Multiple Spanning Tree Protocol (Mstp) - HP procurve 8100fl series Management And Configuration Manual

Spanning-Tree Operation
802.1s Multiple Spanning Tree Protocol (MSTP)
C a u t i o n
9-4
802.1s Multiple Spanning Tree Protocol
(MSTP)
The 802.1D and 802.1w spanning tree protocols operate without regard to a
network's VLAN configuration, and maintain one common spanning tree
throughout a bridged network. Thus, these protocols map one loop-free,
logical topology on a given physical topology. The 802.1s Multiple Spanning
Tree protocol (MSTP) uses VLANs to create multiple spanning trees in a
network, which significantly improves network resource utilization while
maintaining a loop-free environment.
While the per-VLAN spanning tree approach adopted by some vendors
overcomes the network utilization problems inherent in using STP or RSTP,
using a per-VLAN technology with multiple VLANs can overload the switch's
CPU. MSTP on the 8100fl switch complies with the IEEE 802.1s standard, and
extends STP and RSTP functionality to map multiple independent spanning
tree instances onto a physical topology. With MSTP, each spanning tree
instance can include one or more VLANs and applies a separate, per-instance
forwarding topology. Thus, where a port belongs to multiple VLANs, it may be
dynamically blocked in one spanning tree instance, but forwarding in another
instance. This achieves load-balancing across the network while keeping the
switch's CPU load at a moderate level (by aggregating multiple VLANs in a
single spanning tree instance).
MSTP provides fault tolerance through rapid, automatic reconfiguration if
there is a failure in a network's physical topology. With MSTP-capable
switches, you can create a number of MST regions containing multiple
spanning tree instances. This requires the configuration of a number of MSTP-
capable switches. However, it is NOT necessary to do this. You can just enable
MSTP on an MSTP-capable switch and a spanning tree instance is created
automatically. This instance always exists by default when spanning tree is
enabled, and is the spanning tree instance that communicates with STP and
RSTP environments.
Because the switch automatically gives faster links a higher priority, the
default MSTP parameter settings are usually adequate for spanning tree
operation. Also, because incorrect MSTP settings can adversely affect
network performance, you should not change the default values unless you
have a strong understanding of how spanning tree operates.
For MSTP information beyond what is provided in this manual, refer to the
IEEE 802.1s standard.