Brocade FastIron Ethernet Switch Platform and Layer 2 Swit Uživatelský manuál stáhnout pdf (Strana 318)

Support for Cisco's Per VLAN Spanning Tree plus (PVST+), allows a Brocade device to run multiple

spanning trees (MSTP) while also interoperating with IEEE 802.1Q devices. Brocade ports

automatically detect PVST+ BPDUs and enable support for the BPDUs once detected. The

enhancement allows a port that is in PVST+ compatibility mode due to auto-detection to revert to the

default MSTP mode when one of the following events occurs:

• The link is disconnected or broken

• The link is administratively disabled

• The link is disabled by interaction with the link-keepalive protocol

This enhancement allows a port that was originally interoperating with PVST+ to revert to MSTP when

connected to a Brocade device.

1 Cisco user documentation for PVST/PVST+ refers to the IEEE 802.1Q spanning tree as the Common Spanning Tree (CST).

Overview of PVST and PVST+

Per VLAN Spanning Tree (PVST) is a Cisco proprietary protocol that allows a Cisco device to have

multiple spanning trees. The Cisco device can interoperate with spanning trees on other PVST

devices but cannot interoperate with IEEE 802.1Q devices. An IEEE 802.1Q device has all its ports

running a single spanning tree. PVST+ is an extension of PVST that allows a Cisco device to also

interoperate with devices that are running a single spanning tree (IEEE 802.1Q).

Enhanced PVST+ support allows a Brocade device to interoperate with PVST spanning trees and the

IEEE 802.1Q spanning tree at the same time.

IEEE 802.1Q and PVST regions cannot interoperate directly but can interoperate indirectly through

PVST+ regions. PVST BPDUs are tunnelled through 802.1Q regions, while PVST BPDUs for VLAN 1

(the IEEE 802.1Q VLAN) are processed by PVST+ regions. The following figure shows the interaction

of IEEE 802.1Q, PVST, and PVST+ regions.

FIGURE 67 Interaction of IEEE 802.1Q, PVST, and PVST+ regions

Overview of PVST and PVST+

318 FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide

53-1003086-04

1 2 ... 313 314 315 316 317 318 319 320 321 322 323 ... 453 454

Žádné komentáře

Brocade FastIron Ethernet Switch Platform and Layer 2 Swit Uživatelský manuál Strana 318