Enhancement in STP
Port fast, Uplink fast and Backbonefast
Port Fast :- Port fast is a feature which will make a switchport comes directly in the Forwarding state instead of waiting 50 sec and processing every state of (Blocking,Listining,Learning) before coming in the
forwarding state. Recomended to enable on the Access ports only.
sw(config)#spanning-tree portfast
Uplink Fast :- suppose When a switch has two paths to reach the root bridge then by default one of the uplink will be disabled by the STP, and if the active uplink goes down then the secondary link will take 60 sec to comes in the active state and we cannot run portfast in this situation, so to reduce this we use uplink fast. uplink fast feature is enabled globally not on the port basis as portfast
sw(config)# spanning-tree uplinkfast
Backbone fast :- Backbone fast feature is used for indirect link failures to the root bridge/switch. Backbone fast feature uses the Root link query protocol to detect indirect link failures. Backbone fast feature is enabled globally and has to be enable on all the switches in the network.
Backbone-fast applies when the switch receives an inferior BPDU. An inferior BPDU is a BPDU that is received by the secondary root switch telling that it is the actual root switch.
The secondary root switch denies that and sends the actual root switch path to the inferior switch.
sw(config)#spanning-tree backbonefast
Per-VLAN STP
STP doesn't guarantee an optimized loop-free network. PVST supports one instance of STP per VLAN.
Lab on PVST
do this on SW1, SW2 as in SW0
SW0(config)#int range fa0/1 - 2
SW0(config-if-range)#switchport mode trunk
SW0(config)#vlan 10
SW0(config-vlan)#vlan 20
now on SW0 run these commands:
SW0(config)#spanning-tree vlan 10 root primary
SW0(config)#spanning-tree vlan 20 root secondary
now move to SW2 and fire following commands:
SW2(config)#spanning-tree vlan 10 root secondary
SW2(config)#spanning-tree vlan 20 root primary
check the output on SW0 & SW2
SW0#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0050.0FBE.28E6
Cost 19
Port 2(FastEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Root FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 24586
Address 0060.3E0B.8459
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Desg FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 0050.0FBE.28E6
Cost 19
Port 2(FastEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28692 (priority 28672 sys-id-ext 20)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Root FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
Yep this is root for vlan 10
Now output at SW2
SW2#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0050.0FBE.28E6
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 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 24586
Address 0060.3E0B.8459
Cost 19
Port 1(FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28682 (priority 28672 sys-id-ext 10)
Address 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 0050.0FBE.28E6
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24596 (priority 24576 sys-id-ext 20)
Address 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
Yep this is root for vlan 20.
Port fast, Uplink fast and Backbonefast
Port Fast :- Port fast is a feature which will make a switchport comes directly in the Forwarding state instead of waiting 50 sec and processing every state of (Blocking,Listining,Learning) before coming in the
forwarding state. Recomended to enable on the Access ports only.
sw(config)#spanning-tree portfast
Uplink Fast :- suppose When a switch has two paths to reach the root bridge then by default one of the uplink will be disabled by the STP, and if the active uplink goes down then the secondary link will take 60 sec to comes in the active state and we cannot run portfast in this situation, so to reduce this we use uplink fast. uplink fast feature is enabled globally not on the port basis as portfast
sw(config)# spanning-tree uplinkfast
Backbone fast :- Backbone fast feature is used for indirect link failures to the root bridge/switch. Backbone fast feature uses the Root link query protocol to detect indirect link failures. Backbone fast feature is enabled globally and has to be enable on all the switches in the network.
Backbone-fast applies when the switch receives an inferior BPDU. An inferior BPDU is a BPDU that is received by the secondary root switch telling that it is the actual root switch.
The secondary root switch denies that and sends the actual root switch path to the inferior switch.
sw(config)#spanning-tree backbonefast
Per-VLAN STP
STP doesn't guarantee an optimized loop-free network. PVST supports one instance of STP per VLAN.
Lab on PVST
do this on SW1, SW2 as in SW0
SW0(config)#int range fa0/1 - 2
SW0(config-if-range)#switchport mode trunk
SW0(config)#vlan 10
SW0(config-vlan)#vlan 20
now on SW0 run these commands:
SW0(config)#spanning-tree vlan 10 root primary
SW0(config)#spanning-tree vlan 20 root secondary
now move to SW2 and fire following commands:
SW2(config)#spanning-tree vlan 10 root secondary
SW2(config)#spanning-tree vlan 20 root primary
check the output on SW0 & SW2
SW0#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0050.0FBE.28E6
Cost 19
Port 2(FastEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Root FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 24586
Address 0060.3E0B.8459
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24586 (priority 24576 sys-id-ext 10)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Desg FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 0050.0FBE.28E6
Cost 19
Port 2(FastEthernet0/2)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28692 (priority 28672 sys-id-ext 20)
Address 0060.3E0B.8459
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/2 Root FWD 19 128.2 P2p
Fa0/1 Desg FWD 19 128.1 P2p
Yep this is root for vlan 10
Now output at SW2
SW2#sh spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 0050.0FBE.28E6
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 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
VLAN0010
Spanning tree enabled protocol ieee
Root ID Priority 24586
Address 0060.3E0B.8459
Cost 19
Port 1(FastEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28682 (priority 28672 sys-id-ext 10)
Address 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Root FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 0050.0FBE.28E6
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24596 (priority 24576 sys-id-ext 20)
Address 0050.0FBE.28E6
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p
Yep this is root for vlan 20.
Rapid Spanning Tree Protocol
The 802.1d standard was designed back when waiting for 30 to 50 seconds for layer 2 convergence wasn’t a problem. However, in today’s networks, this can cause serious performance problems for networks that use real-time applications, such as voice over IP (VoIP) or video.
The Rapid Spanning Tree Protocol (RSTP) is an IEEE standard, defined in 802.1w, which is interoperable with 802.1d and an extension to it. With RSTP, there are only three port states:
discarding (it is basically the grouping of 802.1d’s blocking, listening, and disabled states).
Learning
Forwarding
Additional Port Roles
With RSTP, there is still a root switch and there are still root and designated ports, performing the same roles as those in 802.1d. However, RSTP adds two additional port types: alternate ports and backup ports.
These two ports are similar to the ports in a blocking state in 802.1d.
An alternate port is a port that has an alternative path or paths to the root but is currently in a discarding state.
A backup port is a port on a segment that could be used to reach the root switch, but an active port is already designated for the segment.
The best way to look at this is that an alternate port is a secondary, unused root port, and a backup port is a secondary, unused designated port.
RSTP BPDUs
With 802.1w, if a BPDU is not received in three expected hello periods (6 seconds), STP information can be aged out instantly and the switch considers that its neighbor is lost and actions should be taken. This is different from 802.1d, where the switch had to miss the BPDUs from the root—here, if the switch misses three consecutive hellos from a neighbor, actions are immediately taken.
Lab on RSTP
on each & every switch enable rapid-pvst
SW0(config)#spanning-tree mode rapid-pvst
then on switch SW1 & SW2 run
SW1(config-if)#switchport mode access
SW1(config-if)#spanning-tree portfast
and you can verify your configuration
SW2#show spanning-tree
VLAN0001
Spanning tree enabled protocol rstp
Root ID Priority 32769
Address 0001.C915.C4CA
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 0001.C915.C4CA
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 20
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/3 Desg FWD 19 128.3 P2p
Fa0/1 Desg FWD 19 128.1 P2p
Fa0/2 Desg FWD 19 128.2 P2p\
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