Pvst+ Mode; Rapid-Pvst; Mistp Mode - Cisco WS-C6506 Software Manual

Chapter 7 Configuring Spanning Tree
An overview of each mode is provided in this section. Each mode is described in detail in these sections:
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Caution If your network currently uses PVST+ and you plan to use MISTP on any switch, you must first enable
MISTP-PVST+ on the switch and configure an MISTP instance to avoid causing loops in the network.

PVST+ Mode

PVST+ runs on each VLAN on the switch, ensuring that each VLAN has a loop-free path through the
network.
PVST+ provides Layer 2 load balancing for the VLAN on which it runs; you can create different logical
topologies using the VLANs on your network to ensure that all the links are used and no link is
oversubscribed.
Each PVST+ instance on a VLAN has a single root switch. This root switch propagates the spanning-tree
information that is associated with that VLAN to all other switches in the network. This process ensures
that the network topology is maintained because each switch has the same knowledge about the network.

Rapid-PVST+

With software release 8.1(1) and later releases, Rapid-PVST+ is the default spanning-tree protocol that
is used on all Ethernet, Fast Ethernet, and Gigabit Ethernet port-based VLANs on Catalyst 6500 series
switches. Rapid-PVST+ is similar to PVST+. The only difference is that Rapid-PVST+ uses a rapid STP
that is based on IEEE 802.1w instead of 802.1D. Rapid-PVST+ uses the same configuration as PVST+
with minimal additional configuration. See the
page 7-33
immediately on a per-port basis when any topology change is made. UplinkFast and BackboneFast are
enabled, but not active in this mode, as the functionality is built into the rapid STP. Rapid-PVST+
provides for rapid recovery of connectivity following the failure of a bridge, bridge port, or LAN.
A port that is connected to a nonbridging device (for example, a host or a router) is an edge port. A port
that connects to a hub is also an edge port if the hub or any LAN that is connected by it does not have a
bridge. An edge port can start forwarding as soon as the link is up. You must explicitly configure the
ports that are connected to the hosts and routers as edge ports while using Rapid-PVST+.
For complete protocol details

MISTP Mode

MISTP is an optional spanning-tree protocol that runs on Catalyst 6500 series switches. MISTP allows
you to group multiple VLANs under a single instance of spanning tree (an MISTP instance). MISTP
combines the Layer 2 load-balancing benefits of PVST+ with the lower CPU load of IEEE 802.1Q.
An MISTP instance is a virtual logical topology that is defined by a set of bridge and port parameters.
When you map VLANs to an MISTP instance, this virtual logical topology becomes a physical topology.
Each MISTP instance has its own root switch and a different set of forwarding links (different bridge
and port parameters).
OL-8978-04
Configuring PVST+ on the Switch, page 7-26
Configuring MISTP-PVST+ or MISTP on the Switch, page 7-34
for configuration information. In Rapid-PVST+, dynamic CAM entries are flushed
,
"Configuring Rapid-PVST+ on the Switch" section on
see the "Rapid Spanning Tree Protocol" section on page
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Understanding How PVST+ and MISTP Modes Work
7-18.
7-13