The Design Process
An internetwork requires many layers of thought and design that encompasses
everything from physical space to future network considerations.There are generally
three components when designing a large internetwork: data center networks,
wide area networks (WAN), and remote users (in this case, your external
clients).
Data center networks are generally comprised of locally housed equipment
that will service your clients from a building, or set of buildings.
Wide area networks are the connections between the data center and
the customer.
Remote users are your clients and telecommuter traffic that are subsets
of your main clients.
Designing the network is a challenging task, but as I said earlier, you probably
are doing this job because you like a challenge.You must take into account that
each of the three components has its own distinct requirements. For example, an
internetwork that is comprised of five meshed platforms can create all sorts of
unpredictable problems, so attempting to create an even larger series of intermeshed
networks that connect multiple customers who have their own network
issues can be downright mind-boggling.
This is an age in which equipment is getting faster, sometimes by being more
granular in the services that are offered, and other times, allowing more to be
done within a single chassis. Infrastructure design is becoming more difficult due
to ASPs moving toward more sophisticated environments that use multiple protocols,
multiple media types, and allowing connections to domains outside your
areas of influence because of customer requirements.
One of the greatest trade-offs in linking local area networks (LANs) and
WANs into a packet-switching data network (PSDN) infrastructure is between
cost and performance.The ideal solution would optimize packet-based services,
yet this optimization should not be interpreted to picking the mix of services
that would represent the lowest possible tolls.Your customers are going to want
speed, availability, and ease of use.To successfully implement a packet-service
infrastructure, you should adhere to two basic rules:
When designing and implementing a packet-switching solution, try to
balance cost savings with your company’s internal performance requirements
and promises to its customers.
Try to build a manageable solution that can scale when more links and
services are required by your company’s clientele.
is to create a hierarchical internetwork design that will modularize the elements
of a large internetwork into layers of internetworking.The key layers that
will help you create these modules in this model are the Access, Distribution, and
Core routing layers.
The hierarchical approach attempts to split networks into subnetworks, so
that traffic and nodes can be more readily managed. Hierarchical designs assist in
the scaling of internetworks, because new subnetworks and technologies can be
integrated into the infrastructure without disrupting the existing backbone.This
also makes the swapping out of equipment and upgrades much easier, because it
is a modular environment. Figure 8.2 illustrates the basic approach to hierarchical
Some advantages of a hierarchical approach include:
Inherent scalability
Easier to manage
Allows for the optimization of broadcast and multicast control traffic
Note that this three-tier model is defined by the Core, Distribution, and
Access layers:
The Core layer is where the backbone of the network is located and is
the central point that data must traverse.This area should be designed for
speed.The most important aspect of this layer is to pass information to
the rest of the network.The core should have a meshed, redundant
design for higher efficiency.
The Distribution layer is where your border routers are located. Most
of the routing decisions should be made at this level.This is the area
where you would implement policies for the network.
The Access layer is the customer’s network.This area may allow you
the least control because differing media and protocols may be used.This
is usually the most over-subscribed part of the network.
Scalability of Hierarchical Internetworks
Hierarchical internetworks are more scalable, because they allow you to grow
your internetwork in a gradual way with the implementation of modules.This
allows an infrastructure to grow in increments without running into the limitations
that are normally associated with flat, nonhierarchical infrastructures.The
drawback is that hierarchical internetworks require careful planning and implementation.
There are many issues to consider when designing your network,
including:
The costs that are included in virtual circuits
The complexity that will be inherent in a hierarchical design
(particularly when integrated with a meshed topology)
The need for additional hardware interfaces, which are necessary to
separate the layers within your hierarchy
The scalability of the software and routing protocols
To fully utilize a hierarchical design, you should create your hierarchy with
your regional topologies in mind. Remember that the specifics of the design will
depend on the services you implement, as well as your requirements for fault
tolerance, cost, and overall performance.Always think,“How can I get the most
out of this design, and what are the potential problems that could arise?”
Manageability of Hierarchical Internetworks
There are management advantages inherent to hierarchical designs, such as the
flexibility of your design, the ease of installing these modular segments into your
network, and the management of fewer peers to your main convergence points.
Design flexibility Designs that use the hierarchical approach will provide
greater flexibility in the use of WAN circuit services. Leased lines
can be implemented in the Core, Distribution, and Access layers of the
internetwork.
Internetwork ease By adopting a hierarchical design, you will reduce
the overall complexity of an internetwork by being able to separate the
components into smaller units.This will make troubleshooting easier,
and provide protection against broadcast storms, routing loops, or other
potential problems.
Hardware management The complexity of individual router and
switch configurations is greatly reduced, because each router has fewer
peers with which they need to communicate.
everything from physical space to future network considerations.There are generally
three components when designing a large internetwork: data center networks,
wide area networks (WAN), and remote users (in this case, your external
clients).
Data center networks are generally comprised of locally housed equipment
that will service your clients from a building, or set of buildings.
Wide area networks are the connections between the data center and
the customer.
Remote users are your clients and telecommuter traffic that are subsets
of your main clients.
Designing the network is a challenging task, but as I said earlier, you probably
are doing this job because you like a challenge.You must take into account that
each of the three components has its own distinct requirements. For example, an
internetwork that is comprised of five meshed platforms can create all sorts of
unpredictable problems, so attempting to create an even larger series of intermeshed
networks that connect multiple customers who have their own network
issues can be downright mind-boggling.
This is an age in which equipment is getting faster, sometimes by being more
granular in the services that are offered, and other times, allowing more to be
done within a single chassis. Infrastructure design is becoming more difficult due
to ASPs moving toward more sophisticated environments that use multiple protocols,
multiple media types, and allowing connections to domains outside your
areas of influence because of customer requirements.
One of the greatest trade-offs in linking local area networks (LANs) and
WANs into a packet-switching data network (PSDN) infrastructure is between
cost and performance.The ideal solution would optimize packet-based services,
yet this optimization should not be interpreted to picking the mix of services
that would represent the lowest possible tolls.Your customers are going to want
speed, availability, and ease of use.To successfully implement a packet-service
infrastructure, you should adhere to two basic rules:
When designing and implementing a packet-switching solution, try to
balance cost savings with your company’s internal performance requirements
and promises to its customers.
Try to build a manageable solution that can scale when more links and
services are required by your company’s clientele.
Designing with the Hierarchy in Mind
One of the most beneficial tasks that you can perform in the design of your networkis to create a hierarchical internetwork design that will modularize the elements
of a large internetwork into layers of internetworking.The key layers that
will help you create these modules in this model are the Access, Distribution, and
Core routing layers.
The hierarchical approach attempts to split networks into subnetworks, so
that traffic and nodes can be more readily managed. Hierarchical designs assist in
the scaling of internetworks, because new subnetworks and technologies can be
integrated into the infrastructure without disrupting the existing backbone.This
also makes the swapping out of equipment and upgrades much easier, because it
is a modular environment. Figure 8.2 illustrates the basic approach to hierarchical
Some advantages of a hierarchical approach include:
Inherent scalability
Easier to manage
Allows for the optimization of broadcast and multicast control traffic
Note that this three-tier model is defined by the Core, Distribution, and
Access layers:
The Core layer is where the backbone of the network is located and is
the central point that data must traverse.This area should be designed for
speed.The most important aspect of this layer is to pass information to
the rest of the network.The core should have a meshed, redundant
design for higher efficiency.
The Distribution layer is where your border routers are located. Most
of the routing decisions should be made at this level.This is the area
where you would implement policies for the network.
The Access layer is the customer’s network.This area may allow you
the least control because differing media and protocols may be used.This
is usually the most over-subscribed part of the network.
Scalability of Hierarchical Internetworks
Hierarchical internetworks are more scalable, because they allow you to grow
your internetwork in a gradual way with the implementation of modules.This
allows an infrastructure to grow in increments without running into the limitations
that are normally associated with flat, nonhierarchical infrastructures.The
drawback is that hierarchical internetworks require careful planning and implementation.
There are many issues to consider when designing your network,
including:
The costs that are included in virtual circuits
The complexity that will be inherent in a hierarchical design
(particularly when integrated with a meshed topology)
The need for additional hardware interfaces, which are necessary to
separate the layers within your hierarchy
The scalability of the software and routing protocols
To fully utilize a hierarchical design, you should create your hierarchy with
your regional topologies in mind. Remember that the specifics of the design will
depend on the services you implement, as well as your requirements for fault
tolerance, cost, and overall performance.Always think,“How can I get the most
out of this design, and what are the potential problems that could arise?”
Manageability of Hierarchical Internetworks
There are management advantages inherent to hierarchical designs, such as the
flexibility of your design, the ease of installing these modular segments into your
network, and the management of fewer peers to your main convergence points.
Design flexibility Designs that use the hierarchical approach will provide
greater flexibility in the use of WAN circuit services. Leased lines
can be implemented in the Core, Distribution, and Access layers of the
internetwork.
Internetwork ease By adopting a hierarchical design, you will reduce
the overall complexity of an internetwork by being able to separate the
components into smaller units.This will make troubleshooting easier,
and provide protection against broadcast storms, routing loops, or other
potential problems.
Hardware management The complexity of individual router and
switch configurations is greatly reduced, because each router has fewer
peers with which they need to communicate.
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