Enabling and configuring RSTP on an interface

Follow these steps to configure RSTP on an Ethernet interface.

You can configure the parameters individually on an interface by doing the following:

Entering the commands in Steps 1 through 3.
Specifying additional parameters, as appropriate.
Verifying the result.
Saving the configuration.

For detailed descriptions of the parameters and features, see the sections STP parameters and STP features.

Enter global configuration mode.
```
device# configure terminal
```
Enter interface subtype configuration mode.
```
device(config)# interface ethernet 0/10
```
Enable the interface.
```
device(conf-if-eth-0/10)# no shutdown
```
To disable the spanning tree on the interface you use the spanning-tree shutdown command.
Specify the port priority on the interface.
```
device(conf-if-eth-0/10)# spanning-tree priority 128
```
The range is from 0 through 240 in increments of 16. The default value is 128.
Specify the path cost on the interface.
```
device(conf-if-eth-0/10)# spanning-tree cost 20000000
```
The lower the path cost means a greater chance that the interface becomes the root port. The range is 1 through 200000000. The default path cost is assigned as per the port speed.
Enable edge port.
```
device(conf-if-eth-0/10)# spanning-tree edgeport
```
If BPDUs are received on a port fast enabled interface, the interface loses the edge port status unless it receives a shutdown or no shutdown command.
Enable BPDU guard on the interface.
```
device(conf-if-eth-0/10)# spanning-tree edgeport bpdu-guard
```
BPDU guard removes a node that reflects BPDUs back in the network. It enforces the STP domain borders and keeps the active topology predictable by not allowing any network devices behind a BPDU guard-enabled port to participate in STP.
Enable automatic edge detection on the interface.
```
device(conf-if-eth-0/10)# spanning-tree autoedge
```
You use this command to automatically identify the edge port. A port becomes an edge port if it receives no BPDUs. By default, automatic edge detection is disabled.
Enable root guard on the interface.
```
device(conf-if-eth-0/10)# spanning-tree guard root
```
Root guard protects the root bridge from malicious attacks and unintentional misconfigurations where a bridge device that is not intended to be the root bridge becomes the root bridge.
Specify a link type on the interface.
```
device(conf-if-eth-0/10)# spanning-tree link-type point-to-point
```
Note
The link type is explicitly configured as point-to-point rather than shared.
Return to privileged EXEC mode.
```
device(conf-if-eth-0/10)# end
```

Verify the configuration.

device# show spanning-tree 

 Spanning-tree Mode: Rapid Spanning Tree Protocol

 Root Id: 8000.01e0.5200.0180 (self)
 Bridge Id: 8000.01e0.5200.0180

 Root Bridge Forward Delay: 15; Hello Time: 2; Max Age: 20; Max-hops: 20
 Configured Forward Delay: 15; Hello Time: 2; Max Age: 20; Max-hops: 20
 Number of topology change(s): 0

 Bpdu-guard errdisable timeout: enabled
 Bpdu-guard errdisable timeout interval: 60 sec


 Port Eth 0/10 enabled
    Ifindex: 201359360; Id: 8002; Role: Disabled; State: Disabled
    Designated Path Cost: 0
    Configured Path Cost: 20000000
    Designated Port Id: 0; Port Priority: 128
    Designated Bridge: 0000.0000.0000.0000
    Number of forward-transitions: 0
    Version: Spanning Tree Protocol - Received None - Sent STP
    Edgeport: on; AutoEdge: yes; AdminEdge: no; EdgeDelay: 3 sec
    Configured Root guard: on; Operational Root guard: on
    Bpdu-guard: on
    Link-type: point-to-point
    Received BPDUs: 0; Sent BPDUs: 0 

Interface   Role     Sts     Cost       Prio     Link-type     Edge
---------------------------------------------------------------------
Eth 0/10    DES      FWD     20000000   128      P2P           No

The forward-delay, hello-time, and max-age parameters are set globally, not on the interface.

Observe that the settings comply with the formula set out in the STP parameters section, as:

(2 × (forward delay - 1)) ≥ maximum age ≥ (2 × (hello time + 1))

or in this case: 28 ≥ 20 ≥ 6.

Save the configuration.

device# copy running-config startup-config

RSTP on an interface configuration example

device# configure terminal
device(config)# interface ethernet 0/10
device(conf-if-eth-0/10)# no spanning-tree shutdown
device(conf-if-eth-0/10)# spanning-tree priority 128
device(conf-if-eth-0/10)# spanning-tree cost 20000000
device(conf-if-eth-0/10)# spanning-tree edgeport
device(conf-if-eth-0/10)# spanning-tree edgeport bpdu-guard
device(conf-if-eth-0/10)# spanning-tree autoedge
device(conf-if-eth-0/10)# spanning-tree guard root
device(conf-if-eth-0/10)# spanning-tree link-type point-to-point
device(conf-if-eth-0/10)# end
device# show spanning-tree 
device# copy running-config startup-config