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CCNP 1 v3.0 Module 1
Overview of Scalable
Internetworks
© 2003, Cisco Systems, Inc. All rights reserved.
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Objectives
• The Hierarchical Network Design Model
• Key Characteristics of Scalable
Internetworks
• Case Study
© 2003, Cisco Systems, Inc. All rights reserved.
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Objectives
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Building Scalable Networks
• Scalability is the capability of a network to
grow and adapt without major redesign or
reinstallation.
–Redesign may be significant and costly.
• Good design is the key to the capability of
a network to scale.
• A network design should follow a
hierarchical model to be scalable.
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Scalable Network Design
Network is broken into smaller, more manageable segments
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Hierarchical Design Model
• A hierarchical network design model breaks
the complex problem of network design into
smaller, more manageable levels.
• Each level, or tier in the hierarchy addresses
a different set of problems.
• This helps the designer optimize network
hardware and software to perform specific
roles.
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The Three-layer Hierarchical Design Model
Cisco offers a three-tiered hierarchy as the
preferred approach to network design.
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Router Function in the Hierarchy
• The core, distribution, and access layers each
have clearly defined functions.
• Each layer demands a different set of features
from routers, switches, and links.
• The router is the primary device that maintains
logical and physical hierarchy in a network,
therefore, proper and consistent configurations
are imperative.
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Core Layer Example
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The Core Layer
• The core layer provides an optimized and reliable
transport structure by forwarding traffic at very
high speeds.
• To do this, the core layer should not perform any
of the following processes:
–Access-list checking
–Data encryption
–Address translation
• The core must be designed to be the most
reliable and available layer.
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Distribution Layer Example
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Distribution Layer Example
•
The purpose of the distribution layer is to
provide boundary definition using access lists
and other filters to limit what gets into the core.
•
Distribution layer routers bring policy to the
network by using a combination of the
following:
–
Access lists
–
Route summarization
–
Distribution lists
–
Route maps
–
Other rules to define how a router should deal with
traffic and routing updates (policy based routing)
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Access Layer Example
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The Access Layer
• The access layer supplies traffic to the network
and performs network entry control
• End users access network resources by way of
the access layer
• The access layer employs access lists designed
to prevent unauthorized users from gaining entry
or from segment to another.
• The access layer is also how the remote site
connects the WAN.
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Characteristics of Scalable Internetworks
• Reliable and available
• Responsive
• Efficient
• Adaptable
• Accessible but secure
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Making the Network Reliable and Available
• Provides users with 24 hour a day, seven day a
week access
• Fault tolerance and redundancy make outages
and failures invisible to the end user
–Redundant links and devices
• Core routers reroute traffic in the event of a failure
• IOS features that enhance reliability & availability:
–Support for scalable routing protocols
–Alternate paths
–Load balancing
–Protocol tunnels
–Dial backup
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Making the Network Responsive
• End users notice network responsiveness as they use the
network to perform routine tasks.
• Networks must be configured to meet the needs of all
applications, especially time delay sensitive applications such
as voice and video.
• Routers may be configured to prioritize certain kinds of traffic
based on protocol information, such as TCP port numbers.
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Making the Network Efficient
• To be efficient, routers should prevent
unnecessary traffic from traversing the WAN and
minimize the size and frequency of routing
updates.
• The IOS includes several features designed to
optimize a WAN connection:
–Access lists
–Snapshot routing
–Compression over WANs
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Making the Network Adaptable
• An adaptable network will handle the addition
and coexistence of multiple routed and routing
protocols and applications.
• EIGRP is an exceptionally adaptable protocol
because it supports routing information for three
routed protocols:
–IP
–IPX
–AppleTalk
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Making the Network Accessible But Secure
• Accessible networks let
users connect easily over
a variety of technologies.
–SSH, VPN, RAS, RDP
• Often, the easier it is for legitimate remote users
to access the network, the easier it is for
unauthorized users to break in.
• An access strategy must be carefully planned
so that resources, such as remote access
routers and servers, are secure.
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Priority and Queuing
• Traffic prioritization ensures that packets
carrying mission-critical data take precedence
over less important traffic.
• If the router schedules these packets for
transmission on a first-come, first-served basis,
users could experience an unacceptable lack of
responsiveness.
• The IOS addresses priority and responsiveness
issues through queuing.
• By using queuing, higher priority packets are
sent first.
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Types of Queuing
• First-in, first-out (FIFO) queuing
• Priority queuing
• Custom queuing
• Weighted fair queuing (WFQ)
• Class-based weighted fair queuing
(CBWFQ)
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Priority Queuing
• Priority queuing allows traffic types to be
associated with one of four priorities: high,
medium, normal, and low.
• Priority queuing will transmit all packets in the
high queue first.
• When the high queue is empty, then packets
in the medium queue will be transmitted and
so on…
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Priority Queuing Example
From Global Configuration Mode:
access-list 101 permit tcp any any eq 80
priority-list 1 protocol ip high list 101
access-list 102 permit ip any any
priority-list 1 protocol ip medium list 102
interface serial 0/0
-if)# priority-group 1
This example puts http traffic in the high priority que and everything else
In the medium priority que.
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Case Study
International Travel Agency, Inc.
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Summary
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