D-Link DGS-6600 Series Specifications download pdf (Page 14)

Switches for

aggregation

The aggregation network is where

the uplinks from the access network

switches are terminated. That

implies the use of Layer 3 Switches

for aggregation, able to route trac

between access networks and up to

the core network, where necessary.

Port density isn’t a major issue here,

but support for high-bandwidth

Unshielded Twisted Pair (UTP) and/or

bre optic connections is, added to

which aggregation switches require

sucient switching capability to ensure

they don’t become a bottleneck.

Moreover, because they service

multiple access networks, availability

is a major consideration, with

redundant power supplies being

common together with support for

link aggregation and failover.

Note that on smaller networks the

aggregation and core networks

may be combined. Either way, the

switches involved will normally be

fully Managed, in either stackable or

chassis-based formats to provide the

scalability required and the ability to

support other technologies.

Key selling points:

Scalable capacity to avoid bottlenecks;

high availability features (redundant

power, link aggregation and failover);

Layer 3 routing capabilities

Look for:

Managed Switches with Layer 3

routing; multiple high-bandwidth

downlinks; bre optic and 10GbE

capabilities; high capacity fabric;

redundancy and failover; chassis-based

or stackable; technology to avoid

looping over multiple inter-switch links

(e.g. Spanning Tree Protocol)

Where are they used?

In small companies, the aggregation

and core network may be combined

with Access Switches feeding directly

into this combined network. In

larger companies, the aggregation

network will be separate and may be

either distributed – one network per

building, for example – or centralised

with, for example, aggregation and

core switches located in the same

datacentre. Aggregation switches can

also be used to balance loads across

server farms.

Chassis or stack?

Individual switches are limited

when it comes to the number of

ports they provide, so what do

you do when more are needed?

One solution is to daisy chain

switches together but, on a large

network, that’s not a good idea

as each switch still has to be

managed separately plus you’re

using network bandwidth to carry

inter-switch trac. Far better to go

for a custom solution in the form

of either a chassis-based switch or

stackable switch product.

A chassis-based Switch is made

up of a rack-mounted enclosure

(the chassis) and plug-in switch

modules. Each plug-in module is a

self-contained switch, connected

to every other in the chassis by a

high speed backplane separate

from the main network. Modules

can be had in a variety of port

congurations and the chassis

and all its contents managed as

a single entity.

Stackable switches look like and

can be deployed as standalone

switches. In addition, however, they

can be linked together (stacked),

typically, using a dedicated

interface to carry the inter-switch

trac. Just like a chassis, stackable

switches can be managed

together as a single entity.

Don’t need it? Don’t buy it

It’s very easy to get carried away and spend money on features you don’t

necessarily need, especially at the edge of the network where, for example,

Layer 3 routing really isn’t needed. Similarly there’s nothing wrong with

employing commodity products here as these will be just as reliable and

work perfectly well with more complex and expensive aggregation and

core networking hardware.

Switches by location

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D-Link DGS-6600 Series Specifications Page 14

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