T
raditional network management methods have typi-
cally emphasized bandwidth and reliability. As net-
work complexity increases, however, administrators
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
implementation.
Load balancing with Multiple Spanning Tree Protocol
Understanding MSTP first requires understanding the basic
Spanning Tree Protocol (STP) for link management, defined
in the IEEE 802.1d standard. A Layer 2 switch builds a for-
warding table by learning the Media Access Control (MAC)
addresses of the frames entering the switch. If it does not
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.
STP is designed to provide path redundancy while pre-
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
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
Related Categories:
Dell PowerConnect switches
Dell PowerEdge
blade servers
Ethernet
Network fabric
Visit
www.dell.com/powersolutions
for the complete category index.
Advanced Configuration
for the
Dell PowerConnect
5316M Blade Server
Chassis Switch
Enterprises can take advantage of advanced configuration options
for the Dell
™
PowerConnect
™
5316M Gigabit Ethernet switch for the
Dell PowerEdge
™
blade server chassis to help optimize network
access for blade servers.
By Surendra Bhat
SauraBh Mallik
network and communications
DELL
POWER
SOLUTIONS |
May 2007
1
reprinted from
Dell Power Solutions,
May 2007. Copyright © 2007 dell inc. all rights reserved.
