Siemens S223, S323 user manual Restarting Protocol Migration, Root Guard Configuration

User Manual	UMN:CLI
SURPASS hiD 6615 S223/S323 R1.5

8.3.7Root Guard

The standard STP does not allow the administrator to enforce the position of the root bridge, as any bridge in the network with lower bridge ID will take the role of the root bridge. Root guard feature is designed to provide a way to enforce the root bridge place- ment in the network. Even if the administrator sets the root bridge priority to zero in an ef- fort to secure the root bridge position, there is still no guarantee against bridge with prior- ity zero and a lower MAC address.

Service provider Customer

	Switch A	Switch B
Root Switch	Root Guard
	Configuration
Fig. 8.25 Root Guard

Software-based bridge applications launched on PCs or other switches connected by a customer to a service-provider network can be elected as root switches. If the priority of bridge B is zero or any value lower than that of the root bridge, device B will be elected as a root bridge for this VLAN. As a result, network topology could be changed. This may lead to sub-optimal switching. But, by configuring root guard on switch A, no switches be- hind the port connecting to switch A can be elected as a root for the service provider’s switch network. In which case, switch A will block the port connecting switch B.

To configure Root-Guard, use the following command.

Command Mode Description

stp pvst root-guard

Configures Root Guard on PVST network.

VLAN-RANGE PORTS

stp mst root-guard

Configures Root Guard on MST network.

MSTID-RANGE PORTS

Bridge

no stp pvst root-guard

VLAN-RANGE PORTS

Disables Root Guard.

no stp mst root-guard

MSTID-RANGE PORTS

8.3.8Restarting Protocol Migration

There are two switches which configured as STP and RSTP. Usually, in this case, STP protocol is used between two switches. But if someone configures the STP switch to RSTP mode, what happens? Because the RSTP switch already received STP protocol packet, the two switches still can work with STP mode even though RSTP is enabled at both. If you enable this command, the switch checks STP protocol packet once again.

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