Rapid Spanning Tree Protocol (RSTP)


The Rapid Spanning Tree Protocol (RSTP) is an optimized version of STP. RSTP allows a newly elected root port or designated port to enter the forwarding state much quicker under certain conditions than in STP, hence quicker network convergence.
Although RSTP allows quicker network convergence, it has the same drawback as STP does: All bridges within a LAN share the same spanning tree, so redundant links cannot be blocked based on VLAN and the packets of all VLANs are forwarded along the same spanning tree.

Network Diagram

Figure 1 Network diagram for RSTP configuration


Networking and Configuration Requirements

1)        Switch A at the core layer.
Configure it as the root bridge.
2)        Switch B and Switch C at the distribution layer.
l          Configure Switch C as the standby switch of Switch B. When Switch B fails, Switch C automatically takes over to forward data.
l          Configure two links between Switch C and Switch B, ensuring one link is available when the other fails.
3)        Switch D, Switch E, and Switch F at the access layer.
l          User PCs are connected to Switch D, Switch E, and Switch F.
l          Connect Switch D, Switch E, Switch F to Switch C and Switch B.
Only RSTP-related configurations are provided in the sample configuration. In addition, as the RSTP configurations on Switch D through Switch F are basically the same, only those on Switch D are provided.

Configuration Example

1)        Configuration on Switch A
#
stp mode rstp
stp instance 0 priority 0
(stp instance 0 root primary)
stp TC-protection enable
stp enable
#
interface GigabitEthernet2/0/1
 stp root-portection
#
interface GigabitEthernet2/0/2
 stp root-portection
#
interface GigabitEthernet2/0/4
 stp disable
2)        Configuration on Switch B
#
stp mode rstp
stp instance 0 priority 4096
stp enable
#
interface Ethernet1/0/4
 stp root-portection
#
interface Ethernet1/0/5
 stp root-portection
#
interface Ethernet1/0/6
 stp root-portection
#
interface Ethernet1/0/8
 stp disable
3)        Configuration on Switch C
#
stp mode rstp
stp instance 0 priority 8192
stp enable
#
interface Ethernet1/0/1
 stp root-portection
#
interface Ethernet1/0/2
 stp root-portection
#
interface Ethernet1/0/3
 stp root-portection
#
interface Ethernet1/0/8
 stp disable
4)        Configuration on Switch D
#
stp mode rstp
stp enable
#
interface Ethernet1/0/3
 stp disable
 interface Ethernet3/0/5
 stp edged-port enable
 stp bpdu-portection

Configuration Guidelines

To change the STP mode between STP, RSPT, or MSTP, use the stp mode command. By default, an MSTP-enabled device works in MSTP mode.

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