Design & Build

How To: Configure Spanning Tree Protocol on BigIron

by brcd-campus.expert on ‎02-02-2012 11:08 PM - edited on ‎04-09-2014 05:07 PM by pmadduru (2,056 Views)

BRCD-ENTERPRISE 2552

 

Contents

 Introduction

 Spanning Tree Protocol (STP) is defined in the IEEE standards in 802.1D. STP has been the primary protocol in Layer 2 LANs since the beginning of the Ethernet. Its purpose is to create a loop-free topology. Spanning tree accomplishes this by defining a single active path between any two network devices. If spanning tree detects multiple paths across the network, it shuts down duplicate paths between the switches, forcing traffic to flow on only one link.

 STP is not as efficient when implemented in large networks. Over the years, enhancements have been defined to remove some of the deficiencies. For example, Rapid Spanning Tree (RSTP) is defined in 802.1w, and Multiple Spanning Tree is defined in 802.1s. However, these versions all rely on the fundamental approach spanning tree uses to avoid routing loops, a root bridge with single links between switches. Convergence time has improved, but limitations still exist when it comes to efficient bandwidth utilization and simple management and configuration.

 

Before You Begin

 

Prerequisites

There is no prerequisite for this technology.

 

Requirements

All switches should be running current operating switching software.

 

 

Components Used

 FCS, FSX, MLX, CES

 

Topic of Discussion

 

By default, STP is disabled on all devices. All ports in the switch belong to VLAN1, the default VLAN. Each VLAN runs its own instance of STP. Additional instances of STP are enabled as each VLAN is configured in the switch. A total of 128 instances of STP, MSTP or RSTP can be configured on a switch. STP can be enabled at a global level, an individual VLAN level, or an individual port level.

 

Figure 1:  Layer 2 Network (Network Building Block - STP)

 

2552_Figure1.png

 

 

Figure 1 shows a layout of a Layer 2 network consisting of four Ethernet switches. All the switches are connected with Ethernet cable and are all operating at Layer 2 running switching software. Five links, a-e, are providing Layer 1 connectivity and all switches have access to every switch at any time. Links d and e are backup links, and only activate if SW1 fails. When SW1 fails, the links for a, b, and c go down. STP is running on all the switches and there is no loop in the network.

 

Design Criteria

 

Standards Used

 

  • 802.1ad — IEEE Standard Provider Bridges
  • 802.1ag — IEEE Standard Connectivity Fault Management
  • 802.1ah — IEEE Standard Provider Backbone Bridges
  • 802.1p — IEEE Draft Standard Wireless Access in Vehicular Environments
  • 802.1Q — IEEE Standard Provider Backbone Bridge Traffic Engineering
  • RFC 4761 — IETF Draft Virtual Private LAN Service (VPLS) Using BGP for Auto-discovery and Signaling
  • RFC 4762 — IETF Draft Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling

Application Sample

Layer 2 application is dominant in the datacenter environment where high availability is needed. Providing high availability at Layer 2 requires having redundant links from the source to destination switches. However, these redundant links stay in standby mode and only operate when the active link goes down. When this happens, the switches go through a link convergence and then enable the shortest link available to backup the failed link. The amount of time for convergence depends on many variables in the network.

 

Layer 2 is also used in the aggregation layer of the network. Using Layer 2 at the aggregation layer creates network reliability that is regarded as resilience. However, in both the application and aggregation layers, a network downtime is expected as the links go through the convergence cycle.

 

Configuration Notes

  • STP is disabled by default
  • Changing the state of the primary port in the trunk group affects all the ports in that trunk group

Configuration Used

Note: The Global STP command can only be enabled if a VLAN has not been configured.

 

The examples below show some of the most common commands used to enable and disable STP.

 

To configure STP on all the ports in all the VLANs in a device:

BigIron RX (config)# spanning-tree

 

To disable STP on all the ports in all the VLANs in a device:

BigIron RX (Config)# no spanning-tree

 

To enable STP on a particular VLAN:

BigIron STP (config)# vlan 10

 

To enable STP on all the ports in a particular VLAN:

BigIron STP (config-vlan-10)# spanning-tree

 

To disable STP on a particular VLAN:

BigIron STP (config)# vlan 10

BigIron STP (config-vlan-10)# no spanning-tree

 

To enable STP per port:

BigIron STP (config)# interface 1/1

BigIron STP (config-if-e-1000-1/1)#spanning-tree

 

To disable STP per port:

BigIron STP (config)#interface 1/1

BigIron STP (config-if-e-1000-1/1)#no spanning-tree

 

Table 1:  STP Bridge Parameters and Default Values

Parameter

Description

Value Range (secs)

Default Setting (secs)

Forward Delay

Listen and Learn Period

4-30

15

Maximum Age

Listen and Topology Change Period

6-40

20

Hello Time

Period of Hello Timer from Root Bridge

1-10

2

 

 

Display Information

To show STP information:

 

BigIron RX# show spanning-tree vlan 10 VLAN 10 - STP instance 1 ------------------------------------------------------- STP Bridge Parameters: Bridge Bridge Bridge Bridge Hold LastTopology Topology Identifier MaxAge Hello FwdDly Time Change Change hex sec sec sec sec sec cnt 8000000480a04000 20 2 15 1 0 0 RootBridge RootPath DesignatedBridge Root Max Hel Fwd Identifier Cost Identifier Port Age lo Dly hex hex sec sec sec 8000000480a04000 0 8000000480a04000 Root 20 2 15 STP Port Parameters: Port Prio Path State Designat- Designated Designated Num rity Cost ed Cost Root Bridge 1/3 128 4 DISABLED 0 0000000000000000 0000000000000000 1/13 128 4 DISABLED 0 0000000000000000 0000000000000000

 

To show detailed STP information:

BigIron RX# show spanning-tree detail vlan 10 VLAN 10 - STP instance 1 ------------------------------------------------------- STP Bridge Parameters: Bridge identifier - 0x8000000480a04000 Root bridge - 0x8000000480a04000 Control ports - ethe 1/3 ethe 1/13 Active global timers - None STP Port Parameters: Port 1/3 - DISABLED Port 1/13 - DISABLED VLAN 20 - STP instance 2 ------------------------------------------------------- STP Bridge Parameters: Bridge identifier - 0x8000000480a04000 Root bridge - 0x8000000480a04000 Control ports - ethe 1/3 ethe 1/13 Active global timers - None STP Port Parameters: Port 1/3 - DISABLED Port 1/13 - DISABLED

 

Related Information

References

Data Center Tech Notes – Spanning Tree Issues in Datacenter Networks

For complete configuration of STP on Brocade Products, please refer to the knowledge documents at www.brocade.com.

 
 
 
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