MNS-BB
Software User Guide
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participate in frame transfer. In a network of RSTP bridges the time spent in this state is usually quite
short. RSTP bridges operating in STP compatibility mode will spend 6 to 40 seconds in this state.
After ‘learning’ the bridge will place the port in the forwarding state. The port both learns addresses
and participates in frame transfer while in this state.
14.4
Spanning Tree Options: RSTP (802.1w) and STP (802.1D)
14.4.1 RSTP (802.1w)
The IEEE 802.1D version of spanning tree (STP) can take a fairly long time to resolve all the possible
paths and to select the most efficient path through the network. The IEEE 802.1w Rapid
Reconfiguration Spanning Tree (RSTP) significantly reduces the amount of time it takes to establish
the network path. The result is reduced network downtime and improved network robustness.
In addition to faster network reconfiguration, RSTP also implements greater ranges for port path costs
to accommodate the higher and higher connection speeds that are being implemented.
RSTP is designed to be compatible with IEEE 802.1D STP, and Blackbox recommends that you
employ it in your network.
14.4.2 STP (802.1D)
The IEEE 802.1D version of spanning tree has been in wide use and can coexist in a network in
which RSTP (802.1w) has been introduced. If your network currently uses 802.1D STP and you are
not yet ready to implement RSTP, you can apply STP to the switch until such time as you are ready to
move ahead with RSTP. STP offers the full range of STP features found in earlier product releases.
14.5
Transitioning from STP to RSTP
IEEE 802.1w RSTP is designed to be compatible with IEEE 802.1D STP. Even if all the other
devices in your network are using STP, you can enable RSTP on your switch, and even using the
default configuration values, your switch will interoperate effectively with the STP devices. If any of
the switch ports are connected to switches or bridges on your network that do not support RSTP,
RSTP can still be used on this switch. RSTP automatically detects when the switch ports are
connected to non-RSTP devices in the spanning tree and communicates with those devices using
802.1D STP BPDU packets.
Because RSTP is so much more efficient at establishing the network path, it is highly recommended
that all your network devices be updated to support RSTP. RSTP offers convergence times of less
than one second under optimal circumstances. To make the best use of RSTP and achieve the fastest
possible convergence times, though, there are some changes that you should make to the RSTP
default configuration.
Note
Under some circumstances, it is possible for the rapid state transitions employed by RSTP to
result in an increase in the rates of frame duplication and disordering in the switched LAN. In order to
allow RSTP switches to support applications and protocols that may be sensitive to frame duplication
and disordering, setting the Force Protocol Version parameter to
STP-compatible
allows RSTP to be
operated with the rapid transitions disabled. The value of this parameter applies to all ports on the
switch.
As indicated above, one of the benefits of RSTP is the implementation of a larger range of port path
costs, which accommodates higher network speeds. New default values have also been implemented
for the path costs associated with the different network speeds. This can create some incompatibility
between devices running the older 802.1D STP and your switch running RSTP.
14.6
Configuring Rapid Reconfiguration Spanning Tree (RSTP)
This section describes the operation of the IEEE 802.1w Rapid Spanning Tree Protocol (RSTP).
Note
: The default switch configuration has active spanning tree (STP) and disabled.
14.6.1 Optimizing the RSTP Configuration
To optimize the RSTP configuration on your switch, follow these steps
1. Set the switch to support RSTP (STP is the default):
Syntax:
set stp type=rstp
2. Save and Reboot the switch.
3. Enable RSTP Spanning Tree
