Chapter 7
| Spanning Tree Algorithm
Configuring Global Settings for STA
– 184 –
implemented on a network, the path between specific VLAN members may be
inadvertently disabled to prevent network loops, thus isolating group
members. When operating multiple VLANs, we recommend selecting the MSTP
option.
◆ Rapid Spanning Tree Protocol
2
RSTP supports connections to either STP or RSTP nodes by monitoring the
incoming protocol messages and dynamically adjusting the type of protocol
messages the RSTP node transmits, as described below:
■
STP Mode – If the switch receives an 802.1D BPDU (i.e., STP BPDU) after a
port’s migration delay timer expires, the switch assumes it is connected to
an 802.1D bridge and starts using only 802.1D BPDUs.
■
RSTP Mode – If RSTP is using 802.1D BPDUs on a port and receives an RSTP
BPDU after the migration delay expires, RSTP restarts the migration delay
timer and begins using RSTP BPDUs on that port.
◆ Multiple Spanning Tree Protocol
MSTP generates a unique spanning tree for each instance. This provides
multiple pathways across the network, thereby balancing the traffic load,
preventing wide-scale disruption when a bridge node in a single instance fails,
and allowing for faster convergence of a new topology for the failed instance.
■
To allow multiple spanning trees to operate over the network, you must
configure a related set of bridges with the same MSTP configuration,
allowing them to participate in a specific set of spanning tree instances.
■
A spanning tree instance can exist only on bridges that have compatible
VLAN instance assignments.
■
Be careful when switching between spanning tree modes. Changing
modes stops all spanning-tree instances for the previous mode and restarts
the system in the new mode, temporarily disrupting user traffic.
Parameters
These parameters are displayed:
Basic Configuration of Global Settings
◆ Spanning Tree Status – Enables/disables STA on this switch. (Default: Enabled)
◆ Spanning Tree Type – Specifies the type of spanning tree used on this switch:
■
STP: Spanning Tree Protocol (IEEE 802.1D); i.e., when this option is selected,
the switch will use RSTP set to STP forced compatibility mode).
■
RSTP: Rapid Spanning Tree (IEEE 802.1w); RSTP is the default.
■
MSTP: Multiple Spanning Tree (IEEE 802.1s)
2. STP and RSTP BPDUs are transmitted as untagged frames, and will cross any VLAN
boundaries.
To Next Page
Loading...
