Alcatel Carrier Internetworking Solutions 6648 User Manual

OmniSwitch Troubleshooting Guide

page 4-1

In order to troubleshoot spanning tree related problems an understanding of the protocol and its features 
are needed. The OmniSwitch supports two Spanning Tree Algorithms; 802.1D (standard) and 802.1w 
(rapid reconfiguration). In addition, the Omniswitch supports two Spanning Tree operating modes: flat 
(single STP instance per switch) and 1x1 (single STP instance per VLAN).

Spanning Tree Protocol is defined in the IEEE 802.1D standard.

The 802.1w amendment to that standard, Rapid Reconfiguration of Spanning Tree, improves upon STP by 
providing rapid reconfiguration capability via Rapid Spanning Tree Protocol

For configuration assistance please read the “Configuring Spanning Tree Parameters” in the appropriate 
OmniSwitch Network Configuration Guide.

The primary purpose for spanning tree is to allow for physical redundancy in a bridged network, while 
assuring the absence of data loops. The protocol allows for dynamic fail-over as well.

One of the most important tools needed in troubleshooting a STP problem, is to be prepared before it 
happens. It is essential to have a network diagram that depicts both the physical (cables) and logical 
(VLANs) configurations. It also very useful to know which ports are normally in blocking/forwarding 
prior to any problem.