Configuring Rapid Spanning Tree Protocol (RSTP)


Rapid Spanning Tree Protocol (RSTP), a standard inter-switch protocol, ensures an ad hoc network topology loop-free at Layer 2, on a per-VLAN basis. If your network connections form loops and you disable STP, packets re-circulate between the switches, causing a degradation of network performance. STP does not allow for Layer 2 multipathing and can result in sub-optimal utilization of available network links. Therefore, a fabric of switches does not run RSTP within the boundaries of the fabric. Pluribus Networks recommends the use of RSTP for ad hoc networks that inter-operate in a heterogeneous, multi-vendor switch environment.To build a loop-free topology, switches (“bridges”) determine the root bridge and compute the port roles, root, designated, or blocked.


To do this, the bridges use special data frames called Bridge Protocol Data Units (BPDUs) to exchange information about bridge IDs and root path costs. BPDUs exchange regularly, typically at two second intervals, and enable switches to keep track of network topology changes and to start and stop forwarding on ports as required. Hosts should not send BPDUs to the switch ports and to avoid malfunctioning or malicious hosts from doing so, the switch can filter or block BPDUs. If you enable BPDU filtering on a port, BPDUs received on that port drop but other network traffic forwards as usual.  If you enable BPDU blocking on a port, BPDUs received on that port are dropped and the port is shut down.

 

Rapid Spanning Tree Protocol is also supported by modifying an RSTP port and configuring it as an edge port.


Note: RSTP is enabled on the switch by default.


Before you begin, view the status of STP on the switch by using the following command:


CLI (network-admin@Leaf1) > stp-show


switch:             tac-1

enable:             yes

stp-mode:           rstp

bpdus-bridge-ports: yes

bridge-id:          3a:7f:b1:43:8a:0f

bridge-priority:    32768

hello-time:         2

forwarding-delay:   15

max-age:            20

cluster-mode:       master

 

 

To disable STP, use the following command:


CLI (network-admin@Leaf1) > stp-modify disable


To display the STP state, use the following command:


CLI (network-admin@Leaf1) > stp-state-show


switch:           Leaf01

vlan:             1

ports:            none

instance-id:      1

name:             stg-default

bridge-id:        66:0e:94:65:e1:ef

bridge-priority:  8193

root-id:          64:0e:94:c0:06:4b

root-priority:    4097

root-port:        128

hello-time:       2

forwarding-delay: 15

max-age:          20

disabled:         none

learning:         none

forwarding:       25-28,128-129

discarding:       none

edge:             25-28

designated:       25-28,129

alternate:        none

backup:           none

 

To display information about STP on ports, use the stp-port-show command:


CLI (network-admin@Leaf1) > stp-port-show


switch port block filter edge bpdu-guard root-guard priority cost

------ ---- ----- ------ ---- ---------- ---------- -------- ----

Leaf1   1    off   off    no    no         no        128      500  

Leaf1   2    off   off    no    no         no        128      2000

Leaf1   3    off   off    no    no         no        128      2000

Leaf1   4    off   off    no    no         no        128      2000

Leaf1   5    off   off    no    no         no        128      500  

Leaf1   6    off   off    no    no         no        128      500  

Leaf1   7    off   off    no    no         no        128      2000

Leaf1   8    off   off    no    no         no        128      2000

Leaf1   9    off   off    no    no         no        128      2000

Leaf1   10   off   off    no    no         no        128      500

 

To filter BPDUs on port 17, use the following command:


CLI (network-admin@Leaf1) > stp-port-modify port 17 filter


To block BPDUs on port 17 and shut down the port if BPDUs are received on the port, use the following command:


CLI (network-admin@Leaf1) > stp-port-modify port 17 block


To stop blocking BPDUs on port 17, use the following command:


CLI (network-admin@Leaf1) > stp-port-modify port 17 no-block


You can disable STP on a port or a group of ports. If the devices connected to the switch ports are hosts and not downstream switches, or you know that a loop is not possible, then disable STP and the port is enabled much faster when the switch restarts.

To enable RSTP on port 35, use the following command:


CLI (network-admin@Leaf1) > stp-port-modify port 35 edge


To enable STP, use the following command:


CLI (network-admin@Leaf1) > stp-modify enable