04-25-2007 03:55 AM - edited 03-05-2019 03:40 PM
Hi,
how can i find out whitch Switch is the root bridge for my network, if i have only access to one switch and this one is not the root bridge?
Thanks in advance
04-25-2007 04:17 AM
Hi Friend,
When you issue "sh spanning-tree" command you will get the root bridge mac address for vlans you have in your network.
Then you can follow that mac address issuing "sh mac-address-table address
Telnet to next switch and follow the same procedure till you see in "sh spanning-tree" bridge id mac address and root id mac address are same.
Yes for this you need to have an access of all the switches and staying at one switch it is not possible to find who is the root bridge till the time you have documented that mac address with switch details.
HTH
Ankur
04-25-2007 10:53 PM
Hello ,
Looking for some information on this matter.
By whcih command L3 switch makes itself as Root Switch.
Can you pls let me know wht command we use for this activity.
Thanks.
~Akber Mirza.
04-25-2007 11:03 PM
Hi Akber,
"spanning-tree vlan
Which L3 switch do you have?
HTH
Ankur
*Pls rate all helpfull post
04-25-2007 11:15 PM
AnkurThanks for the above information.
We have 6509 L3 switch. We have Vlan 1,484&784 configured on this switch.
please see the below info on sh spantree:
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address 0015.2cf0.6001
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address 0015.2cf0.6001
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Gi2/0/1 Desg FWD 4 128.129 Edge P2p
Gi2/0/2 Desg FWD 4 128.130 Edge P2p
VLAN0484
Spanning tree enabled protocol ieee
Root ID Priority 10
Address 0015.c715.cde3
Cost 3
Port 1665 (Port-channel101)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address 0015.2cf0.61e4
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po101 Root FWD 3 128.1665 P2p
VLAN0784
Spanning tree enabled protocol ieee
Root ID Priority 10
Address 0015.c715.cf0f
Cost 3
Port 1665 (Port-channel101)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address 0015.2cf0.6310
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po101 Root FWD 3 128.166
==============================================
In my switch Vlan 1 is shutdown and other two vlans are L3 vlans. but as per the above information root bridge is shown only in vlan 1.
can you pls explanin .
~Akber
04-25-2007 11:32 PM
Hi Akber,
For VLAN 484 and VLAN 784 root mridge mac address is Address 0015.c715.cde3 for vlan 484 and Address 0015.c715.cf0f for vlan 784.
So you can trace this mac address in your network to find which switches have declared themselves as root bridge for these 2 vlans.
Also you can check if there is any priority configured on those switches to become root?
Regards,
Ankur
04-26-2007 05:36 AM
Hello Ankur,
Thanks for the above information.
Please see belwo the Rott switch status and priority details .
cs102-hy2> (enable) sh spantree summary
Spanning tree mode: RAPID-PVST+
Runtime MAC address reduction: disabled
Configured MAC address reduction: disabled
Root switch for vlans: 484,784.
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.
set spantree priority 10 484
set spantree priority 10 784
Can you explain me by which command they becoming Root Switch on cs102-hy2.
Moreover I dont see any where it is manually defined Root Switch by giving spanning-tree vlan
Can u explain me how the root switch is getting selected.
~Akber.
04-25-2007 11:35 PM
Hi Akber
The output is telling you that your root bridge for vlan 484 & vlan 784 are on different switches.
What switch is at the end of port-channel 101. Could you send the spanning-tree config for that switch.
Jon
04-26-2007 05:38 AM
Hello Jon,
Thanks for the above information.
Please see belwo the Rott switch status and priority details .
cs102-hy2> (enable) sh spantree summary
Spanning tree mode: RAPID-PVST+
Runtime MAC address reduction: disabled
Configured MAC address reduction: disabled
Root switch for vlans: 484,784.
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.
set spantree priority 10 484
set spantree priority 10 784
Can you explain me by which command they becoming Root Switch on cs102-hy2.
Moreover I dont see any where it is manually defined Root Switch by giving spanning-tree vlan
It is a 6509 cat OS switch ,server access switch .
Can u also tell me why Vlan 1 in my previous config is used for SPT as it is not used for any of the ports and.
Can u explain me how the root switch is getting selected.
04-26-2007 05:47 AM
Hi Akber
The two lines
set spantree priority 10 484
set spantree priority 10 784
are what makes this the root bridge for those vlans. The default priority on a switch is 32768 so someone has explicitly set this switch up with this priority.
Generally speaking you usually set root bridge one of 2 ways
set spantree priority 8192
set spantree root 484,784
8192 is generally used for spanning-tree root and 16384 for spanning-tree secondary.
The better way to set is the second way. Ankur gave you the equivalent command for IOS. The above commands are CatOS which is what your switch is running.
HTH
Jon
04-26-2007 06:06 AM
Thanks a ton friend for the input!
From my knowledge, the highest bridge ID priority will be elected as Root switch.
If you define a low bridge ID how will it become root bridge as per your above inputs.
Can you also tell me why we are configuring root bridge as server access switch (In Access layer cs102-hy2) ,rather configuring root as L3 switch (In Dist layer cr3-hy2).
Please need your valuable input .
Many Thanks.
~Akber.
04-26-2007 06:15 AM
Hi Akber
The bridge with the lowest priority becomes the root bridge for that vlan not the highest.
Without knowing your topology it's difficult to say why your access layer switch is configured as root for this vlan. Generally speaking you don't make access-layer switches as your STP root bridges as this can lead to inefficient L2 paths but it all depends on your vlan distribution and your traffic flows.
Again, generally speaking you have your core/distribution switches as root and secondary but this is only a guideline.
HTH
Jon
04-27-2007 05:29 AM
Hello John,
So I got to know that, Priority and Bridge priority are different from you words.
I have difficulty in understanding the following scenario.
cs401-hy2 makes itself as Root for 497/797,
though i see priority set as 10 on both cs101/cs401 switches .
can u plz expalin how cs401-hy2 is becoming root for 797.
cs101-hy2> (enable) sh spantree
VLAN 1
Spanning tree mode RAPID-PVST+
Spanning tree type ieee
Spanning tree enabled
Designated Root 00-00-00-00-00-00
Designated Root Priority 0
Designated Root Cost 0
Designated Root Port 1/0
Root Max Age 0 sec Hello Time 0 sec Forward Delay 0 sec
Bridge ID MAC ADDR 00-00-00-00-00-00
Bridge ID Priority 32768
Bridge Max Age 20 sec Hello Time 2 sec Forward Delay 15 sec
Port State Role Cost Prio Type
------------------------ ------------- ---- --------- ---- ---------
cs101-hy2> (enable) sh spantree summary
Spanning tree mode: RAPID-PVST+
Runtime MAC address reduction: disabled
Configured MAC address reduction: disabled
Root switch for vlans: 483.
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.
Summary of connected spanning tree ports by vlan
VLAN Blocking Listening Learning Forwarding STP Active
----- -------- --------- -------- ---------- ----------
483 0 0 0 78 78
797 0 0 0 1 1
=======================================================================
cs101-hy2> (enable) sh spantree
VLAN 1
Spanning tree mode RAPID-PVST+
Spanning tree type ieee
Spanning tree enabled
Designated Root 00-00-00-00-00-00
Designated Root Priority 0
Designated Root Cost 0
Designated Root Port 1/0
Root Max Age 0 sec Hello Time 0 sec Forward Delay 0 sec
Bridge ID MAC ADDR 00-00-00-00-00-00
Bridge ID Priority 32768
Bridge Max Age 20 sec Hello Time 2 sec Forward Delay 15 sec
Port State Role Cost Prio Type
#vlan parameters
set spantree priority 10 497
set spantree priority 10 797
------------------------ ------------- ---- --------- ---- -----------
cs101-hy2> (enable) sh spantree summary
Spanning tree mode: RAPID-PVST+
Runtime MAC address reduction: disabled
Configured MAC address reduction: disabled
Root switch for vlans: 483.
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.
Summary of connected spanning tree ports by vlan
VLAN Blocking Listening Learning Forwarding STP Active
----- -------- --------- -------- ---------- ----------
483 0 0 0 78 78
797 0 0 0 1 1
#vlan parameters
set spantree priority 10 483
set spantree priority 10 797
==========================================
II.
I f you observe above configs , you can see that only 483 vlan is configured in cs101-hy2 switch which is access switch. vlan 483 is not configured for any switches.we configure a seperate vlan for each access switch. On Distribution layer we dont configure L2 vlans .All these layer2 vlans are intergrated with GLBP in Distribution layer switch , where routing works.
Can u plz tell me is it the right way ,if not wht should we could have done.
Awaiting for the reply.
Regards,
Akber.
04-27-2007 05:47 AM
Hi Akber
If the priority for vlan 797 is set to 10 on both cs101 and cs401 then the lowest mac-address will decide which switch becomes root for that vlan.
If you use separate vlans on each switch how are you connecting the access-list layer switches to your distribution switches. Is it with layer 2 access ports or layer 2 trunks.
Are your layer 3 vlan interfaces created on teh distribution switches. If so i'm not sure what you mean by you don't configure L2 vlans on the distribution switches.
Could you give a bit more detail.
Jon
04-27-2007 06:04 AM
Hello Jon,
I.
If you look at my above config details in bridge id mac address as 00-00-00-00-00-00 in both switches.
If that is not the right input,can u let know the command on catos to check the mac.
II. We use GLBP on Distribution switches in which you input vlan 483.
please see the below config on cr3-hy2 (Dist switch).
interface GigabitEthernet3/1
description cs101-hy2 ge1/1
ip address 155.145.183.3 255.255.255.0
ip helper-address 155.145.184.17
ip helper-address 155.145.184.14
no ip redirects
ip pim query-interval 3
ip pim sparse-mode
load-interval 30
storm-control broadcast level 0.35
glbp 483 ip 155.145.183.1
glbp 483 timers 1 3
glbp 483 timers redirect 1200 43200
glbp 483 weighting 110 lower 95 upper 105
glbp 483 load-balancing weighted
glbp 483 weighting track 1
glbp 483 weighting track 2
And Ospf routing is configured on dist switch which will communicate to core network.
~Akber.
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