Technical Reference; Mstp Network Example - ZyXEL Communications GS2210 Series User Manual

Table 55 Advanced Application > Spanning Tree Protocol > Status: MSTP (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.
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/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 segament 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 unbolcks and allows the port to forward frames again.
GS2210 Series User's Guide
139