HP ProCurve 4104GL, Management And Configuration Manual

Page: 316 / 504

13-8
802.1w Rapid Spanning Tree Protocol (RSTP) and 802.1d Spanning Tree Protocol (STP)
Configuring Rapid Reconfiguration Spanning Tree (RSTP)
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,
though, that 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. See “Opti-
mizing the RSTP Configuration” below, for more information on these
changes.
N o t e
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 misordering in the switched LAN. In order to allow RSTP switches to
support applications and protocols that may be sensitive to frame duplication
and misordering, setting the Force Protocol Version parameter to
STP-com-
patible allows RSTP to be operated with the rapid transitions disabled. The
value of this parameter applies to all ports on the switch. See information on
Force Version on page 13-12.
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.
Please see the “Note on Path Cost” on page 13-15 for more information on
adjusting to this incompatibility.