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Home > Archive > CCNA > October 2002 > spanning tree
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| dasaint 2002-10-22, 11:42 am |
| hello guys
ever encountered this question
" you issued the show spantree e0/1 command which part of the output indicates that virtual LAN1 is functioning properly"
i have seen two different answers from diff cheetsheets
a) VLAN is executing the IEEE compatible spanning tree protocol
b) port ethernet 0/1 of VLAN is forwarding
so as you can guess i am sort of confused, does any one know the right answer | |
| drdirt 2002-10-22, 3:37 pm |
| DaSaint:
I will try to answer this from testing the question on a real router lab - but, I don't know much about this subject, unlike many of the regular responses here...
In the output to the "show spantree e0/1"
you will see both statements.
a) (actual output) "VLAN1 is executing the IEEE compatible Spanning-Tree Protocol"
means that it is configured and running. It doesn't really indicate that it is running properly.
b) "Port Ethernet 0/1 of VLAN1 is Forwarding" means, at least, that the STP has converged and one port is forwarding, some presumably blocking.
It is no guarantee that there are no errors, but b) seems to indicate that at least some of the STP is functioning. The Root Bridge has been identified and is forwarding.
So b) would be the best answer.
Anybody shed more light on this??? | |
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| edmonds_robert 2002-10-23, 8:56 am |
| Actually most IOS based switches use the same format to identify ports nowadays. For example, here is the actual from one of my many 3500 series IOS based switches:
SWITCH#sh spanning-tree int fa0/1
Interface Fa0/1 (port 13) in Spanning tree 39 is FORWARDING
Port path cost 19, Port priority 128
Designated root has priority 8192, address 0004.6d85.7826
Designated bridge has priority 32768, address 0030.852a.f312
Designated port is 13, path cost 19
Timers: message age 0, forward delay 0, hold 0
BPDU: sent 8373495, received 0
The port is in the portfast mode
Notice the format of fa0/1, or mod#/port#. | |
| dasaint 2002-10-23, 9:27 am |
| thanks for the discussion on mod#/port# , but please can you guys please address the issue of which output indicates spanning tree is functioning properly
thanks | |
| edmonds_robert 2002-10-23, 9:52 am |
| I would agree with ddirt. Among the answers given, B would be the best.
However, in practice, most of the information contained in the output would be useful for troubleshooting. For example, notice the line that reads, "Designated root has priority 8192, address 0004.6d85.7826". On my network, I know the only bridge that has a priority of 8192 is the root bridge, which I have configured manually to be such. That and the MAC address tell me that it is seeing the correct bridge as the root. Also, since this port is an access port with portfast enabled, forwarding is the only state it should be in, so that's good too. | |
| drdirt 2002-10-24, 1:12 am |
| Thanks Robert,
I think you gave us newbies a couple unasked for tips -
Note how he assigns priority to be sure which is elected the root bridge. Not only did he choose a fast port (this would probably happen anyway, wouldn't it?)
BUT - when troubleshooting, you know immediately if the first-choice root bridge is down and that something is wrong.
Simple, should be obvious - but it hadn't occurred to me -
I like it. | |
| guitarjim 2002-10-24, 8:42 am |
| Thanks for the update. I took a look at the many parameters available for your switch at:
http://www.cisco.com/univercd/cc/td.../cli2.htm#47293
In the output shown,
Interface Fa0/1 (port 13) in Spanning tree 39 is FORWARDING
Does spanning tree 39 = vlan 39?
Note: PortFast mode is used only for a port connected to a single host ie: workstation or server. It doesn't need to be part of the stp decision making process. It always forwards. Never use if port is a redundant link. | |
| edmonds_robert 2002-10-24, 11:34 am |
| Spanning tree 39 does indeed mean VLAN 39. | |
| bfattima 2002-10-25, 8:52 am |
| quote:
Originally posted by drdirt
DaSaint:
I will try to answer this from testing the question on a real router lab - but, I don't know much about this subject, unlike many of the regular responses here...
In the output to the "show spantree e0/1"
you will see both statements.
a) (actual output) "VLAN1 is executing the IEEE compatible Spanning-Tree Protocol"
means that it is configured and running. It doesn't really indicate that it is running properly.
b) "Port Ethernet 0/1 of VLAN1 is Forwarding" means, at least, that the STP has converged and one port is forwarding, some presumably blocking.
It is no guarantee that there are no errors, but b) seems to indicate that at least some of the STP is functioning. The Root Bridge has been identified and is forwarding.
So b) would be the best answer.
Anybody shed more light on this???
I read the same quetion, but difereent practice exam gave me different answers, B and A and I believe it's a real exam question can someone give us the correct answers
thank you all | |
| duanesnyder 2002-10-26, 11:12 am |
| So far I have had this question twice in the Cisco practice tests, (I am on chapter 9 semester 4) and the answer Cisco is looking for is B !! every time. |
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