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Table 72 Advanced Application > Spanning Tree Protocol > Status: MRSTP (continued)
LABEL
Port Role
Designated Bridge
ID
Designated Port ID
Designated Cost
Root Guard State
13.10 Technical Reference
This section provides technical background information on the topics discussed in this chapter.
13.10.1 MSTP Network Example
The following figure shows a network example where two VLANs are configured on the two switches. If
the switches are using STP or RSTP, the link for VLAN 2 will be blocked as STP and RSTP allow only one link
in the network and block the redundant link.
Figure 141 STP/RSTP Network Example
Chapter 13 Spanning Tree Protocol
DESCRIPTION
This field displays the role of the port in STP.
•
Root – A forwarding port on a non-root bridge, which has the lowest path cost and is the
best port from the non-root bridge to the root bridge. A root bridge does not have a root
port.
•
Designated – A forwarding port on the designated bridge for each connected LAN
segment. A designated bridge has the lowest path cost to the root bridge among the
bridges connected to the LAN segment. All the ports on a root bridge (root switch) are
designated ports.
•
Alternate – A blocked port, which has a best alternate path to the root bridge. This path is
different from using the root port. The port moves to the forwarding state when the
designated port for the LAN segment fails.
•
Backup – A blocked port, which has a backup or redundant path to a LAN segment
where a designated port is already connected when a switch has two links to the same
LAN segment.
•
Disabled – Not strictly part of STP. The port can be disabled manually.
This field displays the identifier of the designated bridge to which this port belongs when the
port is a designated port. Otherwise, it displays the identifier of the designated bridge for the
LAN segment to which this port is connected.
This field displays the priority and number of the bridge port (on the designated bridge),
through which the designated bridge transmits the stored configuration messages.
This field displays the path cost to the LAN segment to which the port is connected when the
port is a designated port. Otherwise, it displays the path cost to the root bridge from the
designated port for the LAN segment to which this port is connected.
This field displays the state of the port on which root guard is enabled.
•
Root – inconsistent – the Switch receives superior BPDUs on the port and blocks the port.
•
Forwarding – the Switch unblocks and allows the port to forward frames again.
GS2220 Series User's Guide
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