Dell PowerConnect 5316M Quick Manual

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network and communications

also require advanced management options to help ensure

quality and efficiency. The 16-port Dell PowerConnect 5316M

Gigabit Ethernet switch for the Dell PowerEdge blade server

chassis includes features such as load balancing using

Multiple Spanning Tree Protocol (MSTP), quality-of-service

(QoS) management for traffic priority, and Internet Group

Management Protocol (IGMP) snooping. This article provides

a general overview of these features and examples of their

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implementation.

Dell PowerConnect switches

Load balancing with Multiple Spanning Tree Protocol

Dell PowerEdge

blade servers

Understanding MSTP first requires understanding the basic

Spanning Tree Protocol (STP) for link management, defined

Ethernet

in the IEEE 802.1d standard. A Layer 2 switch builds a for-

Network fabric

warding table by learning the Media Access Control (MAC)

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addresses of the frames entering the switch. If it does not

for the complete category index.

find the destination MAC address for a particular frame in

the MAC address table, it forwards the frame on all ports

other than the source port—meaning that if any loops exist

in the Layer 2 network, frames may be forwarded endlessly

and cause broadcast storms.

venting these types of network loops. It creates a tree topol-

ogy among the various network components by designating

a root bridge for the entire network and another bridge for

each Ethernet segment, which it accomplishes by exchang-

ing Bridge Protocol Data Units (BPDUs) between the switches

DELL POWER SOLUTIONS |

Advanced Configuration

for the Dell PowerConnect

5316M Blade Server

Chassis Switch

Enterprises can take advantage of advanced configuration options

By Surendra Bhat

SauraBh Mallik

for the Dell

Dell PowerEdge

access for blade servers.

raditional network management methods have typi-

cally emphasized bandwidth and reliability. As net-

work complexity increases, however, administrators

STP is designed to provide path redundancy while pre-

May 2007

PowerConnect

5316M Gigabit Ethernet switch for the

™

blade server chassis to help optimize network

™

after considering attributes such as bridge and port priority,

MAC address, and link bandwidth. To help avoid loops,

some ports are placed into the blocking state for all data

while they continue receiving BPDUs. If the network topology

changes, the blocking ports move through the intermediate

listening and learning states before settling in the forward-

ing state.

Although traditional STP does help prevent Layer 2 for-

warding loops in a general network topology, convergence

can take up to 30–60 seconds. Rapid Spanning Tree Protocol

(RSTP), defined in the IEEE 802.1w standard, alters the port

roles and takes advantage of point-to-point wiring to provide

rapid convergence of the spanning tree.

STP and RSTP maintain a single topology instance for all

virtual LANs (VLANs). VLANs create multiple logical networks

that can be grouped by function or application rather than

physical location, and create separate broadcast domains

equivalent to IP subnetworks. Using STP and RSTP with

VLANs can result in suboptimal paths for certain traffic.

However, MSTP, defined in the IEEE 802.1s standard, can

maintain multiple spanning tree instances and assign VLANs

to those instances, allowing the use of different physical

paths for different VLAN traffic and helping create efficient

load balancing for network resources.

When MSTP is enabled on the PowerConnect 5316M

switch, the switch uses RSTP to develop a loop-free topology

for each spanning tree instance. Administrators can enable

MSTP on the switch with the following command:

console(config)# spanning-tree mode mstp