Brought to you by EarthWeb
IT Library Logo

Click Here!
Click Here!


Search the site:
 
EXPERT SEARCH -----
Programming Languages
Databases
Security
Web Services
Network Services
Middleware
Components
Operating Systems
User Interfaces
Groupware & Collaboration
Content Management
Productivity Applications
Hardware
Fun & Games

EarthWeb Direct EarthWeb Direct Fatbrain Auctions Support Source Answers

EarthWeb sites
Crossnodes
Datamation
Developer.com
DICE
EarthWeb.com
EarthWeb Direct
ERP Hub
Gamelan
GoCertify.com
HTMLGoodies
Intranet Journal
IT Knowledge
IT Library
JavaGoodies
JARS
JavaScripts.com
open source IT
RoadCoders
Y2K Info

Previous Table of Contents Next


Redundancy

Redundant switch configurations can be created with the Spanning Tree Protocol (STP). Using STP switches can be connected in redundant mesh topologies that will recover in the event of a link or switch failure. As with the Management/Control concerns, deploying too many switches in a spanning tree can limit the effectiveness of the redundancy. If large numbers of switches are participating in a tree, then recovery from topology changes can take significantly longer than smaller broadcast domains.

Key Design Points

When designing the switched portion of a LAN infrastructure, determining the appropriate size for each broadcast domain is fundamental. Once this decision is made, the appropriate amounts of performance (segmentation) and redundancy can be applied.

Network designers should be mindful of protocol issues when allocating broadcast domains. For example, each IP subnet should contain no more than one (switch defined) broadcast domain, because the protocol itself defines a broadcast domain within each subnet. The same is generally true for IPX networks (although a little more flexibility is possible) — each IPX network should contain no more than one broadcast domain.

When to Use Routing

Routing is the perfect complement to a switched LAN infrastructure. Routers are typically the best way to connect broadcast domains — particularly when routable protocols such as IP, IPX, and DecNet are used within the network. When connections to WAN interfaces are required, routers provide the deepest feature set for converting LAN-oriented traffic to wide area formats. Finally, secure environments will require a router to provide a measure of isolation from non-authorized user communities.

Through the use of dynamic routing protocols such as RIP and OSPF, large scale fault tolerant networks can be created utilizing hundreds of routers. (See Exhibit 3-7-9.)


Exhibit 3-7-9.  Routing Adds Control

Risk Factors — Routing

Although implementing routing does provide an increased measure of management and security to switched and shared networks, other factors must be weighed before determining the extent to which routing should be deployed.

Performance

Today's highest performance routers are capable of forwarding approximately one million packets per second — a performance level more than adequate for last year's traffic. However, recent events such as the rapid adoption of Fast Ethernet (100M bps) and Gigabit Ethernet (1000M bps), combined with a traffic model oriented towards intranet architectures (where IP traffic commonly traverses subnet boundaries) are overloading traditional routers.

Because routing is an important function to network operation, a new generation of Layer 3 switches (also known as Wire Speed IP Routers), are now being offered to alleviate the IP router bottleneck. These new products can process between five and twelve million IP packets per second. These performance levels allow network designers more creativity (flexibility) when determining where routing should be utilized in a network.

Key Design Points

Forgetting briefly the performance limitations of traditional routers, and thinking purely about routing functions, designers need to determine the optimal locations for routers in their networks. The same review which determined the best size for broadcast domains (in the switching section) must occur for routers as well (see Exhibit 3-7-10). Designers must review each protocol (IP, IPX, DecNet, etc.) and determine where traditional multiprotocol routers should reside, and where high speed Layer 3 switches should complement them.


Exhibit 3-7-10.  Layer 3 Switch Example

Currently, most high speed Layer 3 implementations perform limited firewall, multiprotocol (non IP) and WAN functions. Using Layer 3 switches (wire-speed IP routers) for local IP traffic forwarding can free CPU and memory resources on traditional routers for these other tasks.

When to Implement VLANs

VLANs are probably the most misunderstood component of modern networking. Switch vendors have expended so much energy touting how many VLANs their switches support and all the mechanisms available for creating VLANs, that many network architects feel that they must somehow implement VLANs in their designs. In fact, VLANs are not universally helpful for all networks. They can be instrumental in some situations, and this section will focus on those instances where VLANs make sense.


Previous Table of Contents Next

footer nav
Use of this site is subject certain Terms & Conditions.
Copyright (c) 1996-1999 EarthWeb, Inc.. All rights reserved. Reproduction in whole or in part in any form or medium without express written permission of EarthWeb is prohibited. Please read our privacy policy for details.