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

333 © 2003, Cisco Systems, Inc. All rights reserved. Objectives

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.

888 © 2003, Cisco Systems, Inc. All rights reserved. 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.

999 © 2003, Cisco Systems, Inc. All rights reserved. Core Layer Example

10 © 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.

11 © 2003, Cisco Systems, Inc. All rights reserved. Distribution Layer Example

12 © 2003, Cisco Systems, Inc. All rights reserved. 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)

13 © 2003, Cisco Systems, Inc. All rights reserved. Access Layer Example

14 © 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.

15 © 2003, Cisco Systems, Inc. All rights reserved. Characteristics of Scalable Internetworks Reliable and available Responsive Efficient Adaptable Accessible but secure

16 © 2003, Cisco Systems, Inc. All rights reserved. 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

17 © 2003, Cisco Systems, Inc. All rights reserved. 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.

18 © 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

19 © 2003, Cisco Systems, Inc. All rights reserved. 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

20 © 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.

21 © 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.

22 © 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)

23 © 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…

24 © 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 1 This example puts http traffic in the high priority que and everything else In the medium priority que.

25 © 2003, Cisco Systems, Inc. All rights reserved. Case Study International Travel Agency, Inc.

26 © 2003, Cisco Systems, Inc. All rights reserved. Summary