CCIE Professional Development: Cisco LAN Switching is essential for preparation for the CCIE Routing and Switching exam track. As well as CCIE preparation. Cisco LAN Switching (CCIE Professional Development series) · Read more Cisco LAN Switching Configuration Handbook, Second Edition · Read more. The essential guide for understanding Ethernet switched networks Understand various Ethernet technologies from 10BASE-T to Gigabit Ethernet Learn about.
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Parkhurst Cisco Multicast Routing and Switching .. We have seen Ethernet become the dominant local-area networking (LAN) medium. With the. The most complete guide to Cisco Catalyst(r) switch network design, operation, and configuration Master key foundation topics such as. Cisco Press CCIE Routing and Switching v Official Cert Guide Vol. 1 5th Cisco LAN Switching Configuration Handbook, Second Edition.
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.
Cisco LAN Switching
Configuring the Catalyst. Errata - 21 KB -- Errata. Get unlimited day access to over 30, books about UX design, leadership, project management, teams, agile development, analytics, core programming, and so much more. All rights reserved. Join Sign In. View Larger Image.
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.
Cisco LAN switching fundamentals
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 : and sometimes periods. The three formats of F-4F, F:4F, and 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 13 second or third format.
Do not let this confuse you. They all represent MAC addresses. Figure A Simple Ethernet Network To help ensure uniqueness, the first three octets indicate the vendor who manufactured the interface card. 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. The CPU examines the network protocol and the intended application and decides whether to drop or use the packet. Broadcast Frames 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.
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 download a router with a BaseTX connection.
When you download 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.
CCIE® Professional Development Cisco LAN Switching - 1st Edition
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 a Catalyst network, Gigabit Ethernet interconnects Catalysts to form a high-speed backbone.
The Catalysts in Figure have low speed stations connecting to them 10 and Mbps , but have Mbps to pass traffic between workstations. A file server in the network also benefits from a Mbps connection supporting more concurrent client accesses. Gigabit Architecture Gigabit Ethernet merges aspects of The Fiber Channel standard details a layered network model capable of scaling to bandwidths of 4 Gbps and to extend to distances of 10 kms.
Gigabit Ethernet borrows the bottom two layers of the standard: FC-0 and FC-1 replace the physical layer of the legacy Figure illustrates the merger of the standards to form Gigabit Ethernet.
The Fiber Channel standard incorporated by Gigabit Ethernet transmits at 1. Gigabit Ethernet increases the signaling rate to 1. This encoding technique simplifies fiber optic designs at this high data rate. The ST, or snap and twist, style connectors previously preferred were a bayonet type connector and required finger space on the front panel to twist the connector into place.
The finger space requirement reduced the number of ports that could be built in to a module. A new connector type, the MT-RJ, is now finding popularity in the fiber industry. Further, its smaller size allows twice the port density on a face plate than ST or SC connectors. These are derived from the smallest frame size of 64 octets. In the BaseX network, the slot-time translates into a network diameter of about meters.
If the same frame size is used in Gigabit Ethernet, the slotTime reduces to. This is close to unreasonable.
Therefore, The carrier extension process increases the slotTime value to bits or 4. The transmitting station expands the size of the transmitted frame to ensure that it meets the minimal slotTime requirements by adding non-data symbols after the FCS field of the frame.
Not all frame sizes require carrier extension. This is left as an exercise in the review questions. The 8B10B encoding scheme used in Gigabit Ethernet defines various combinations of bits called symbols.
Some symbols signal real data, whereas the rest indicate non-data. The station appends these non- data symbols to the frame. The receiving station identifies the non-data symbols, strips off the carrier extension bytes, and recovers the original message. Figure shows the anatomy of an extended frame.
The addition of the carrier extension bits does not change the actual Gigabit Ethernet frame size. The receiving station still expects to see no fewer than 64 octets and no more than octets. The fiber optic options vary for the size of the fiber and the modal bandwidth. Table summarizes the options and the distances supported by each.
This results from the interaction of the light with the fiber cable at this wavelength. Why use BaseSX then? Because the components are less expensive than for BaseLX. Use this less expensive method for short link distances for example, within an equipment rack. Wavelength correlates to the frequency of RF systems. In the case of optics, we specify the wavelength rather than frequency.
In practical terms, this corresponds to the color of the light. Typical wavelengths are nanometers nms and nms. In fact, the L of LX stands for long wavelength. Be careful when using fiber optic systems. Do not look into the port or the end of a fiber!
It can be hazardous to the health of your eye. Use the LX option for longer distance requirements. If you need to use single mode, you must use the LX. Not included in Table is a copper media option. This new cable type is not well-known in the industry, but is necessary to support the high-bandwidth data over copper. It is intended to be used to interconnect devices collocated within an equipment rack very short distances apart. This is appropriate when Catalysts are stacked in a rack and you want a high speed link between them, but you do not want to spend the money for fiber optic interfaces.
One final copper version is the BaseT standard which uses Category 5 twisted- pair cable. It supports up to meters, but uses all four pairs in the cable. This standard is under the purview of the IEEE Multiple stations attach to a network and share the bandwidth. The 4 Mbps version represents the original technology released by IBM. With a GBIC interface. A Gigabit Ethernet Interface Converter GBIC is similar to an MII connector described in the Fast Ethernet section and allows a network administrator to configure an interface with external components rather than downloading modules with a built-in interface type.
GBIC transceivers have a common connector type that attaches to the Gigabit device. Figure illustrates a logical representation of a Token Ring system.
Token Ring supports two bandwidth options: To this point.
Token Ring passes a token on the network that authorizes the current holder to transmit onto the cable. Token Ring Operations To control access onto the system. This section briefly examines Token Ring. Token Ring systems. The frame eventually returns to the source. Depending upon the length of the ring.
Each station in the network creates a break in the ring. Each station locally copies the frame and passes it to the next station.
Station 1. During the time between the completion of transmission and the removal of the frame. Early token release. The frame circulates around the ring from station to station. Some network inefficiencies result. The source is responsible for removing the frame and introducing a new token onto the network. All stations receive a copy of the frame because. Assume Station 1 wants to transmit to Station 3. If a station desires to send information.
Each station compares the destination MAC address against its own hardware address and either discards the frame if they don't match. This amounts to wasted bandwidth on the network. A token passes around the ring from station to station. Token Ring is a broadcast network. When Station 2 receives the frame. In this model. To prevent this. This continues between all attached stations until the ring is completed. Whenever a packet circulates around the ring.
The hub. This consumes bandwidth on the network and prevents other stations from generating traffic. This increases the Token Ring utilization to a much higher degree than for systems without early token release.
This prevents the source from removing the frame and causes it to circulate around the network—possibly indefinitely. Token Ring Components Token Ring systems use a hub architecture to interconnect stations. A lot of 10 Mbps systems still exist with varied media options such as copper and fiber. You should expect to encounter this type of connection method for at least another few years. What happens if a user detaches a station? When this occurs. A network administrator can daisy-chain MAUs together to extend the distance and to introduce more ports in the network.
Cisco LAN Switching (CCIE Professional Development series)
This chapter covered the basics of how legacy Ethernet functions. Review Questions 1: What is the pps rate for a BaseX network?
Calculate it for the minimum and maximum frame sizes. What are the implications of mixing half-duplex and full-duplex devices? How do you do it? In the opening section on Fast Ethernet. With the capability to run in full-duplex modes. And for real bandwidth consumers. What is an approximate download time for the image over a half-duplex BaseX system?
Over a full-duplex BaseX system? What disadvantages are there in having an entire network running in BaseX full-duplex mode? Why or why not? What is the smallest Gigabit Ethernet frame size that does not need carrier extension?
This chapter covered some of the attributes of Gigabit Ethernet and choices available to you for media. This chapter discussed the media options available for Fast Ethernet and some of the operational characteristics of it. Gigabit Ethernet offers even more capacity to meet the needs of trunking switches together and to feed high performance file servers.
Fast Ethernet offers significant bandwidth leaps to meet the needs of many users. Because of the limitations that legacy Ethernet can cause some applications. If users currently attach to a legacy 10 Mbps network. Management wants more users on the network. It also describes why network administrators segment LANs.
From a network administrator's point of view. As corporations grow. A straightforward technology answer might include the deployment of a higher speed network.
From a corporate point of view. Although this book cannot help with the last issue. This chapter.
Why Segment LANs? Network designers often face a need to extend the distance of a network. Segmenting LANs This chapter covers the following key topics: To further confuse the issue. Even so. As the foundational technology for LAN switches. Engineers often exhibit some confusion about which component to use for various network configurations. Chapter 2.
Changing the network infrastructure in this way means replacing workstation adapter cards with ones capable of Mbps.
Each component serves specific roles and has utility when properly deployed. Network engineers building LAN infrastructures can choose from many internetworking devices to extend networks: It also means replacing the hubs to which the A good understanding of how these devices manipulate collision and broadcast domains helps the network engineer to make intelligent choices.
The new hubs must also support the new network bandwidth. The after network replaces the repeaters with bridges and routers isolating segments and providing more bandwidth for users. By reducing the number of users on each segment.
The sections on LAN segmentation with bridges and routers later in this chapter define collision and broadcast domains and describe why this is so. The extreme case dedicates one user to each segment providing full media bandwidth to each user. The question remains. Figure illustrates a before-and-after situation for segmenting networks. Should you use a repeater. Segmenting LANs is another approach to provide users additional bandwidth without replacing all user equipment.
This is exactly what switches allow the administrator to build. Bridges and routers generate bandwidth by creating new collision and broadcast domains as summarized in Table Although effective. The next section in this chapter describes how repeaters work and why this is true. By segmenting LANs. They simply allow you to They blindly perform their responsibility of forwarding signals from one wire to all other wires.
Although Figure shows the interconnection of two segments. If the frame contains errors. The sections that follow describe the various options. Repeaters truly act like an extension of the cable. If a collision occurs on Wire A. A repeater attaches wire segments together as shown in Figure The repeater is included in the discussion because you might attach a repeater-based network to your segmented network.
Workstations have no knowledge of the presence of a repeater which is completely transparent to the attached devices. Figure A Multiport Repeater If the frame violates the minimum or maximum frame sizes specified by Ethernet. When Station 1 transmits to Station 2. Wire B also sees it.
Repeaters operate at Layer 1 of the OSI model and appear as an extension to the cable segment. Repeaters are unintelligent devices and have no insight to the data content.
If Stations 1 and 2 in Figure participate in a collision. They become additional participants in the collision. Repeaters strip all eight preamble bytes from the incoming frame.
If Stations 3 and 4 do not know of the collision. A 10BaseT network is comprised of hubs and twisted-pair cables to interconnect workstations. As in Figure They arise from different causes and must be considered when extending a network with repeaters. Repeaters perform several duties associated with signal propagation. Preamble bits precede the frame destination MAC address and help receivers to synchronize. The 8-byte preamble has an alternating binary pattern except for the last byte.
Hubs are multiport repeaters and forward signals from one interface to all other interfaces. The last two bits indicate to the receiver that data follows. The last byte of the preamble. Limitations exist in a repeater-based network. Stations on Wire B must wait for the collision to clear before transmitting. The limitations include the following: Repeaters also ensure that collisions are signaled on all ports. Collisions extend through a repeater and consume bandwidth on all interconnected segments.
It behooves the network administrator to determine bandwidth requirements for user applications and to compare them against the theoretical bandwidth available in the network. This is true whether the source frame is unicast. As a theoretical extreme. If the impedance changes too much. Another side effect of a collision domain is the propagation of frames through the network.
All stations see all frames. In this case. The limitation is inherent in the bus architectures of 10Base2 and 10Base5 networks. If the network uses shared network technology.
Ethernet imposes limits on how many workstations can attach to a cable. This helps to determine by how much you need to increase the network's capacity to support the applications. Legacy Ethernet systems have a shared 10 Mbps bandwidth. Use a network analyzer to measure the average and peak bandwidth consumed by the applications. Adding more stations to the repeater network potentially divides the bandwidth even further.
Simply attaching a station does not consume bandwidth until the device transmits. Number of Stations per Segment Further. Repeaters cannot increase the number of stations supported per segment. Collisions on one segment affect stations on another repeater-connected segment. The stations take turns using the bandwidth.
As the number of transceivers attached to a cable increases.Number of Stations per Segment Further. This is the bridge learningprocess. Using a Class I repeater as in Figure enables you to extend the distance between workstations. Each broadcast domain equates to a VLAN. It also describes why network administrators segment LANs.
In a meeting, all individuals have the right to speak. The last three octets of the MAC address equate to a host identifier for the device.
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