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1© 2003, Cisco Systems, Inc. All rights reserved.
CCNP 1 v3.0 Module 1 Overview of Scalable
Internetworks
222© 2003, Cisco Systems, Inc. All rights reserved.
Objectives
• The Hierarchical Network Design Model
• Key Characteristics of Scalable Internetworks
• Case Study
444© 2003, Cisco Systems, Inc. All rights reserved.
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.
555© 2003, Cisco Systems, Inc. All rights reserved.
Scalable Network Design
Network is broken into smaller, more manageable segments
666© 2003, Cisco Systems, Inc. All rights reserved.
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.
777© 2003, Cisco Systems, Inc. All rights reserved.
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.
101010© 2003, Cisco Systems, Inc. All rights reserved.
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
• 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)
141414© 2003, Cisco Systems, Inc. All rights reserved.
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.
181818© 2003, Cisco Systems, Inc. All rights reserved.
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
202020© 2003, Cisco Systems, Inc. All rights reserved.
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.
212121© 2003, Cisco Systems, Inc. All rights reserved.
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.
222222© 2003, Cisco Systems, Inc. All rights reserved.
Types of Queuing
• First-in, first-out (FIFO) queuing
• Priority queuing
• Custom queuing
• Weighted fair queuing (WFQ)
• Class-based weighted fair queuing (CBWFQ)
232323© 2003, Cisco Systems, Inc. All rights reserved.
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…
242424© 2003, Cisco Systems, Inc. All rights reserved.
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 1This example puts http traffic in the high priority que and everything elseIn the medium priority que.
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