Hi,
I have deployed the network topology showed below and I was surprised after found out that there isn't Backup ports. I am concern because the RSP role of ports are: Root Port, Designated Port, Alternative Port, Backup Port. After read all INE documentations I understood that AP is the alternative path to reach the Root Bridge;therefore only should be one unique AP each switch. I For example on CCIE2 Switch the RP is Fa0/23 and the Fa0/24 would be the unique Alternative Port.
I attach the outputs:
CCIE1
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 32788
Address 001c.b02f.8f00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 001c.b02f.8f00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/19 Desg FWD 19 128.19 P2p
Gi1/0/20 Desg FWD 19 128.20 P2p
Gi1/0/21 Desg FWD 4 128.21 P2p
Gi1/0/22 Desg FWD 4 128.22 P2p
Gi1/0/23 Desg FWD 19 128.23 P2p
Gi1/0/24 Desg FWD 19 128.24 P2p
CCIE2#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 32788
Address 001c.b02f.8f00
Cost 19
Port 25 (FastEthernet0/23)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 0024.5124.3880
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19 Altn BLK 19 128.21 P2p
Fa0/20 Altn BLK 19 128.22 P2p
Fa0/21 Altn BLK 19 128.23 P2p
Fa0/22 Altn BLK 19 128.24 P2p
Fa0/23 Root FWD 19 128.25 P2p
Fa0/24 Altn BLK 19 128.26 P2p
CCIE3#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 32788
Address 001c.b02f.8f00
Cost 19
Port 21 (FastEthernet0/19)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 0024.14e1.4d80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Fa0/19 Root FWD 19 128.21 P2p
Fa0/20 Altn BLK 19 128.22 P2p
Fa0/21 Desg FWD 19 128.23 P2p
Fa0/22 Desg FWD 19 128.24 P2p
Fa0/23 Altn BLK 19 128.25 P2p
Fa0/24 Altn BLK 19 128.26 P2p
CCIE4#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol rstp
Root ID Priority 32788
Address 001c.b02f.8f00
Cost 4
Port 21 (GigabitEthernet1/0/21)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address c84c.75d0.9780
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Interface Role Sts Cost Prio.Nbr Type
------------------- ---- --- --------- -------- --------------------------------
Gi1/0/19 Desg FWD 19 128.19 P2p
Gi1/0/20 Desg FWD 19 128.20 P2p
Gi1/0/21 Root FWD 4 128.21 P2p
Gi1/0/22 Altn BLK 4 128.22 P2p
Gi1/0/23 Desg FWD 19 128.23 P2p
Gi1/0/24 Desg FWD 19 128.24 P2p
