1 © 2003, cisco systems, inc. all rights reserved. ccnp 1 v3.0 module 1 overview of scalable...

1© 2003, Cisco Systems, Inc. All rights reserved.

CCNP 1 v3.0 Module 1 Overview of Scalable

Internetworks


Objectives

• The Hierarchical Network Design Model

• Key Characteristics of Scalable Internetworks

• Case Study


Objectives


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.


Scalable Network Design

Network is broken into smaller, more manageable segments


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.


The Three-layer Hierarchical Design Model

Cisco offers a three-tiered hierarchy as the preferred approach to network design.


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.


Core Layer Example


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.


Distribution Layer Example


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)


Access Layer Example


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.


Characteristics of Scalable Internetworks

• Reliable and available

• Responsive

• Efficient

• Adaptable

• Accessible but secure


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


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.


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


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


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.


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.


Types of Queuing

• First-in, first-out (FIFO) queuing

• Priority queuing

• Custom queuing

• Weighted fair queuing (WFQ)

• Class-based weighted fair queuing (CBWFQ)


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…


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.


Case StudyInternational Travel Agency, Inc.


Summary

1 © 2003, cisco systems, inc. all rights reserved. ccnp 1 v3.0 module 1 overview of scalable...

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