© 1999, Cisco Systems, Inc. 1-1

Chapter 2

Overview of a Campus Network

Overview of a Campus Network

© 1999, Cisco Systems, Inc.

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-2

• Discuss the forces that impact the design of campus networks

• Describe Layer 2, 3, 4, and Multilayer Switching functions

• Identify the hierarchical layer solution for a given network requirement

• Discuss the elements of the building block approach

• Identify the correct Cisco product solution, given a set of customer requirements

ObjectivesObjectives

Upon completion of this chapter, you will be able to perform the following tasks:

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-3

In this chapter, we discuss the following topics:

• Campus network overview

• The emerging campus model

• The hierarchical model

Campus Network Overview

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-4

The following section discusses:

Campus Network Overview

• Traditional Campus Networks

• Issues and Solutions

• Traffic Patterns

The Emerging Campus Model

The Hierarchical Model

Campus Network Overview (cont.)

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-5

Characteristics of a Campus Network

TokenRing

TokenRing

• Fixed geographic area

• Owned and administered by organization

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-6

Traditional Campus NetworksTraditional Campus Networks

Collision Domain 1 Collision Domain 2

Broadcast Domain

• Bridges terminate collision domains

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-7

Performance Issues

• Multicast, broadcast, and unknown destination events become global events

Server A

ARPARPARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

I need to know the MAC

address for Server A

I need to know the MAC

address for Server A

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

ARPARP

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-8

Broadcast Issues

• Broadcasts can consume all available bandwidth• Each device must decode the broadcast frame

Server A

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-9

Solution: Localizing Traffic

10.1.1.0 10.1.2.0

10.1.3.0

• LAN broadcasts terminate at the router interface

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-10

Solution: Localizing Traffic (Cont.)

VLAN3

VLAN2VLAN1

• VLANs contain broadcast traffic and separate traffic flows

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-11

VLAN7

VLAN6VLAN5

Current Campus Networks

VLAN3

VLAN2VLAN1

VLAN10

VLAN9VLAN8

• Layer 3 devices interconnect LAN segments while still containing broadcast domains

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-12

Understanding Traffic Patterns

• Successful network implementations consider traffic patterns

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-13

The 80/20 Rule

• 80 percent of the traffic is local; 20 percent is remote

VLAN3

VLAN2VLAN1

80+%Local Traffic

80+%Local Traffic

80+%Local Traffic

80+%Local Traffic

80+% Local Traffic

80+% Local Traffic

20% Remote Traffic

20% Remote Traffic

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-14

The New 20/80 Rule

• 20 percent of the traffic is local; 80 percent is remote

VLAN3

VLAN2VLAN1

20%Local Traffic

20%Local Traffic

20%Local Traffic

20%Local Traffic

20%Local Traffic

20%Local Traffic

80+% Remote Traffic

80+% Remote Traffic

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-15

VLAN4

Emerging Traffic Patterns

• The 20/80 rule challenges VLAN implementation

VLAN3

VLAN2VLAN1

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-16

• Campus Network Overview

• The Emerging Campus Model

–Customer requirements

–Emerging campus structure

–Switching technologies• The Hierarchical Model

Campus Network Overview

This section discusses the following:

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-17

Customer Network Requirements

• Fast convergence

• Deterministic paths

• Deterministic failover

• Scalable size and throughput

• Centralize applications

• The new 80/20 rule

• Multiprotocol support

• Multicasting

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-18

Emerging Campus Structure

Remote ServicesRemote Services

Enterprise ServicesEnterprise ServicesLocal ServicesLocal Services

• Traffic patterns dictate the placement of services

80% Non- Local Traffic80% Non- Local Traffic

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-19

Local Services

• Devices connected by switches

• Traffic within the same subnet/VLAN

• Traffic does not cross the backbone

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-20

Remote Services

• Devices connected by routers

• Traffic crosses subnet/VLAN

• Segregated by Layer 3

• Traffic may/may not cross the backbone

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-21

Enterprise Services

• Common to all users

• Traffic crosses subnet/VLAN

• Traffic crosses the backbone

• Segregated by Layer 3

• May be grouped by Layer 2

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-22

Basic Layer Terminology

Transport Layer

Data Link

Network Layer

Physical

Session

Presentation

Application

Segments

Packets

Frames

LogicalPorts

Routers

Switches/Bridges

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-23

Layer 2 Switching

Data Link

• Hardware-based bridging

• Wire-speed performance

• High-speed scalability

• Low latency

• MAC address

• Low cost

7

6

5

4

3

2

1

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-24

Impact of Layer 2 Switching

• Layer 2 switched networks have the same characteristics as bridged networks

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-25

Benefits of Routing

• Broadcast control

• Multicast control

• Optimal path determination

• Traffic management

• Logical addressing

• Layer 3 securityE0 10.1.1.1

E1 10.2.2.2

E0 E110.1.1.1 10.2.2.2

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-26

7

6

5

4

3

2

1

Layer 3 Switching

Network Layer

• Hardware-based packet forwarding

• High-performance packet switching

• High-speed scalability

• Low latency

• Lower per-port cost

• Flow accounting

• Security

• QoS

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-28

Layer 4 Switching

Transport Layer

• Based on Layer 3

• Based on application-related information

7

6

5

4

3

2

1

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-29

Multilayer Switching

Transport Layer

7

6

5

4

3

2

1

Data Link

Network Layer

• Combines functionality of:

– Layer 2 switching

– Layer 3 switching

– Layer 4 switching

• High-speed scalability

• Low latency

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-30

• Campus Network Overview

• The Emerging Campus Model

• The Hierarchical Model

–Access, Distribution, and Core Layers

–The building block approach

–Campus network availability example

Campus Network Overview

The following section discusses:

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-31

The Hierarchical Model

Distribution Layer

Core Layer

Access Layer

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-32

Access Layer

• Entry point to the network

• Shared bandwidth

• Layer 2 services

–Filtering

–VLAN membership

Access Layer

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-33

Distribution Layer

• Access aggregation point

• Workgroup services access

• Broadcast domains definition

• InterVLAN routing

• Media translation

• Security

Distribution Layer

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-34

The Core Layer

• Fast transport

• No Layer 3 processing

Core Layer

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-35

Distribution Layer

Core Layer

Access Layer

Choosing a Cisco Product

C4xxx

C5xxxC29xx 35xx

C19xx

Catalyst 19xx/29xx/3500 < 50 portsCatalyst 4xxx < 100 portsCatalyst 5xxx >100 ports

Catalyst 55xxCatalyst 6xxx

Catalyst 55xxCatalyst 85xxCatalyst 65xx

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-37

The Building Block Approach

Building A

SwitchBlock

Building B Building C

CoreBlock

ServerBlock

WAN BlockMainframe Block

TokenRing

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-38

LocalEventLocalEvent

The Switch Block

Switch Block 1 Switch Block 2

Access Layer

Distribution Layer

Access Layer

Distribution Layer

• Broadcast storms are contained to a switch block

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-40

Switch Block Characteristics

• Support one or more subnets/VLANs

• Subnets terminate at the distribution switch

• Access devices have redundant links

• Spanning tree terminates at the switch block boundary

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-41

Sizing the Switch Block

• Type of traffic

• Number of users

• Geographic scope of subnets

• Size of spanning-tree domains

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-42

The Core Block

• A core is required when there are two or more switch blocks

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-43

Core Block Characteristics

• Supports frame, packet, or cell; subnets terminate at the core

• Layer 2 or Layer 3 devices

• Distribution to core links should scale n*100 MBps

• Supports various configurations

• Provides redundant paths for each switch block

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-45

A Collapsed Core

Switch Block 2

Access Layer

Distribution/Core Layer

Switch Block 1

Access Layer

Distribution/Core Layer

Core Connectivity

Core Connectivity

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-46

Switch Block 2

Access Layer

Distribution/Core Layer

Switch Block 1

Access Layer

Distribution/Core Layer

Core Connectivity

Core Connectivity

A Collapsed Core (Cont.)

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-47

The Dual Core

Switch Block 2Switch Block 1

Core Block

Subnet A Subnet B

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-48

The Dual Core (cont.)

Switch Block 2Switch Block 1

Core Block

Subnet A Subnet B

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-49

Sizing the Core

• Routing protocol limitations

• Number of distribution switches

• Number of equal-cost links

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-50

Layer 2 Backbone Scaling

• Spanning tree prohibits core interconnections

• Equal-cost path limits number of independent core switches

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-51

Layer 3 Backbone Scaling

• Fast convergence

• Load balancing

• No peering problems

• Performance/cost issues

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-52

Campus Network Example

M1M2M P1P2

P

X Y

A B C

North Building South Building

D

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-53

Campus Network Example (cont.)

M1M2M P1P2

P

X Y

A B C

North Building South Building

D

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-54

Campus Network Example (cont.)

M1M2M P1P2

P

X Y

A B C

North Building South Building

D

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-55

Campus Network Example (cont.)

M1M2M P1P2

P

X Y

A B C

North Building South Building

D

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-56

Written Exercise

Task 1: Describe Layer 2, 3, 4, and Multilayer Switching functions

Task 2: Identify the switch layer solution for a given network requirement

Task 3: Given a set of user requirements, identify the correct Cisco product solution

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-57

Summary

• Types of traffic affect network performance

• Device location affects traffic patterns

• Additional bandwidth is not the solution

• Multilayer switching combines both Layer 2 and Layer 3 functionality in the same device

• Multilayer design model is scalable

• Each component of the multilayer design has a specific function

• Redundant links provide a fault-tolerant framework

© 1999, Cisco Systems, Inc. www.cisco.com BCMSN—2-58

Review

• Discuss the various trends that have forced a redesign of campus networks.

• Describe the different switching technologies and how they enable Multilayer Switching.

• Explain the multilayer model and how it affects traffic flows in the network.