Select none if you do not require the switch to manage redundant network connections. All
ports will forward network traffic just as an unmanaged switch would. Otherwise RSTP
(Rapid Spanning Tree Protocol) should usually be selected. A selection of STP or RSTP will
allow redundant links between switches so those links can keep the network connected even
when a primary link fails. RSTP is compatible with switches that only implement STP, an
older version of the protocol. If STP is selected only the original STP format messages will
be generated. Selecting STP reduces the chances of network packets being duplicated or
delivered out of order, but at the expense of much longer reconfiguration time.
Bridge Priority (0 to 61440; Default = 32768): The bridge priority is used to determine
the root bridge in the spanning tree. For MSTP, the bridge priority is used to determine the
CIST root. The priority ranges from 0 to 61440 (default 32768) and must be a multiple of
4096. Lower numbers indicate a better priority.
By default, the bridge with the lowest bridge priority is selected as the root. In the event of a
tie, the bridge with the lowest priority and lower MAC address is selected.
There are two ways to select a root bridge (switch). The first is to leave all the bridge priority
settings at the default setting of 32768. When all the switches are set at the default priority,
the managed switch with the lowest MAC address is selected as the root. This may be
adequate for networks with light or evenly distributed traffic.
The second way to select a root bridge is to customize priority settings of each bridge.
Customizing the bridge priority settings allows the network to select a root bridge that gives
the best network performance. The goal is generally to have the network traffic pass through
the network as directly as possible, so the root should be central in the network. If most
messages are between one central server and several clients, the root should probably be a
switch near the server so messages do not take a long path to the root and another long path
back to the server.
Once you decide which switch should be the root, it should be given the best (numerically
lowest) bridge priority number in the network.
Maximum Age (6 to 40; Default = 20): For STP, the max age indicates the maximum
time (in seconds) that the switch will wait for configuration messages (BPDUs) from other
managed switches. If that time expires, the switch assumes that it is no longer connected to
the root of the network. If a link goes down in a way that the switch can detect the loss of
link, it does not wait before reconfiguring the network.
RSTP waits 3 times the Hello Time instead of Max Age before assuming that it is no longer
connected to the root of the network. However, Max Age is used to limit the number of
hops Spanning Tree information may travel from the root bridge before being discarded as
invalid. Furthermore, MSTP only counts hops that take place to or from switches outside the
CAUTION: If VLANS and redundancy (STP/RSTP/MSTP) are both enabled, situations can arise where
the physical LAN is intact but one or more VLANs are being blocked by the redundancy algorithm and
communication over those VLANS fails. The best practice is to make all switch-to-switch connections
members of all VLANs to ensure connectivity at all times. Should you intend to use RSTP and VLANs
at the same time, please see the “VLAN with RSTP” section for important information concerning the
setup of your network. Otherwise, communication failures may occur.
4-19
Chapter 4 - Managed Switch Software Setup
Stride Industrial Ethernet Switches User Manual 2nd Ed. Rev. A
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