Download as PDF, TXT or read online from Scribd. Flag for Table of Contents analysis of Cisco LAN Switching technologies, architectures. Index and . addition, as part of the CCIE Professional Development series of Cisco Press, you can. Cisco LAN Switching (CCIE Professional Development series) [Kennedy Clark, Kevin Hamilton] on soundofheaven.info *FREE* shipping on qualifying offers. The most . DownloadCisco lan switching ccie professional development series pdf. Free. Pdf Download Creative web camera drivers model pd write Twitter for.
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CCIE Professional Development: Cisco LAN Switching is essential for . The Catalyst series of switches has set a new standard for performance and features. Cisco LAN Switching (CCIE Professional Development series) · Read more Cisco LAN Switching Configuration Handbook, Second Edition · Read more. The most complete guide to Cisco Catalyst(r) switch network design, operation, and configuration Master key foundation topics such as.
If the bridge does not hear from that source before an aging timerexpires, the bridge removes the entry from the table. Like unicast frames, all stations receive a frame with a broadcast destination address. It depends upon the user's application needs and the workstation capability. This is exactly what switches allow the administrator to build. This might happen if there are too many devices on the network, implying that there is not enough bandwidth available. The information contained in the announcement is only interesting to other Cisco devices and the network administrator.
Writing a book especially one on technology that is as fast-moving as switching is an incredibly demanding process that warrants a huge number of "thank yous.
First, I would like to thank Kevin Hamilton, my co-author. Kevin was willing to jump into a project that had almost been left for dead because I was feeling completely overwhelmed by the staggering amount of work it involved.
I would like to thank Radia Perlman for reading the e-mails and Spanning Tree chapters of an "unknown author. Chris Cleveland and Brett Bartow deserve special mention. There are many people at Cisco to thank… Jon Crawfurd for giving a young NetWare guy a chance with router technology.
Stuart Hamilton for taking this project under his wing. Merwyn Andrade for being the switching genius I someday hope to be. Tom Nosella for sticking with the project through its entirety.
I owe many thanks to the people at Chesapeake Computer Consultants. I would especially like to thank Tim Brown for teaching me one of my first network courses and remaining a faithful friend and mentor. Finally, a very special thanks to my wife for her never-ending love and encouragement. And, to God, for giving me the ability, gifts, and privilege to work in such an exciting and fulfilling career. Kevin Hamilton: A project of this magnitude reflects the hard work of many individuals beyond myself.
Most notably, Kennedy. He repeatedly amazes me with his ability to not only understand minute details for a vast array of subjects many of which are Catalyst related , but to reiterate them without reference to written materials months and even years past the time when he is exposed to the point.
His keen insights to networking and unique methods of communicating them consistently challenge me to greater professional depths. I, therefore, thank Kennedy for the opportunity to join him in this endeavor, and for the knowledge I gained as a result of sharing ink with him. I also must thank the staff and instructors at Chesapeake Computer Consultants for their continuous inspiration and support as we at times felt discouraged thinking we would never write the last page.
And Tim Brown, who taught me that technology can be funny. And lastly, the staff at Cisco Press. Brett Bartow and Chris Cleveland must especially be commended for their direction and vision in this project. They worked hard at keeping us focused and motivated. I truly believe that without their guidance, we could never have produced this book on our own. Icons Used in This Book Throughout the book, you will see the following icons used for the varying types of switches:.
In addition, you will see the usual battery of network device, peripheral, topology, and connection icons associated with Cisco Systems documentation. These icons are as follows:. Printer Phone Workstation Terminal. Foreword With the advent of switching technology and specifically the enormously successful Catalyst Switching products from Cisco Systems, corporatio ns all over the world are upgrading their infrastructures to enable their networks for high bandwidth applications.
Although the original goal of most switched network design was primarily increased bandwidth, the networks of today require much more with the advent of mission critical applications and IP Voice emerging as mainstream networking requirements. It is therefore important not only to reap the bandwidth benefits of Catalyst switching but also learn sound network design principles leveraging all of the features in the Catalyst software suite.
One thing network designers have learned over the years is that things never get any easier when it comes to understanding and evaluating all of the available technologies that appear in standards bodies and are written about in trade magazines.
The key, however, to building and operating a successful network is understanding the basic fundamentals of the relevant technologies, knowing where and how to apply them most effectively in a network, and most importantly leveraging the successes of others to streamline the deployment of the network.
Internetworking design is part art and part science mostly due to the fact that the applications that ride on top of the network have widely varying traffic characteristics. This represents another challenge when designing a network because you might well optimize it to perform for a certain application only to find that a few months later a brand new application places entirely differing demands on the network.
The science part of campus network design relies on a few basic principles. First, every user connects to a port on a switch and so wiring closets are provisioned with Catalyst switches such as the Catalyst family to connect end users either at 10 megabit Ethernet or increasingly megabit Ethernet. The base level of switching capability here is called Layer 2 switching.
There are typically tens to hundreds of wiring closets that need to be connected somehow. Although there are many ways to do this, experience has taught us that a structured approach with some hierarchy is the best technique for a stable and easily expandable network.
Wiring closets then are typically consolidated into a network. If the network is large in size, there can still be a large number of distribution layer switches, and so in keeping with the structured methodology, another layer is used to network the distribution layer together. Often called the core of the network, a number of technologies can be used, typified by ATM, Gigabit Ethernet, and Layer 3 switching.
This probably sounds rather simple at this point, however as you can see from the thickness of this book, there is plenty of art and a lot more science toward making your design into a highly available, easy to manage, expandable, easy to troubleshoot network and preparing you with a solid foundation for new emerging applications.
This book not only covers the science part of networking in great detail in the early chapters, but more importantly deals with real-world experience in the implementation of networks using Catalyst products. The book's authors not only teach this material in training classes but also have to prove that they can make the network work at customer sites.
This invaluable experience is captured throughout the book. Reading these tips carefully can save you countless hours of time experimenting on finding the best way to fine tune your particular network.
In addition, as part of the CCIE Professional Development series of Cisco Press, you can use the experience gained from reading and understanding this book to prepare for one of the most sought after professional certifications in the industry. Introduction Driven by a myriad of factors, LAN switching technology has literally taken the world by storm.
The Internet, Web technology, new applications, and the convergence of voice, video, and data have all placed unprecedented levels of traffic on campus networks. In response, network engineers have had to look past traditional network solutions and rapidly embrace switching.
Cisco, the router company, has jumped heavily into the LAN switching arena and quickly established a leadership position. The Catalyst series of switches has set a new standard for performance and features, not to mention sales. Despite the popularity of campus switching equipment, it has been very difficult to obtain detailed and clear information on how it should be designed, utilized, and deployed. Although many books have been published in the last several years on routing technology, virtually no books have been published on LAN switching.
The few that have been published are vague, out-of-date, and absent of real-world advice. Important topics such as the Spanning-Tree Protocol and Layer 3 switching have either been ignored or received inadequate coverage. Furthermore, most have contained virtually no useful information on the subject of campus design. This book was written to change that.
It has the most in-depth coverage of LAN switching technology in print to date. Not only does it have expansive coverage of foundational issues, but it is also full of practical suggestions. Proven design models, technologies, and strategies are thoroughly discussed and analyzed.
Both authors have drawn on their extensive experience with campus switching technology. As two of the first certified Catalyst instructors, they have first-hand knowledge of how to effectively communicate switching concepts.
Through design and implementation experience, they have a detailed understanding of what works, as well as what doesn't work. Cisco LAN Switching is designed to help people move forward with their knowledge of the exciting field of campus switching. CCIE candidates will receive broad and comprehensive instruction on a wide variety of switching-related technologies. Other network professionals will also benefit from hard-to-find information on subjects such Layer 3 switching and campus design best practices.
Cisco LAN Sw itching should appeal to a wide variety of people working in the network field. It is designed for any network administrator, engineer, designer, or manager who requires a detailed knowledge of LAN switching technology.
Obviously, the book is designed to be an authoritative source for network engineers preparing for the switching portion of the CCIE exams and Cisco Career Certifications. Instead, it focuses extensively on theory and building practical knowledge.
When allied with hands-on experience, this can be a potent combination. However, this book is designed to go far beyond test preparation. It is designed to be both a tutorial and a reference tool for a wide range of network professionals, including the following:. This material then transitions smoothly into the more advanced subject matter discussed in later chapters.
For example, much of the Spanning-Tree Protocol informatio n in Part II and the real-world design information in Part V has never been published before. The Catalyst material discussed in Part VI is also completely new. Foundational Issues— This section takes you through technologies that underlie the material covered in the rest of the book.
Although advanced readers might want to skip some of this material, they are encouraged to at least skim the sections on Gigabit Ethernet and VLANs. Despite the ubiquitous deployment of this protocol, very little detailed information about its internals has been published.
This section is designed to be the most comprehensive source available on this important protocol. It presents a detailed analysis of common problems and Spanning Tree troubleshooting.
Chapter 8 begins with a detailed discussion of trunking concepts and covers Ethernet-based forms of trunking, ISL, and Advanced Features— This section begins with an in-depth discussion of the important topic of Layer 3 switching, a technology that has created a whole switching paradigm.
Both MLS routing switch and hardware-based switching router routing are examined. Real-World Campus Design and Implementation— Part V focuses on real-world issues such as design, implementation, and troubleshooting.
These chapters are oriented toward helping you benefit from the collective advice of many LAN switching experts. Catalyst Technology— This section includes a chapter that analyzes the Catalyst and models. Appendix— The single appendix in this section provides answers and solutions to the Review Questions and Hands-On Labs from the book. Where applicable, each chapter includes a variety of questions and exercises to further your knowledge of the material covered in that chapter.
Many of the questions probe at the theoretical issues that indicate your mastery of the subject matter.
Other questions and exercises provide an opportunity to build switching scenarios yourself. By utilizing extra equipment you might have available, you can build your own laboratory to explore campus switching. For those not fortunate enough to have racks of idle switching gear, the authors will be working with MentorLabs to provide value-added labs via the Internet.
Two conventions are used to draw your attention to sidebar, important, or useful information:. Various elements of Catalyst and Cisco router command syntax are presented in the course of each chapter. This book uses the same conventions as the Cisco documentation:. If you have questions, comments, or feedback, please contact the authors at the following e-mail addresses. By letting us know of any errors, we can fix them for the benefit of future generations.
Moreover, being technical geeks in the true sense of the word, we are always up for a challenging technical discussion. Kennedy Clark KClark iname. This section describes its characteristics and some of the common media options. This section describes media options and characteristics. This section provides a brief overview of Token Ring.
Since the inception of local-area networks LANs in the s, numerous LAN technologies graced the planet at one point or another. Some technologies became legends: Others became legacies: ArcNet was the basis for some of the earliest office networks in the s, because Radio Shack sold it for its personal computer line, Model II. A simple coaxial-based network, it was easy to deploy by office administrators for a few workstations.
With the higher bandwidth capacity of newer network technologies and the rapid development of higher speed workstations demanding more network bandwidth, ArcNet now fondly referred to as ArchaicNet and StarLAN were doomed to limited market presence. The legacy networks continue to find utility as distribution and backbone technologies for both manufacturing and office environments. However, the legacy systems will remain for many more years due to the existence of such a large installed base.
Users will replace Ethernet and Token Ring in phases as applications demand more bandwidth. Although Gigabit Ethernet is not yet a popular desktop technology, it is discussed here because of its relationship to Ethernet and its use in Catalyst networks for trunking Catalysts together.
This chapter also describes how the access methods operate, some of the physical characteristics of each, and various frame formats and address types.
When mainframe computers dominated the industry, user terminals attached either directly to ports on the computer or to a controller that gave the appearance of a direct connection. Each wire connection was dedicated to an individual terminal. Users entered data, and the terminal immediately transmitted signals to the host. Performance was driven by the horsepower in the hosts. If the host became overworked, users experienced delays in responses. Note, though, that the connection between the host and terminal was not the cause in the delay.
The users had full media bandwidth on the link regardless of the workload of the host device. Facility managers installing the connections between the terminal and the host experienced distance c onstraints imposed by the host's terminal line technology.
The technology limited users to locations that were a relatively short radius from the host. Further, labor to install the cables created inflated installation and maintenance expenses. Local-area networks LANs mitigated these issues to a large degree. One of the immediate benefits of a LAN was to reduce the installation and maintenance costs by eliminating the need to install dedicated wires to each user.
Instead, a single cable pulled from user to user allowed users to share a common infrastructure instead of having dedicated infrastructures for each station. A technology problem arises when users share a cable, though. Specifically, how does the network control who uses the cable and when?
Broadband technologies like cable television CATV support multiple users by multiplexing data on different channels frequencies.
For example, think of each video signal on a CATV system as a data stream. Each data stream is transported over its own channel. A CATV system carries multiple channels on a single cable and can, therefore, carry multiple data streams concurrently.
This is an example of frequency-division multiplexing FDM. The initial LANs were conceived as baseband technologies, however, which do not have multiple channels. Baseband technologies do not transmit using FDM.
Rather, they use bandwidth-sharing, which simply means that users take turns transmitting. Ethernet and Token Ring define sets of rules known as access methodsfor sharing the cable.
The access methods approach media sharing differently, but have essentially the same end goal in mind. In a meeting, all individuals have the right to speak. The unspoken rule that all follows, though, is "Only one person can talk at a time. If someone is already speaking, you must wait until they are finished. When you start to speak, you need to continue to listen in case someone else decides to speak at the same time.
If this happens, both parties must stop talking and wait a random amount of time. Only then do they have the right to start the process again. If individuals fail to observe the protocol of only one speaker at a time, the meeting quickly degenerates and no effective communication occurs.
Unfortunately, this happens all too often. In Ethernet, multiple access is the terminology for many stations attaching to the same cable and having the opportunity to transmit. No station has any priority over any other station. However, they do need to take turns per the access algorithm. Carrier sense refers to the process of listening before speaking.
The Ethernet device wishing to communicate looks for energy on the media an electrical carrier. If a carrier exists, the cable is in use and the device must wait to transmit.
Many Ethernet devices maintain a counter of how often they need to wait before they can transmit. Some devices call the counter a deferral or back-off counter. If the deferral counter exceeds a threshold value of 15 retries, the device attempting to transmit assumes that it will never get access to the cable to transmit the packet.
In this situation, the source device discards the frame. This might happen if there are too many devices on the network, implying that there is not enough bandwidth available. When this situation becomes chronic, you should segment the network into smaller segments. Chapter 2, "Segmenting LANs," discusses various approaches to segmentation. If the power level exceeds a certain threshold, that implies to the system that a collision occurred.
When stations detect that a collision occurs, the participants generate a collision enforcement signal. The enforcement signal lasts as long as the smallest frame size.
In the case of Ethernet, that equates to 64 bytes. This ensures that all stations know about the collision and that no other station attempts to transmit during the collision event. If a station experiences too many consecutive collisions, the station stops transmitting the frame. Some workstations display an error message stating Media not available. The exact message differs from implementation to implementation, but every workstation attempts to convey to the user that it was unable to send data for one reason or another.
Addressing in Ethernet How do stations identify each other? In a meeting, you identify the intended recipient by name.
You can choose to address the entire group, a set of individuals, or a specific person. Speaking to the group equates to a broadcast; a set of individuals is a multicast; and addressing one person by name is a unicast.
Most traffic in a network is unicast in nature, characterized as traffic from a specific station to another specific device. Some applications generate multicast traffic. Examples include multimedia services over LANs. These applications intend for more than one station to receive the traffic, but not necessarily all for all stations. Video conferencing applications frequently implement multicast addressing to specify a group of recipients.
Networking protocols create broadcast traffic, whereas IP creates broadcast packets for ARP and other processes. Routers often transmit routing updates as broadcast frames, and AppleTalk, DecNet, Novell IPX, and many other protocols create broadcasts for various reasons.
Figure shows a simple legacy Ethernet system with several devices attached. Each device's Ethernet adapter card has a bit 6 octet address built in to the module that uniquely identifies the station. Devices express MAC addresses as hexadecimal values. Sometimes MAC address octets are separated by hyphens - sometimes by colons: The three formats of F-4F, This book usually uses the first format because most of the Catalyst displays use this convention; however, there are a couple of exceptions where you might see the.
To help ensure uniqueness, the first three octets indicate the vendor who manufactured the interface card. Cisco has several OUI values: The last three octets of the MAC address equate to a host identifier for the device. They are locally assigned by the vendor. The combination of OUI and host number creates a unique address for that device. Each vendor is responsible to ensure that the devices it manufactures have a unique combination of 6 octets.
This is a unicast frame. Because the LAN is a shared media, all stations on the network receive a copy of the frame. Only Station 2 performs any processing on the frame, though. If they do not match, the station's interface module discards ignores the frame. This prevents the packet from consuming CPU cycles in the device. Station 2, however, sees a match and sends the packet to the CPU for further analysis. The CPU examines the network protocol and the intended application and decides whether to drop or use the packet.
Not all frames contain unicast destination addresses. Some have broadcast or multicast destination addresses. Stations treat broadcast and multicast frames differently than they do unicast frames. Stations view broadcast frames as public service announcements. When a station receives a broadcast, it means, "Pay attention! I might have an important message for you! Like unicast frames, all stations receive a frame with a broadcast destination address.
When the interface compares its own MAC address against the destination address, they don't match. Normally, a station discards the frame because the destination address does not match its own hardware address.
But broadcast frames are treated differently. Even though the destination and built-in address don't match, the interface module is designed so that it still passes the broadcast frame to the processor. This is intentional because designers and users want to receive the broadcast frame as it might have an important request or information. Unfortunately, probably only one or at most a few stations really need to receive the broadcast message. For example, an IP ARP request creates a broadcast frame even though it intends for only one station to respond.
The source sends the request as a broadcast because it does not know the destination MAC address and is attempting to acquire it. The only thing the source knows for sure when it creates the ARP request is the destination's IP address.
That is not enough, however, to address the station on a LAN. The frame must also contain the MAC address. Routing protocols sometimes use broadcast MAC addresses when they announce their routing tables. The router transmits the update in a broadcast frame. The router does not necessarily know all of the routers on the network. By sending a broadcast message, the router is sure that all routers attached to the network will receive the message. There is a downside to this, however.
All devices on the LAN receive and process the broadcast frame, even though only a few devices really needed the updates. This consumes CPU cycles in every device. If the number of broadcasts in the network becomes excessive, workstations cannot do the things they need to do, such as run word processors or flight simulators.
The station is too busy processing useless for them broadcast frames. Multicast frames differ from broadcast frames in a subtle way.
Multicast frames address a group of devices with a common interest and allow the source to send only one copy of the frame on the network, even though it intends for several stations to receive it. When a station receives a multicast frame, it compares the multicast address with its own address. Unless the card is previously configured to accept multicast frames, the multicast is discarded on the interface and does not consume CPU cycles.
This behaves just like a unicast frame. The information contained in the announcement is only interesting to other Cisco devices and the network administrator. To transfer the announcement, the Cisco source could send a unicast to each and every Cisco device. That, however, means multiple transmissions on the segment and consumes network bandwidth with redundant information. Further, the source might not know about all of the local Cisco devices and could, therefore, choose to send one broadcast frame.
All Cisco devices would receive the frame. Unfortunately, so would all non-Cisco devices. The last alternative is a multicast address. All non- Cisco devices ignore this multicast me ssage. Only routers interested in receiving the OSPF announcement configure their interface to receive the message. All other devices filter the frame. When stations transmit to each other on a LAN, they format the data in a structured manner so that devices know what octets signify what information.
Various frame formats are available. When you configure a device, you must define what format your station will use, realizing that more than one format might be configured, as is true for a router. Figure illustrates four common frame formats for Ethernet. Some users interchange the terms packets and frames rather loosely. According to RFC , a subtle difference exists. Frames refer to the entire message, from the data link layer Layer 2 header information through and including the user data.
Packets exclude Layer 2 headers and only include the IP header Layer 3 protocol header through and including user data. The frame formats developed as the LAN industry evolved and differing requirements arose for protocols. The first 6 octets contain the destination's MAC address, whereas the next field of 6 octets contain the source's MAC address.
Two bytes follow that indicate to the receiver the correct Layer 3 protocol to which the packet belongs. For example, if the packet belongs to IP, then the type field value is 0x Table lists several common protocols and their associated type values.
Table Following the type value, the receiver expects to see additional protocol headers. For example, if the type value indicates that the packet is IP, the receiver expects to decode IP headers next. If the value is , the receiver tries to decode the packet as a Novell packet. IEEE defined an alternative frame format. In the IEEE Three derivatives to this format are used in the industry: A receiver recognizes that a packet follows If the value falls within the range of 0x and 0x05DC decimal , the value indicates length; protocol type values begin after 0x05DC.
The rules constantly keep in mind the need to detect collisions and to report them to the participants. Ethernet defines a slotTime wherein a frame travels from one network extreme to the other. In Figure , assume that Station 1, located at one extreme of the network, transmits a frame.
Just before the frame reaches Station 2, located at the other extreme of the network, Station 2 transmits. Station 2 transmits because it has something to send, and because Station 1's frame hasn't arrived yet, Station 2 detects silence on the line.
This demonstrates a prime example of a collision event between devices at opposite extremes of the network. Because they are at opposite ends of the network, the timing involves worst case values for detecting and reporting collisions.
Ethernet rules state that a station must detect and report collisions between the furthest points in the network before the source completes its frame transmission. Specifically, for a legacy 10 Mbps Ethernet, this must all occur within Why The time is based on the smallest frame size for Ethernet, which corresponds to the smallest time window to detect and report collisions. The minimum frame size for Ethernet is 64 bytes, which has bits. Each bit time is 0. Therefore, the slot time for Ethernet is 0.
Next, the Ethernet specification translates the slotTime into distance. As the Ethernet signal propagates through the various components of the collision domain, time delays are introduced. Time delay values are calculated for copper cables, optical fibers, and repeaters. The amount of delay contributed by each component varies based upon the media characteristics.
A correctly designed network topology totals the delay contribution for each component between the network extremes and ensures that the total is less than one half of This guarantees that Station 2 can detect the collision and report it to Station 1 before Station 1 completes the transmission of the smallest frame.
A network that violates the slotTime rules by extending the network to distances that require more than When a station transmits, it retains the frame in a local buffer until it either transmits the frame successfully that is, without a collision or the deferral counter threshold is exceeded. We previously discussed the deferral counter situation. Assume that a network administrator overextends the network in Figure by inserting too many repeaters or by deploying segments that are too long. When Station 1 transmits, it assumes that the frame successfully transmitted if it experiences no collision by the time that it transmits 64 octets.
Once the frame believes that it was successfully transmitted, the fra me is eliminated from buffers leaving no opportunity to retry. When the network overextends the slotTime, the source might learn of a collision after it transmits the first 64 octets. But no frame is. Specifically, network administrators focus on the question, "What is the average loading that should be supported on a network? Some state as high as 50 percent.
The answer really depends upon your users' application needs. At what point do users complain? When it is most inconvenient for you to do anything about it, of course! Networks rarely support a sustained loading over 50 percent due to bandwidth loss from collisions. Collisions consume bandwidth and force stations to retransmit, consuming even more bandwidth.
If the network were collisionless, up to percent utilization could be achieved. This is not likely. To provide some guidelines though, consider the theoretical frame rates for Ethernet. Frame rates depend upon the size of the frame. To calculate the packets per second for various frame sizes, use the following formula:. This is specified as 9.
This is 6. For a octet frame, this is A 30 percent average loading implies that a network analyzer measures about 3 Mbps of sustained traffic on the system. This in and of itself is not enough to determine how well or how poorly the network is functioning.
What size packets are creating the load? Usually numerous packet sizes are involved. How many collisions are there on the network? If there are few, only some of the stations are transmitting. This might provide a clue for you that more transmitters can be supported on the network.
In any event, a good measurement is needed of your network and what users perceive the current network response to be. When Ethernet technology availed itself to users, the 10 Mbps bandwidth seemed like an unlimited resource. Yet workstations have developed rapidly since then, and applications demand more data in shorter amounts of time. When the data comes from remote sources rather than from a local storage device, this amounts to the application needing more network bandwidth.
New applications find 10 Mbps to be too slow. Consider a surgeon downloading an image from a server over a 10 Mbps shared media network. If the image is a high resolution image, not unusually on the order of MB, it could take a while to receive the image. What if the shared network makes the available user bandwidth about kbps a generous number for most networks on the average?
It could take the physician 26 minutes to download the image:. If that were you on the operating table waiting for the image to download, you would not be very happy!
If you are the hospital administration, you are exposing yourself to surgical complications at worst and idle physician time at best. Obviously, this is not a good situation. Sadly, many hospital networks function like this and consider it normal.
Clearly, more bandwidth is needed to support this application. Recognizing the growing demand for higher speed networks, the IEEE formed the Because they operate at 10 times the speed of 10 Mbps Ethernet, all timing factors reduce by a factor of For example, the slotTime for Mbps Ethernet is 5.
The IFG is. And because timing is one tenth that of 10 Mbps Ethernet, the network diameter must also shrink to avoid late collisions. An objective of the BaseX standard was to maintain a common frame format with legacy Ethernet. Therefore, BaseX uses the same frame sizes and formats as 10BaseX. Everything else scales by one tenth due to the higher data rate.
When passing frames from a 10BaseX to a BaseX system, the interconnecting device does not need to re-create the frame's Layer 2 header because they are identical on the two systems. Because of the higher signaling rate of BaseT, creating a single method to work over all cable types was not likely.
The encoding technologies that were available at the time forced IEEE to create variants of the standard to support Category 3 and 5 cables. A fiber optic version was created as well. When a station talks, all other devices must listen or else the system experiences a collision.
In a 10 Mbps system, the total bandwidth available is dedicated to transmitting or receiving depending upon whether the station is the source or the recipient. This describes half duplex. The original LAN standards operate in half-duplex mode allowing only one station to transmit at a time. This was a side effect of the bus topology of 10Base5 and 10Base2 where all stations attached to the same cable.
With the introduction of 10BaseT, networks deployed hubs and attached stations to the hub on dedicated point-to-point links.
Stations do not share the wire in this topology. Because each link is not shared, a new operational mode becomes feasible. Rather than running in half-duplex mode, the systems can operate in full-duplex mode, which allows stations to transmit and receive at the same time, eliminating the need for collision detection.
What advantage does this provide? The tremendous asset of the precious network commodity—bandwidth. When a station operates in full-duplex mode, the station transmits and receives at full bandwidth in each direction. The most bandwidth that a legacy Ethernet device can expect to enjoy is 10 Mbps. It either listens at 10 Mbps or transmits at 10 Mbps. In contrast, a BaseX device operating in full-duplex mode sees Mbps of bandwidth— Mbps for transmitting and Mbps for receiving.
Users upgraded from 10BaseT to BaseX have the potential to immediately enjoy a twentyfold, or more, bandwidth improvement. If the user previously attached to a shared 10 Mbps system, they might only practically enjoy a couple megabits per second of effective bandwidth. Upgrading to a full duplex Mbps system might provide a perceived one hundredfold improvement. If your users are unappreciative of the additional bandwidth, you have an unenviable group of colleagues with which to work.
Put them back on 10BaseT! Be aware, however: Just because an interface card runs BaseX full duplex, you cannot assume that the device where you install it supports full-duplex mode. In fact, some devices might actually experience worse throughput when in full-duplex mode than when in half-duplex mode.
For example, Windows NT 4. The IEEE This allows a receiver to send a special frame back to the source whenever the receiver's buffers overflow. The receiver sends a special packet called a pause frame. In the frame, the receiver can request the source to stop sending for. If the receiver can handle incoming traffic again before the timer value in the pause frame expires, the receiver can send another pause frame with the timer set to zero.
This tells the receiver that it can start sending again. Although BaseX supports both full- and half-duplex modes, you can deploy Mbps hubs that operate in half-duplex mode. That means the devices attached to the hub share the bandwidth just like the legacy Ethernet systems. In this case, the station must run in half-duplex mode. To run in full-duplex mode, the device and the hub switch must both support and be configured for full duple x.
Note that you cannot have a full duplex for a shared hub. If the hub is shared, it must operate in half-duplex mode. Autonegotiation With the multiple combinations of network modes available, configuring devices gets confusing. You need to determine if the device needs to operate at 10 or Mbps, whether it needs to run in half- or full-duplex mode, and what media type to use. The device configuration must match the hub configuration to which it attaches.
Autonegotiation attempts to simplify manual configuration requirements by enabling the device and hub to automatically agree upon the highest common operational level. The The other end also transmits FLP announcements, and the two ends settle on whatever method has highest priority in common between them. Table illustrates the priority scheme. According to Table , BaseT2 full-duplex mode has highest priority, whereas the slowest method, 10BaseT half-duplex, has lowest priority.
Priority is determined by speed, cable types supported, and duplex mode. A system always prefers Mbps over 10 Mbps, and always prefers full duplex over half duplex. This is not a direct result of BaseT2 being a more recent medium.
Not all devices perform autonegotiation. We have observed at several customer locations failure of the autonegotiation process—either because of equipment not supporting the feature or poor implementations.
The devices use two pairs of the cable: This encoding scheme adds a fifth bit for every four bits of user data.
That means there is a 25 percent overhead in the transmission to support the encoding. We try not to tell this to marketing folks so that they do not put on their data sheets Mbps throughput!
Some use Category 3.
Category 3 cable was installed in many locations to support voice transmission and is frequently referred to as voice grade cable. It is tested for voice and low speed data applications up to 16 MHz. Category 5 cable, on the other hand, is intended for data applications and is tested at MHz. As with 10BaseT, BaseT4 links work up to meters. To support the higher data rates, though, BaseT4 uses more cable pairs.
Three pairs support transmission and one pair supports collision detection. Another technology aspect to support the high data rates over a lower bandwidth cable comes from the encoding technique used for BaseT4. Most Category 3 cable installations intend for the cable to support voice communications.
By consuming all the pairs in the cable for data transmissions, no pairs remain to support voice communications. A new addition to the BaseT standards, BaseT2 relies upon advanced digital signal processing chips and encoding.
When should you use the fiber optic version? One clear situation arises when you need to support distances greater than meters. Multimode supports up to 2, meters in full-duplex mode, meters in half- duplex mode. Single- mode works up to 10 kms—a significant distance advantage. Other advantages of fiber include its electrical isolation properties. For example, if you need to install the cable in areas where there are high levels of radiated electrical noise near high voltage power lines or transformers , fiber optic cable is best.
The cable's immunity to electrical noise makes it ideal for this environment. If you are installing the system in an environment where lightning frequently damages equipment, or where you suffer from ground loops between buildings on a campus, use fiber.
Fiber optic cable carries no electrical signals to damage your equipment. Note that the multimode fiber form of BaseFX specifies two distances. If you run the equipment in half-duplex mode, you can only transmit meters. Full-duplex mode reaches up to 2 kms. Media-Independent Interface MII When you order networking equipment, you usually order the system with a specific interface type. For example, you can purchase a router with a BaseTX connection. When you buy it with this kind of interface, the BaseTX transceiver is built in to the unit.
This connection is fine, as long as you only attach it to another BaseTX device such as another workstation, hub, or switch. What if you decide at a later time that you need to move the router to another location, but the distance demands that you need to connect over fiber optics rather than over copper?
This can be costly. An alternative is the MII connector. This is a pin connector that allows you to connect an external transceiver that has an MII connection on one side and a BaseX interface on the other side. Functionally, it is similar to the AUI connector for 10 Mbps Ethernet and allows you to change the media type without having to replace any modules. Rather, you can change a less expensive media adapter transceiver.
For Fast Ethernet, if you decide to change the interface type, all you need to do is change the MII transceiver. This is potentially a much less expensive option than replacing an entire router module. Network Diameter Designing with Repeaters in a BaseX Network In a legacy Ethernet system, repeaters extend cable distances, allowing networks to reach further than the segment length.
For example, a 10Base2 segment only reaches meters in length. If an administrator desires to attach devices beyond this reach, the administrator can use repeaters to connect a second section of 10Base2 cable to the first. In a 10BaseT network, hubs perform the repeater functions allowing two meter segments to connect together. The two repeater classes differ in their latency which affects the network diameter supported. A Class I repeater latency is 0.
Why are there two repeater classes? Class I repeaters operate by converting the incoming signal from a port into an internal digital signal. It then converts the frame back into an analog signal when it sends it out the other ports. Remember that the line encoding scheme for these methods differ. A Class I repeater can translate the line encoding to support the differing media types.
Class II repeaters, on the other hand, are not as sophisticated. They can only support ports with a same line encoding method.
The lower latency value for a Class II repeater enables it to support a slightly larger network diameter than a Class I based network. Converting the signal from analog to digital and performing line encoding translation consumes bit times. A Class I repeater therefore introduces more latency than a Class II repeater reducing the network diameter.
Figure illustrates interconnecting stations directly together without the use of a repeater. Each station is referred to as a DTE data terminal equipment device. Transceivers and hubs are DCE data communication equipment devices. Either copper or fiber can be used. Be sure, however, that you use a cross-over cable in this configuration. A cross-over cable attaches the transmitter pins at one end to the receiver pins at the other end. If you use a straight through cable, you connect "transmit" at one end to "transmit" at the other end and fail to communicate.
The Link Status light does not illuminate! There is an exception to this where you can, in fact, connect two DTE or two DCE devices directly together with a straight through cable. The MDIX is a media interface cross-over port. Most ports on devices are MDI. Using a Class I repeater as in Figure enables you to extend the distance between workstations.
Note that with a Class I repeater you can mix the types of media attaching to the repeater. Only one Class I repeater is allowed in the network. To connect Class I repeaters together, a bridge, switch, or router must connect between them. Class II repeaters demand homogenous cabling to be attached to them. If you use BaseT4, all ports must be BaseT4.
Figure illustrates a network with only one Class II repeater. The connection between the repeaters must be less than or equal to five meters. Why daisy chain the repeaters if it only gains five meters of distance? Simply because it increases the number of ports available in the system.
The networks in Figure through Figure illustrate networks with repeaters operating in half-duplex mode. The network diameter constraints arise from a need to honor the slotTime window for BaseX half-duplex networks.
Extending the network beyond this diameter without using bridges, switches, or routers violates the maximum extent of the network and makes the network susceptible to late collisions. This is a bad situation. The network in Figure demonstrates a proper use of Catalyst switches to extend a network. Practical Considerations BaseX networks offer at least a tenfold increase in network bandwidth over shared legacy Ethernet systems. In a full-duplex network, the bandwidth increases by twentyfold.
Is all this bandwidth really needed? After all, many desktop systems cannot generate anywhere near Mbps of traffic. Most network systems are best served by a hybrid of network technologies.
Some users are content on a shared 10 Mbps system. These users normally do little more than e-mail, Telnet, and simple Web browsing. The interactive applications they use demand little network bandwidth and so the user rarely notices delays in usage.
Of the applications mentioned for this user, Web browsing is most susceptible because many pages incorporate graphic images that can take some time to download if the available network bandwidth is low.
If the user does experience delays that affect work performance as opposed to non- work-related activities , you can increase the users bandwidth by doing the following:. Which of these is most reasonable? It depends upon the user's application needs and the workstation capability.
If the user's applications are mostly interactive in nature, either of the first two options can suffice to create bandwidth. However, if the user transfers large files, as in the case of a physician retrieving medical images, or if the user frequently needs to access a file server, BaseX full duplex might be most appropriate.
Option 3 should normally be reserved for specific user needs, file servers, and routers. Another appropriate use of Fast Ethernet is for backbone segments. A corporate network often has an invisible hierarchy where distribution networks to the users are lower speed systems, whereas the networks interconnecting the distribution systems operate at higher rates.
This is where Fast Ethernet might fit in well as part of the infrastructure. The decision to deploy Fast Ethernet as part of the infrastructure is driven by corporate network needs as opposed to individual user needs, as previously considered. Chapter 8, "Trunking Technologies and Applications," considers the use of Fast Ethernet to interconnect Catalyst switches together as a backbone.
As if Mbps is not enough, yet another higher bandwidth technology was unleashed on the industry in June of We discussed earlier how stations are hard-pressed to fully utilize Mbps Ethernet. Why then do we need a Gigabit bandwidth technology?
Gigabit Ethernet proponents expect to find it as either a backbone technology or as a pipe into very high speed file servers. This contrasts with Fast Ethernet in that Fast Ethernet network administrators can deploy Fast Ethernet to clients, servers, or use it as a backbone technology. Gigabit Ethernet will not be used to connect directly to clients any time soon. Some initial studies of Gigabit Ethernet indicate that installing Mbps interfaces in a Pentium class workstation will actually slow down its performance due to software interrupts.
On the other hand, high performance UNIX stations functioning as file servers can indeed benefit from a larger pipe to the network. In addition to the practical discussion of advanced switching issues, this book also contains case studies that highlight real-world design, implementation, and management issues, as well as chapter-ending review questions and exercises.
This book is part of the Cisco CCIE Professional Development Series from Cisco Press, which offers expert-level instruction on network design, deployment, and support methodologies to help networking professionals manage complex networks and prepare for CCIE exams.
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