Home > Articles > Cisco Network Technology > General Networking > Network Security Basics

Network Security Basics

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: May 7, 2004.

Chapter Description

Robyn Aber help us to explore how 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.

LAN Switching

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 scalability—The network can expand easily as the business grows.

  • Improved bandwidth performance for each network user—This is important in environments where users operate multimedia applications or conduct frequent client/server database interactions.

  • Multiple simultaneous connections—Many 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 delay—This 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 failure—With 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 switches—Also called desktop or workgroup switches.

  • Layer 3 switches—Also 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 1Figure 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:

  • Value—The cost of switches is essentially the same as hubs. Users get significantly more price/performance value from switches than they do from hubs.

  • Scalability—The limited, shared bandwidth of a hub network restricts its growth. As users and applications are added, network performance and availability often drop dramatically.

  • Latency—Latency (or delay) can become unacceptable as the network expands, again compromising performance.

  • Failure—Hub-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 visibility—Switches have no indication of the location of particular devices in a distributed network. They know only about devices that are directly connected.

  • Scalability—Switches 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.

VLANs

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 used—even 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

Figure 2

VLAN Benefits

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:

  • Security—Groups that have sensitive data are separated from the rest of the network, decreasing the chances of confidential information breaches.

  • Cost reduction—Cost 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 performance—Dividing flat Layer 2 networks into multiple logical workgroups (broadcast domains) reduces overall network utilization and boosts performance.

  • Broadcast storm mitigation—Dividing a network into smaller logical networks results in lower susceptibility to broadcast storms.

  • Simpler project or application management—VLANs bring together all required players in a way that makes managing a project or working with a specialized application easier.

  • Improved IT staff efficiency—Moves, 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 3Figure 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 performance—They deliver wire speed to the desktop, which helps mitigate network bottlenecks.

  • Ease of use—They are easy to install and configure, and they offer unified management.

  • Scalability—They can grow from small to very large networks.

  • Compatibility—They 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.

3. Intelligent LAN Switch Adoption Considerations | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020