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Implementing Dell PowerConnect 5316M switches

Two examples can help administrators understand how to implement

advanced configuration options for PowerConnect 5316M switches: one

for MSTP and one for QoS.

example mstP implementation

Administrators can use MSTP with PowerConnect 5316M switches to

enable load balancing for a blade server chassis. Figure 5 shows a typical

high-availability implementation using two PowerConnect 5316M chassis

switches along with two external PowerConnect 5324 switches that provide

redundancy and availability in case of a switch failure. MSTP is used to

balance the blade traffic from the PowerConnect 5316M switches to the

two PowerConnect 5324 switches.

For example purposes, assume that the network includes VLANs 2–7,

with VLANs 2–4 assigned to MSTP instance 1 and VLANs 5–7 assigned to

MSTP instance 2. Link aggregation between the PowerConnect 5316M

and PowerConnect 5324 switches groups together multiple links and

helps provide load balancing and fault tolerance. (These configuration

examples still apply when using individual physical interfaces rather

than LAGs.)

To simplify the example, consider the connectivity of only the

PowerConnect 5316M switch shown in the lower right corner of Figure 5.

The cost and priority settings for this switch's LAG 1 and LAG 2 interfaces

can be adjusted separately for MSTP instances 1 and 2 to set the LAG port

roles and states shown in Figure 6. These port roles and states are defined

in the RSTP standard; the root port provides the lowest cost when the

Layer � switch

Dell PowerConnect ��

LAG �

Dell PowerConnect ��M

Figure 5.

Example high-availability MSTP implementation using Dell

PowerConnect 5316M and PowerConnect 5324 switches

mstP instance

Figure 6.

LAG port roles and states for a Dell PowerConnect 5316M switch in the example MSTP implementation

Dell PowerConnect ��

LAG �

Dell PowerConnect ��M

VLans

LaG 1 role

2–4

root

5–7

alternate

switch forwards packets to the root switch and would be in the forwarding

state, while the alternate port offers a different path to the root switch

and would be in the discarding state. Figures 7 and 8 show the resulting

topologies for the two MSTP instances.

If this network had used traditional STP, only one of the LAGs would

carry traffic for all the VLANs. Because MSTP allows multiple forwarding

paths for data traffic, the network can maintain separate logical topolo-

gies for different VLAN groups to help make efficient use of network

resources. A similar setup can also be used with the other PowerConnect

5316M switch.

Layer � switch

Dell PowerConnect ��

LAG �

Discarding

Figure 7.

Network topology for MSTP instance 1 in the example high-

availability MSTP implementation

Layer � switch

Dell PowerConnect ��

LAG �

VLANs �–�

Forwarding

Figure 8.

Network topology for MSTP instance 2 in the example high-

availability MSTP implementation

LaG 1 state

LaG 2 role

Forwarding

alternate

discarding

root

www.dell.com/powersolutions

Dell PowerConnect ��

LAG �

VLANs �–�

Forwarding

Dell PowerConnect ��M

Dell PowerConnect ��

LAG �

Discarding

Dell PowerConnect ��M

LaG 2 state

discarding

Forwarding