Solved: show spanning-tree vlan id output

sarahr202 · ‎07-14-2009

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!

Jon Marshall · ‎07-14-2009

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 -

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094641.shtml#uplink_fast_theory

Cisco enhancements to 802.1d eg. portfast, uplinkfast, backbonefast were incorporated into RSTP.

Jon

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Giuseppe Larosa · ‎07-15-2009

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

View solution in original post

Giuseppe Larosa · ‎07-15-2009

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

View solution in original post

Jon Marshall · ‎07-14-2009

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 -

http://www.cisco.com/en/US/tech/tk389/tk621/technologies_tech_note09186a0080094641.shtml#uplink_fast_theory

Cisco enhancements to 802.1d eg. portfast, uplinkfast, backbonefast were incorporated into RSTP.

Jon

sarahr202 · ‎07-15-2009

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.

Giuseppe Larosa · ‎07-15-2009

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

sarahr202 · ‎07-15-2009

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.

Giuseppe Larosa · ‎07-15-2009

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

sarahr202 · ‎07-16-2009

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!

sarahr202 · ‎07-16-2009

Thanks Giuseppe!

please disregard my last post. i got my answer when i re-read your post.

thanks and have a nice day!