Root port selection

gregorydhenderson1 · ‎09-02-2015

Using the topology above: ALS2 is actually a 2960-s (Gig ports). DLS2 is a 3550. 802.1q configured on all links.

Gi1/0/9 is selected as the RP but I don't understand why. DLS2 is the Root Bridge and I was expecting Gi1/0/7 or 8 to be RP.

Here is my show spanning tree for this :

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        9 (GigabitEthernet1/0/9)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     7c95.f32d.f880
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/7             Altn BLK 2         128.7    P2p
Gi1/0/8             Altn BLK 19        128.8    P2p
Gi1/0/9             Root FWD 19        128.9    P2p
Gi1/0/10            Altn BLK 19        128.10   P2p
Gi1/0/11            Altn BLK 19        128.11   P2p Peer(STP)
Gi1/0/12            Altn BLK 19        128.12   P2p Peer(STP)

I just changed the cost on Gi1/0/7 to see if that would change it but it did not. The speed of the links are all the same, so I thought adjusting the cost would make a difference. To me, the port priority of gi1/0/7 should make it the root port if nothing else since it is lower. I'm confused on this one and I have a good grasp on STP. All switches running RPVST and only VLAN 1 is active. Any help would be appreciated.

gregorydhenderson1 · ‎09-02-2015

Please excuse my typo RSTP is running not RPVST.

Jon Marshall · ‎09-02-2015

Can you post the same outputs from DLS1 and DLS2 ?

Jon

gregorydhenderson1 · ‎09-02-2015

DLS1#show spanning-tree

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        13 (FastEthernet1/0/11)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     0019.e706.5500
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/7             Desg FWD 19        128.9    P2p
Fa1/0/8             Desg FWD 19        128.10   P2p
Fa1/0/9             Desg FWD 19        128.11   P2p Peer(STP)
Fa1/0/10            Desg FWD 19        128.12   P2p Peer(STP)
Fa1/0/11            Root FWD 19        128.13   P2p
Fa1/0/12            Altn BLK 19        128.14   P2p

DLS2#sh sp
DLS2#sh spanning-tree

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             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     0011.2109.5a00
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p Peer(STP)
Fa0/8               Desg FWD 19        128.8    P2p Peer(STP)
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/10              Desg FWD 19        128.10   P2p
Fa0/11              Desg FWD 19        128.11   P2p
Fa0/12              Desg FWD 19        128.12   P2p

gregorydhenderson1 · ‎09-02-2015

ALS22960#sho sp

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        9 (GigabitEthernet1/0/9)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     7c95.f32d.f880
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/7             Altn BLK 16         64.7    P2p
Gi1/0/8             Altn BLK 19        128.8    P2p
Gi1/0/9             Root FWD 19        128.9    P2p
Gi1/0/10            Altn BLK 19        128.10   P2p
Gi1/0/11            Altn BLK 19        128.11   P2p Peer(STP)
Gi1/0/12            Altn BLK 19        128.12   P2p Peer(STP)

Jon Marshall · ‎09-02-2015

What models are all the switches ?

I think the issue is that some of the switches think other switches are running PVST ie. "P2p Peer(STP)" in your outputs.

Jon

gregorydhenderson1 · ‎09-02-2015

DLS1 -- 3750

DLS2 - 3550

ALS1 -2950

ALS2 -2960

Jon Marshall · ‎09-02-2015

Can you post the same output from the other access switch ?

Is this a lab setup ?

Jon

gregorydhenderson1 · ‎09-02-2015

Yes, this is a lab environment.

ALS12950#sh spanning-tree

VLAN0001
Spanning tree enabled protocol ieee
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        7 (FastEthernet0/7)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     001a.a1ad.d980
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/7            Root FWD 19        128.7    P2p
Fa0/8            Altn BLK 19        128.8    P2p
Fa0/9            Altn BLK 19        128.9    P2p
Fa0/10           Altn BLK 19        128.10   P2p
Fa0/11           Desg FWD 19        128.11   P2p
Fa0/12           Desg FWD 19        128.12   P2p

Jon Marshall · ‎09-02-2015

This switch is not running RSTP.

Can you modify the configuration and then see what happens.

Jon

gregorydhenderson1 · ‎09-02-2015

I found that problem earlier on two other switches. I missed this one. Ill fix it now Thank you. One sec.

gregorydhenderson1 · ‎09-02-2015

Changed to RSTP but no change on ALS2. Gi1/0/9 is still RP.

Jon Marshall · ‎09-02-2015

The costs are all wrong in terms of costs.

As this is a lab can you -

1) shut all interfaces between the switches

2) bring up just one of the links between each switch and then see what they all think.

I presume now you have them all running RSTP you are not seeing those peer messages anymore ?

Jon

gregorydhenderson1 · ‎09-02-2015

You are correct. the peer messages are gone. I'll execute the steps you outlined and see what happens.

gregorydhenderson1 · ‎09-02-2015

OK, here are the results: it appears unchanged.

DLS1#sh
*Mar 1 08:26:13.580: %SYS-5-CONFIG_I: Configured from console by consolesp

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Por        13 (FastEthernet1/0/11)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     0019.e706.5500
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa1/0/7             Desg FWD 19        128.9    P2p
Fa1/0/9             Desg BLK 19        128.11   P2p
Fa1/0/11            Root FWD 19        128.13   P2p

DLS2#sh sp

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             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     0011.2109.5a00
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/7               Desg FWD 19        128.7    P2p
Fa0/9               Desg FWD 19        128.9    P2p
Fa0/11              Desg FWD 19        128.11   P2p

ALS12950#sh spanning-tree

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        7 (FastEthernet0/7)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     001a.a1ad.d980
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/7            Root FWD 19        128.7    P2p
Fa0/9            Altn BLK 19        128.9    P2p
Fa0/11           Desg FWD 19        128.11   P2p

ALS22960#sh sp

VLAN0001
Spanning tree enabled protocol rstp
Root ID    Priority    32769
             Address     0011.2109.5a00
             Cost        19
             Port        9 (GigabitEthernet1/0/9)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority    32769 (priority 32768 sys-id-ext 1)
             Address     7c95.f32d.f880
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec

Interface           Role Sts Cost      Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/7             Altn BLK 16         64.7    P2p
Gi1/0/9             Root FWD 19        128.9    P2p
Gi1/0/11            Altn BLK 19        128.11   P2p