07-14-2009 10:19 AM - edited 03-06-2019 06:45 AM
Hi every body!
I have two book both show different output for the same command( show spanning-tree vlan id)for a switch running stp.
One output shows the following ( output omitted)
sw# show spanning-tree vlan 3
spanning-tree enabled protocol ieee
( output omitted)
int role stat cost pri.nbr type
f0/1 atln blk 19 128.11 p2p
==============================
My book says" While the atlernate port role is an RSTP concept, the cisco 802.1d implementation also uses this concept"
=========================================
My other book shows the output for " show spanning-tree vlan id" command differently though switch is running stp.
I omitted the output only showing the difference.
sw# show spanning-tree vlan 4
spanning-tree enabled prtocol ieee.
out put omitted
int port id prio cost sts designated etc
fo1 128.1 128 19 fwd
Here the role such as atlernate, root, desg are not shown though switch is running stp.
=============================
thanks a lot and have a good day!
Solved! Go to Solution.
07-14-2009 08:28 PM
Sarah
The first ouput looks like the output of STP on a switch using RPVST+.
The second output looks like the output of STP on a switch using PVST+.
As for the alternate port Cisco used this in the uplinkfast feature which was an enhancement to 802.1d. Note that uplinkfast was Cisco proprietary, more details of uplinkfast here -
Cisco enhancements to 802.1d eg. portfast, uplinkfast, backbonefast were incorporated into RSTP.
Jon
07-15-2009 07:29 AM
Hello Sarah,
good note as usual
In another thread Francois Tallet has explained that Cisco had unified the show output, and they show alternate state now even if formally it is not defined in 802.1d legacy.
In other words the show doesn't change the fileds names with STP mode from PVST+ to RPVST
See this example taken from a switch running PVST+ (not rapid)
sh spanning-tree vlan 904
VLAN0904
Spanning tree enabled protocol ieee
Root ID Priority 0
Address 00d0.031a.0788
Cost 3003
Port 646 (Port-channel6)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 50056 (priority 49152 sys-id-ext 904)
Address 0022.55be.4740
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Uplinkfast enabled
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi6/21 Desg FWD 3004 128.341 P2p
Gi7/32 Desg FWD 3004 128.416 P2p
Po4 Desg FWD 3003 128.644 P2p
Po5 Altn BLK 3003 128.645 P2p
Po6 Root FWD 3003 128.646 P2p
Po8 Desg FWD 3003 128.648 P2p
as you can see there are designated ports as well root port and alternate port here uplink fast is enabled.
Hope to help
Giuseppe
07-15-2009 10:45 PM
Hello Sarah,
>> How can we tell by looking at output if uplink fast is enabled.
there is a line in output of my example that tells Uplinkfast is enabled
However, I agree with Jon's explanation an alternate state implies uplinkfast in legacy STP 802.1D
Hope to help
Giuseppe
07-14-2009 08:28 PM
Sarah
The first ouput looks like the output of STP on a switch using RPVST+.
The second output looks like the output of STP on a switch using PVST+.
As for the alternate port Cisco used this in the uplinkfast feature which was an enhancement to 802.1d. Note that uplinkfast was Cisco proprietary, more details of uplinkfast here -
Cisco enhancements to 802.1d eg. portfast, uplinkfast, backbonefast were incorporated into RSTP.
Jon
07-15-2009 07:14 AM
thanks Jon.
But in the first output , it says " stp protocol ieee is enabled. Then the book explains the out put by sying though alternate port is rstp concept,cisco 802.1q implementation uses this role as well.
07-15-2009 07:29 AM
Hello Sarah,
good note as usual
In another thread Francois Tallet has explained that Cisco had unified the show output, and they show alternate state now even if formally it is not defined in 802.1d legacy.
In other words the show doesn't change the fileds names with STP mode from PVST+ to RPVST
See this example taken from a switch running PVST+ (not rapid)
sh spanning-tree vlan 904
VLAN0904
Spanning tree enabled protocol ieee
Root ID Priority 0
Address 00d0.031a.0788
Cost 3003
Port 646 (Port-channel6)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 50056 (priority 49152 sys-id-ext 904)
Address 0022.55be.4740
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Uplinkfast enabled
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi6/21 Desg FWD 3004 128.341 P2p
Gi7/32 Desg FWD 3004 128.416 P2p
Po4 Desg FWD 3003 128.644 P2p
Po5 Altn BLK 3003 128.645 P2p
Po6 Root FWD 3003 128.646 P2p
Po8 Desg FWD 3003 128.648 P2p
as you can see there are designated ports as well root port and alternate port here uplink fast is enabled.
Hope to help
Giuseppe
07-15-2009 01:05 PM
Thanks Giuseppe!
How can we tell by looking at output if uplink fast is enabled.
It is because " altn blk" field cisco used to indicate uplink fast feature as Jon mentioned in his response.
07-15-2009 10:45 PM
Hello Sarah,
>> How can we tell by looking at output if uplink fast is enabled.
there is a line in output of my example that tells Uplinkfast is enabled
However, I agree with Jon's explanation an alternate state implies uplinkfast in legacy STP 802.1D
Hope to help
Giuseppe
07-16-2009 06:27 AM
Thanks Giuseppe!
Since uplink is optional feature,therefore it will only show up as "alternate" in the output of show spanning-tree vlan id if uplink feature is coonfigured. is it correct ?
thanks and have a nice a day!
07-16-2009 08:35 AM
Thanks Giuseppe!
please disregard my last post. i got my answer when i re-read your post.
thanks and have a nice day!
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