non-root bridges it would show up among the ports in FWD or BLK state.


Cheers:

Istvan


mahesh18 Fri, 05/09/2008 - 10:19
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thanks for reply

how can i find root bridge and root port in the network

Istvan_Rabai Fri, 05/09/2008 - 10:35
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Hi Mahesh,


The "show spanning-tree root" command will show you the root bridge IDs for all vlans that the local switch participates in.


The easiest way to find a root port on a switch is the "show spanning-tree vlan x" command for a given vlan.


Applying this command repetitively and following the root ports up through several non-root switches will lead you to the root switch.


Cheers:

Istvan

Jon Marshall Fri, 05/09/2008 - 07:42
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Mahesh


Just to add to Collin's post. This switch will not have a root port for vlan 1 because it is the root bridge ie.


VLAN0001

Spanning tree enabled protocol ieee

Root ID Priority 32769

Address 000b.be50.ed40

This bridge is the root <----------


Root bridges should only have designated ports in the vlans they are root for.


Jon

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