A solid network foundation is the key to business agility, process efficiency, productivity, and competitiveness. It provides intelligent services such as security, availability, reliability, and quality of service (QoS). This makes it possible for small-medium companies to run desired business applications and advanced technologies, establish competitive advantage, extend or streamline their operations, improve responsiveness to customers and partners, and reduce the costs of ongoing network management.
Routers and switches are the keys to a strong network foundation. Together they enable the intelligent, end-to-end movement of converged data, voice, and video information within or outside the business.
Switches and routers provide the following network functions:
Switches connect users directly to the network and serve as the primary path for traffic moving within local networks. As more-sophisticated business applications, higher volumes of traffic, and tighter security measures have put greater demands on the network, switches have evolved to give companies greater intelligence and control.
Routers deliver information from a source to its intended destination via the most efficient route across different types of networks. As networks have developed, the line between the roles of switches and routers has continued to blur. The clear trend is toward switches prevailing in the LAN, while routers dominate in the WAN and at the company perimeter (or LAN edge) for WAN access.
Small-medium businesses are becoming increasingly dependent on networks to operate efficiently, serve customers effectively, and work with partners and suppliers more collaboratively. Faced with all the challenges and opportunities of competing in a fast-paced environment, growing companies must be especially confident that their networks can support business evolution. Building an effective network foundation is integral to, and an operational insurance policy for, achieving e-business transformation. You can think of this foundation as equivalent to a person's skeletal structure. It is the support system. The stronger, healthier, and more flexible is, the greater the range of movement, carrying capacity, and longevity or stamina. A network foundation serves that same skeletal role for a business.
It is vital that small-medium businesses focus their attention on the critical success factors that drive growth in their particular market. They cannot afford to expend precious time rearchitecting, relearning, and managing networks. Network infrastructures should be the invisible plumbing that enables the transport of company information and communications and enables efficient processes. When the invisible becomes visible and companies run up against infrastructure limitations, this can lead to revenue losses, information privacy breaches, and customer dissatisfaction. This is because network problems can result in poor responsiveness and/or the dissemination of faulty data. Such occurrences can seriously undermine a company's competitiveness and credibility.
The way to avoid such problems is to ensure that the foundation or core infrastructure is well constructed, adaptable to changing environments, intelligent, and operable with minimal administrative intervention. The network should not be so time-consuming to set up and manage that it detracts from the business's primary focus.
The Value of a Business-Class Network
As noted previously, the key elements of an intelligent network foundation are switches and routers that deliver security, availability, reliability, and quality of service. A business-class network should provide the following capabilities:
Protection from security breachesBudget-conscious small-medium companies might feel particularly conflicted as they weigh the costs associated with implementing comprehensive network security against the cost of potential breaches. When security features are integral to a network's foundation, they simplify management while they protect business operations, improve business resiliency, prevent damage to intellectual property assets, mitigate business disruptions, and reduce the network's total cost of ownership (TCO).
Continuous availability and network reliabilityAs business information systems become ever more strategic to a company's success, so does the importance of keeping them always onlineable to recover from failureand accessible anywhere. The proliferation of powerful desktops and servers running bandwidth-intensive applications has some networks straining to keep up. With each new user, device, or application, the underlying infrastructure comes under that much more stress. The network foundation must be prepared to support increasing numbers of users with 24/7 uptime; run new services and applications; extend its reach to new offices, customers, and partners; and support a more mobile workforce. The bottom-line business impact of an available network is increased productivity.
Quality of serviceQoS lets small-medium businesses use the network infrastructure, including LAN and WAN connections, more efficiently. As networks continue to converge (integrate voice, data, and video into a single network), it becomes increasingly important to ensure the efficient coexistence of high-priority and low-priority information transfer. Incorporating QoS into the network foundation lets you assign higher priority to business-critical applications and delay-sensitive traffic such as voice, video, and real-time transactions.
Network Foundation Relevance
When thinking about the business value of a solid network foundation, you cannot help but ask, "Does this apply to my business?" or "Do I really need this?" A business-class, intelligent network foundation is suitable for use by any small-medium business to which the following criteria apply:
The business depends on a network to handle mission-critical operations.
It runs e-commerce and web applications that exchange real-time information online with customers, partners, and employees.
It is concerned about adding new business applications while maintaining the performance level of existing applications.
It is poised for growth or is experiencing growth that is straining the limits of the existing network infrastructure.
It wants to implement advanced technologies such as IP telephony, storage networks, wireless mobility, and security or a VPN (virtual private network).
It wants to compete or partner with larger businessesin terms of geographic reach, types of customers served, or hours of operation.
The critical network foundation elements (switches and routers), along with their value propositions and related investment decision criteria, are covered in this chapter.
Switches are a fundamental part of most networks. They let multiple users communicate directly with each other. As such, they offer the potential for collision-free, high-speed networking. In essence, switches create a system of simultaneous, parallel, point-to-point connections between pairs of devices.
Here are some benefits that can be realized by using LAN switches:
Increased network scalabilityThe network can expand easily as the business grows.
Improved bandwidth performance for each network userThis is important in environments where users operate multimedia applications or conduct frequent client/server database interactions.
Multiple simultaneous connectionsMany simultaneous data transfers can take place between pairs of devices connected to switch ports. This is not possible with hub-based networks.
Reduced congestion and information transmission delayThis translates to more efficient business application access. Remember that network segmentation is used to minimize the number of users contending for LAN bandwidth on each segment (switch port).
No single point of failureWith proper network design, there are fewer chances for network failure.
Improved manageability and security through the use of virtual LANs (VLANs)VLANs group individual users into logical workgroups with common interests or business functions. Data broadcasts are restricted to designated members of the group (also called the broadcast domain). This functionality gives companies the flexibility to move employees around physically yet still maintain their functional ties via the VLAN without network reconfiguration. VLANs are discussed in more depth later in this chapter.
A small-medium business can choose from a variety of switch types. The most popular options are the following:
Layer 2 switchesAlso called desktop or workgroup switches.
Layer 3 switchesAlso called routing switches or multilayer switches.
Layer 2 Switching
Conventional Ethernet switches are data link layer (Layer 2 or L2) devices. This means that they operate at Layer 2 of the OSI (Open Systems Interconnection) reference model. In general, Layer 2 services enable the transfer of data across physical connections. Figure 4-1 shows how end-user network devices (nodes) connect to L2 switch ports. Like bridges, which also operate at Layer 2, the L2 switch dynamically learns the MAC addresses (Ethernet addresses) of devices on each of its ports. It then switches traffic to the intended ports as needed.
Figure 4-1 Layer 2 Switched LAN Connections
Switches operating at Layer 2 are very fast because they directly switch data from port to port based on the physical hardware addresses (MAC addresses) that are assigned to network devices during manufacturing. The trade-off for their speed is that they usually are not as intelligent as routers. That is, they do not look at the data packets being transferred to learn anything about where they are going or make any filtering or traffic direction decisions about them. Such decisions require end-to-end knowledge of the network. Switches know only about their locally connected devices.
LAN Switches Replace Hubs
Layer 2 desktop switches are designed to replace hubs and to provide each network device with dedicated bandwidth for higher performance. A hub represents the most basic kind of network. It operates at Layer 1, which means that it physically connects nodes (including computers, servers, printers, and so on). When data comes into a hub, the hub broadcasts it to all other network nodes (attached devices). Although hub-based LANs are still implemented in many very small businesses (including home-based businesses), they cannot effectively support the business applications that most companies are deploying today. Besides its lack of advanced functionality, a hub-based network has other shortcomings, including the following:
ValueThe cost of switches is essentially the same as hubs. Users get significantly more price/performance value from switches than they do from hubs.
ScalabilityThe limited, shared bandwidth of a hub network restricts its growth. As users and applications are added, network performance and availability often drop dramatically.
LatencyLatency (or delay) can become unacceptable as the network expands, again compromising performance.
FailureHub-based networks are notorious for failing, because just one faulty device can cause problems for other devices attached to the hub.
An analogy to consider when thinking about the differences between a switched network and a hub network is that of a highway. With a hub, the network is like a single-lane highway, with data traffic often sluggish or backed up because of a problem or even a crash along the road. A switch-based LAN, however, is more like a multilane highway with traffic flowing in both directions. Users communicate at much higher speeds and with far greater reliability on the switch. They can add traffic to the network without slowing one another down and simply bypass any problem.
Most companies find the migration from hubs to intelligent switches to be simple, nondisruptive, and highly cost-effective. Upgrading to a switch from a hub is relatively painless, because the switch accepts the same cabling and connections as the hub it is replacing. For small-medium businesses that are installing a first-time LAN, a switched network approach is clearly the way to go to protect network investments and build in growth headroom.
Layer 2 switched networks, although more robust than hubs and less costly than Layer 3 switches or routers, also have their shortcomings:
End-to-end visibilitySwitches have no indication of the location of particular devices in a distributed network. They know only about devices that are directly connected.
ScalabilitySwitches use flat addressing (that is, they provide a single level of addressing). In an L2 switched network, data messages are sent to all network-attached devices. There is no hierarchy of message delivery, as there is when using routers. This limits transmissions to a single connected workgroup (domain).
Broadcast stormsBroadcast storms saturate a network and create overhead that throttles bandwidth and slows performance. Broadcasts grow with network size and travel throughout switched networks. When growing a Layer 2 switched network from 100 to 1000 users, decision-makers should keep in mind that broadcast volume will grow at least tenfold.
Software-based virtual LANs (VLANs) organize network devices into logical workgroups (or broadcast domains) independent of physical location. VLANs can offer some relief from Layer 2 switching drawbacks and can help manage broadcasts. Many medium-sized companies have adopted VLANs to deal with the limitations of Layer 2 switching. These companies use VLANs to structure a network for growth.
Any device anywhere on an L2 switched network can be a member of a VLAN, regardless of where other VLAN members are located. However, it is essential that these devices be connected to switches that support VLAN functionality. This is usually designated as IEEE 802.1Q-compliant. Each VLAN acts as a separate network. In fact, for members of different VLANs to communicate, a router (or a Layer 3 switch) must be usedeven if they are connected to the same switch. Every VLAN node (and only those nodes) "hears" the broadcast traffic sent by other VLAN members sharing the same VLAN.
Membership in a VLAN is determined by business preferences called policies. Policy criteria can include IP address (listing specific addresses in a domain), port number (assigning physical switch ports to a logical workgroup), or application (such as customer relationship management, sales force automation, call center, and so on). Using business functions as a policy example, the marketing staff might be spread throughout a building, yet if they are all assigned to a single VLAN, they can share resources and bandwidth as if they were connected to the same physical LAN segment or subnet (portion of a network). The resources of other departments, such as finance and engineering, can be invisible to the marketing VLAN members, accessible to all VLANs, or accessible to only certain individuals based on specified IT policy parameters. Figure 4-2 shows VLANs being used to subdivide functional workgroups.
Figure 4-2 Logical VLAN Workgroups
User productivity and adaptability are key drivers for business growth and success. Implementing VLAN technology is becoming a popular means to enable a network to more flexibly support business goals. The primary benefits of using VLANs are as follows:
SecurityGroups that have sensitive data are separated from the rest of the network, decreasing the chances of confidential information breaches.
Cost reductionCost savings result from less need for expensive network upgrades and more efficient use of existing bandwidth and uplinks. Some of the savings are reduced by administrative costs needed for IT staff to configure VLANs into switches.
Higher performanceDividing flat Layer 2 networks into multiple logical workgroups (broadcast domains) reduces overall network utilization and boosts performance.
Broadcast storm mitigationDividing a network into smaller logical networks results in lower susceptibility to broadcast storms.
Simpler project or application managementVLANs bring together all required players in a way that makes managing a project or working with a specialized application easier.
Improved IT staff efficiencyMoves, adds, and changes are easier and less expensive to perform. Network administrators' time is freed up for proactive network management.
Layer 3 Switching
Routing used to be the only way to connect internal business networks. However, the advent of wire speed (10, 100, 1000 Mbps) Layer 3 (L3) switches with virtually no delay now lets LAN traffic be connected without the use of traditional routers in the backbone. Standalone routers mostly have been relegated to handle LAN/WAN edge access and WAN connectivity. This is similar to how high-performance Fast Ethernet and Gigabit Ethernet have nudged ATM from the LAN to the WAN. Figure 4-3 shows how Layer 2/Layer 3 switches dominate in the LAN backbone and in the distribution network and how routers dominate at the network edge for WAN access.
Figure 4-3 Complementary Roles of Switches and Routers
In spite of the benefits they deliver, L3 switches are essentially marketing, rather than technological, innovations. For all practical purposes, an L3 switch is a high-performance router (that is, a hardware-based IP router) that is optimized for use in a company's LAN or intranet. Performance is the key factor that distinguishes an L3 switch from a traditional router. An L3 switch can forward packets many times faster than most routers because it does not have the overhead of supporting multiprotocol functionality or the comprehensive filtering functions of a router. L3 switches are lean, mean machines.
L3 switches do the following:
They route IP packets and sometimes IPX protocol packets. Traditional routers are needed if other protocols need to be routed.
They switch nonroutable traffic at Layer 2 (by MAC address). This helps blur the line between L2 and L3 switches.
They forward frames at wire speed rates with latencies of typically a few microseconds.
They support only LAN-based routing.
Switches are less expensive than traditional routers that have similar performance.
Benefits of L3 switches include the following:
High performanceThey deliver wire speed to the desktop, which helps mitigate network bottlenecks.
Ease of useThey are easy to install and configure, and they offer unified management.
ScalabilityThey can grow from small to very large networks.
CompatibilityThey work seamlessly with L2 switches and traditional routers.
In converged networking environments that carry multimedia traffic, L3 switching is becoming the de facto foundation for meaningful QoS. QoS is needed to support such applications as videoconferencing and IP telephony; it can also provide fast access to centralized servers.
Intelligent LAN Switch Adoption Considerations
When implementing advanced networking technologies (IP telephony, wireless mobility, security, storage networking, and others) and Internet-based business applications, it is vital to deploy intelligent LAN switches as part of a core network foundation. These switches should feature functionality such as the following:
High availability and quick response timeEnsures the reliable delivery of time-critical information.
Integrated securityProtects sensitive areas of the network and its data.
Quality of service (QoS)Network administrators can assign priorities to business-critical traffic for consistent, predictable delivery.
Web-based management and friendly graphical user interfaces (GUIs)Save network administrators time and ensure management efficiency.
Consider a number of criteria and features when choosing an intelligent LAN switch. Select a switch that:
Doesn't drop frames under heavy loads
Delivers low latency (delay measured in microseconds)
Provides local and remote network management options
Offers plug and play installation for quick setup
Offers load balancing for traffic management
Ensures ease of adding bandwidth as the network grows or more-demanding applications are added
Provides redundancy of the switch and its power supplies for backup and network resilience
Offers hot-swappable modules for easy maintenance and uninterrupted network uptime
Offers lower cost per port than traditional routers
Includes or can enable VLAN support to reduce network management costs in growing networks
Factors to Discuss with a Trusted Advisor
Small-medium business decision-makers should ensure that their consultant, reseller, or equipment vendor, as well as their in-house IT staff, take into account the following factors to determine the most appropriate intelligent switches to deploy. There is an array of LAN switch types from which to choose. It is important to select the proper switch to support the business's current and evolving requirements and network budget. Here are some factors to consider in gauging which switch is most suitable:
Current network traffic patternsIdeally, traffic patterns should be baselined for a few weeks to identify which users or groups require higher bandwidth and whether user-generated information flows are one- to-one (peer-to-peer) or many-to-one (client/server). Putting the right number of users on a switch can balance traffic loads and guarantee higher performance.
Company expansion plansSwitches must be able to handle current and future users. Consider the number of employees to be added (or reduced), new buildings on a campus, new functional groups to be formed, company acquisitions that might bring diversified network infrastructures, and so on.
Business software adoption plansBandwidth must be sufficient for the applications to be run. Both current and future media must be considered.
LAN upgrade plansIf the LAN will be upgraded from Ethernet to Fast Ethernet to Gigabit Ethernet, the switch must be able to support that.
Advanced network technology adoption plansBandwidth must be sufficient for any new advanced technologies to be deployed, such as IP telephony to replace PBX systems, storage networking, wireless LANs, network security, and others.
For business-critical and growing networks, a foundation built on intelligent switching offers high performance, availability, scalability, security, and improved manageability for a reasonable cost.
The Role of Routing in Computer Networks
The primary business drivers for routing are to provide ubiquitous, secure, and ready application availability and web access for employees. This must be done with a total cost of ownership (TCO) that is affordable and justifiable in light of the company's objectives and initiatives. When properly used as part of a network foundation, routers can help optimize application availability, improve employee productivity, boost customer responsiveness and loyalty, and spur company competitiveness and time to market. Routers also can help overcome the limitations of geography between small-medium businesses and their customers, partners, and suppliers. They can mitigate business conduct restraints that are tied to physical office locations.
Routers carry out two basic functionsthey select a path between networks, and they securely transmit information packets across that path toward an intended destination. In so doing, they draw on routing protocols and algorithms. These algorithms are designed to plot routes using such criteria as throughput, delay, simplicity, low overhead, reliability/stability, and flexibility. Tables of available routes and their conditions are created so that routers can use the most efficient paths possible for each transmission. This process is similar to maps created by auto clubs that show drivers where roadwork is under way so that they can avoid potential areas of congestion. When a packet is received at a router, the router opens it, looks at the network destination address, and then calculates the next hop in the best, or lowest-cost, route to the destination. A hop is measured by the passage of a packet through a router. For example, if a packet passes through three routers, it uses three hops to reach its destination. Achieving low cost with routing is especially important, because WAN bandwidth is expensive.
Routers can be hardware- or software-based. They are different from Layer 3 switches in that they support multiple protocols besides IP. They can connect different kinds of networks to form internetworks (and therefore are said to be medium-independent). Routers also differ from Layer 2 switches because they enable the building of very large networks, such as the Internet. This is in sharp contrast to the limited scalability of Layer 2 networks using L2 switches. Internetworking is about linking computing devices and workers through a maze of telecommunications lines. This ability to provide communications route diversity across various links is what ensures that business applications sustain an uptime level that is satisfactory to business executives.
To small-medium business end users, routers are merely connectivity devices or intermediaries. The simplest router configuration possible has only two interconnected networks, or interfacesan Ethernet LAN connection and a WAN connection. With the exception of the IT staff that manages them, most network users communicate through routers rather than with routers. In fact, hackers sometimes try to direct traffic to routers to shut down a business. That is the principle behind denial of service (DoS) attacks. Security precautions must be taken to protect against this. Chapter 5, "Network Security Basics," discusses the appropriate precautions.
As mentioned previously, L2/L3 switches now dominate the LAN. Routers work with switches in a complementary manner to provide WAN access. Switches hand off traffic to routers at the network edge to access the Internet or send information across a WAN. The network edge is the demarcation between the company LAN and the WAN, or between a teleworker's home LAN and the WAN. When employees send e-mails or access the web, they are typically sending their messages and information requests locally using switches and across the Internet via a number of routers.
Access Routing Adoption Decision Criteria
Like their switching counterparts, routers that are employed in small-medium businesses should deliver high performance, flexibility, and intelligent business-class services such as the following:
Availability in the form of various types of redundancy and survivability for network resilience.
Security such as VPN support, intrusion detection, integrated firewall, and access control lists (ACLs). Chapter 5 provides more details.
QoS for traffic scheduling, queuing, and policing.
Hot-swappable modules for easy maintenance and uninterrupted network uptime.
Scalable manageability for all sizes of businesses.
Consumer-class routers, although they offer attractive commodity prices, might fail when exposed to the rigors of a growing business's applications. This could bring a business to its knees. Such products also could lead to higher TCO over time and result in a patchwork of networking devices that are difficult to manage. The right router can establish a solid foundation for business networking and growth.
Measuring the Success of a Network Foundation
It is critical that the success of a network foundation deployment be measurable. Here are some metrics that can be established for tracking purposes before an installation:
Increased employee productivity
Improved responsiveness to clients, customers, suppliers, and partners
Reduced network downtime
Improved confidence in adding new software applications
More-dependable and far-reaching application availability
Greater business resilience and agility
Lower administrative and support costs
Small-medium businesses are becoming increasingly dependent on computer networks for efficient operations, responsive customer service, and collaboration with partners. Switches and routers are the keys to a strong network foundation. Together they enable the end-to-end movement of data, voice, and video information.
A network foundation can be considered equivalent to a person's skeletal structure. It is the support system. Like the human skeleton, a network foundation should handle its role invisibly but efficiently. If the network becomes visible, it can become intrusive. If that happens, the network detracts from a company's focus on its core business practices.
Foundational network elements should protect a company from security breaches, ensure continuous operations, and deliver quality of service. The core elements of a network foundation include switches and routers. Switches are a fundamental part of most networks. They let multiple users communicate with each other. Small-medium businesses can choose from a variety of switch types, including Layer 2 and Layer 3. Routers provide scalability, security, ready application availability, and web access for employees. They involve two basic functionsselecting paths between networks and securely transmitting information.
Keep in mind a number of factors when evaluating network switch and router investments. The first criterion is always to ask what a company's business objectives are. The answers will drive the technical criteria for level of availability, type of security, quality of service guarantees, network management, and so on.