Design Guide
A scenario wherein BPDUs are lost may be caused by unidirectional links, which can cause Layer 2 loops. To prevent this problem, use Loop Guard and UDLD. Loop Guard prevents a port from forwarding as a result of missed BPDUs, which might cause a Layer 2 loop that could bring down the network.
UDLD allows devices to monitor the physical configuration of fiberoptic or copper Ethernet cables and detect when a unidirectional link exists. When a unidirectional link is detected, UDLD shuts down the affected port and generates an alert. BPDU Guard prevents a port from being active in a
The Cisco Catalyst Blade Switch 3020 supports Per VLAN Spanning Tree (PVST) and a maximum of 128 spanning- tree instances. RPVST+ is a combination of Cisco PVST Plus (PVST+) and RSTP, provides the flexibility of one
Figure 4 illustrates an example of Spanning Tree Protocol when using two switches in the crossover configuration. Each blade switch is dual homed to each aggregation switch through a 2- port Cisco EtherChannel interface. In this figure the blocked links are indicated in red. In this example, only four of the eight uplinks from each blade switch are used. The network designer can make those EtherChannel uplinks more robust (up to four 4 ports each), or use them to connect other devices such as intrusion detection systems (IDSs) or standalone servers.
Figure 4.
© 2008 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information. | Page 7 of 28 |