07-16-2010 06:47 PM - edited 03-06-2019 12:03 PM
Hi Everybody,
There was a question about identifying the root switch in a layer 2 network from a non-root switch on a CCNA exam simulator. I would like to know if there is a command on a switch that could identify the root hostname or if the only way to identify a root switch on a CCNA simulator is to identify the neighbors with show CDP neighbor, telnet to the neighbors and look for the root switch with show spanning-tree vlan 1.
Thanks for your help
Stephane
07-16-2010 11:50 PM
sh spanning-tree summary
07-17-2010 01:14 AM
Hi Everybody,
There was a question about identifying the root switch in a layer 2 network from a non-root switch on a CCNA exam simulator. I would like to know if there is a command on a switch that could identify the root hostname or if the only way to identify a root switch on a CCNA simulator is to identify the neighbors with show CDP neighbor, telnet to the neighbors and look for the root switch with show spanning-tree vlan 1.
Thanks for your help
Stephane
Hi Stephane,
Show spanning-tree root would be the best to just find the root, but it doesn't give you all the extra info you get from the show spanning-tree command.
Switch#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 001e.f6d6.e400
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 001e.f6d6.e400
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Po1 Desg FWD 3 128.56 P2p
Hope to Help !!
Ganesh.H
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07-17-2010 05:51 AM
Hello Stephane,
>> r is to identify the neighbors with show CDP neighbor, telnet to the neighbors and look for the root switch with show spanning-tree vlan 1
if you look at the show spanning-tree vlan 1 in Ganesh's post you can see that the root bridge is identified by its MAC address.
the show spanning-tree provides you also the root port that is the port on the best path to the root, following the root ports of switches between the first one and the root bridge you can find it.
Actually, CDP is of great help in identifying the neighobor switch connected to the root port.
The root switch hostname is not available as STP lies in OSI layer2 and the hostname is linked in DNS with an IP address (OSI layer3)
Hope to help
Giuseppe
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