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 most complete guide to Cisco Catalyst(r) switch network design, operation, and configuration Master key foundation topics such as.
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CCIE® Professional Development Cisco LAN Switching - 1st Edition - Free ebook download as PDF File .pdf), Text File .txt) or read book online for free. Cisco Press CCIE Routing and Switching v Official Cert Guide Vol. 1 5th Cisco LAN Switching Configuration Handbook, Second Edition. DownloadCisco lan switching ccie professional development series pdf. Free. Pdf Download Creative web camera drivers model pd write Twitter for.
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. 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 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.
With a GBIC interface, the administrator has flexibility to change the interface depending upon his needs. GBIC transceivers have a common connector type that attaches to the Gigabit device, and the appropriate media connector for the media selected: This chapter began with an overview of LAN access methods.
Token Ring systems, like Ethernet, use a shared media technology. Multiple stations attach to a network and share the bandwidth.
Token Ring supports two bandwidth options: The 4 Mbps version represents the original technology released by IBM. Token Ring Operations To control access onto the system, Token Ring passes a token on the network that authorizes the current holder to transmit onto the cable.
Figure illustrates a logical representation of a Token Ring system. Each station in the network creates a break in the ring. A token passes around the ring from station to station.
If a station desires to send information, it holds onto the token and starts to transmit onto the cable. Assume Station 1 wants to transmit to Station 3.
Station 1, when it receives a token, possesses the token and transmits the frame with Station 3's MAC address as the destination and Station 1's MAC address as the sourc e. The frame circulates around the ring from station to station. Each station locally copies the frame and passes it to the next station.
Each station compares the destination MAC address against its own hardware address and either discards the frame if they don't match, or sends the frame to the processor.
When Station 2 receives the frame, it too copies the frame and sends it on to the next station. All stations receive a copy of the frame because, just like Ethernet, Token Ring is a broadcast network. The frame eventually returns to the source. The source is responsible for removing the frame and introducing a new token onto the network.
In this model, only one station at a time transmits because only one station can possess the token at a time. Some network inefficiencies result, however, when a station retains the token until it removes the frame it transmitted from the ring.
Depending upon the length of the ring, a station can complete transmission of a frame before the frame returns back to the source.
During the time between the completion of transmission and the removal of the frame, the network remains idle— no other station can transmit. This amounts to wasted bandwidth on the network. Early token release, an optional feature introduced with 16 Mbps Token Ring, permits the source to create a new token after it completes transmission, and before it. This increases the Token Ring utilization to a much higher degree than for systems without early token release.
Occasionally, a source might not be online whenever the frame it transmitted returns to it. This prevents the source from removing the frame and causes it to circulate around the network—possibly indefinitely.
This consumes bandwidth on the network and prevents other stations from generating traffic. To prevent this, one of the stations on the ring is elected to be the ring monitor. Whenever a packet circulates around the ring, the ring monitor marks a particular bit in the frame indicating, "I already saw this fra me once. Token Ring Components Token Ring systems use a hub architecture to interconnect stations.
The hub, called a multistation access unit MAU , creates a logical ring from the star attached stations as shown in Figure Internal to the MAU, the transmit from one station connects to the receive of another station. This continues between all attached stations until the ring is completed. What happens if a user detaches a station? When this occurs, the MAU bypasses the unused port to maintain ring integrity.
A network administrator can daisy-chain MAUs together to extend the distance and to introduce more ports in the network. Although many of you use a number of different LAN technologies, the market still has a preponderance of legacy Ethernet deployed.
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. This chapter covered the basics of how legacy Ethernet functions.
Because of the limitations that legacy Ethernet can cause some applications, higher speed network technologies had to be developed. With the capability to run in full-duplex modes, Fast Ethernet offers significant bandwidth leaps to meet the needs of many users. This chapter discussed the media options available for Fast Ethernet and some of the operational characteristics of it. And for real bandwidth consumers, Gigabit Ethernet offers even more capacity to meet the needs of trunking switches together and to feed high performance file servers.
This chapter covered some of the attributes of Gigabit Ethernet and choices available to you for media. 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, we discussed the download time for a typical medical image over a shared legacy Ethernet system.
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? What is the smallest Gigabit Ethernet frame size that does not need carrier extension? As the foundational technology for LAN switches, this section describes the benefits and limitations of bridges.
As corporations grow, network administrators find themselves deep in frustration. Management wants more users on the network, whereas users want more bandwidth. To further confuse the issue, finances often conflict with the two objectives, effectively limiting options. Although this book cannot help with the last issue, it can help clarify what technology options exist to increase the number of users served while enhancing the available bandwidth in the system.
Network engineers building LAN infrastructures can choose from many internetworking devices to extend networks: Each component serves specific roles and has utility when properly deployed. Engineers often exhibit some confusion about which component to use for various network configurations.
A good understanding of how these devices manipulate collision and broadcast domains helps the network engineer to make intelligent choices. Further, by understanding these elements, discussions in later chapters about collision and broadcast domains have a clearer context.
This chapter, therefore, defines broadcast and collision domains and discusses the role of repeaters, bridges, routers, and switches in manipulating the domains. It also describes why network administrators segment LANs, and how these devices facilitate segmentation.
Network designers often face a need to extend the distance of a network, the number of users on the system, or the bandwidth available to users.
From a corporate point of view, this is a good thing, because it might indicate growth. From a network administrator's point of view, this is often a bad thing, implying sleepless nights and no weekends.
Even so, how does an administrator keep everyone happy while maintaining personal sanity? A straightforward technology answer might include the deployment of a higher speed network. If users currently attach to a legacy 10 Mbps network, you could deploy a Fast Ethernet network and provide an immediate tenfold improvement in bandwidth.
Changing the network infrastructure in this way means replacing workstation adapter cards with ones capable of Mbps. It also means replacing the hubs to which the. The new hubs must also support the new network bandwidth. Although effective, a wholesale upgrade might be cost prohibitive. Segmenting LANs is another approach to provide users additional bandwidth without replacing all user equipment.
By segmenting LANs, the administrator breaks a network into smaller portions and connects them with some type of internetworking equipment. Figure illustrates a before-and-after situation for segmenting networks.
Before segmentation, all users share the network's 10 Mbps bandwidth because the segments interconnect with repeaters.
The next section in this chapter describes how repeaters work and why this is true. The after network replaces the repeaters with bridges and routers isolating segments and providing more bandwidth for users.
Bridges and routers generate bandwidth by creating new collision and broadcast domains as summarized in Table The sections on LAN segmentation with bridges and routers later in this chapter define collision and broadcast domains and describe why this is so. Each segment can further divide with additional bridges, routers, and switches providing even more user bandwidth. By reducing the number of users on each segment, more bandwidth avails itself to users.
The extreme case dedicates one user to each segment providing full media bandwidth to each user. This is exactly what switches allow the administrator to build. The question remains, though, "What should you use to segment the network? Should you use a repeater, bridge, router, or LAN switch? They simply allow you to. Bridges, routers, and switches are more suitable for LAN segmentation.
The sections that follow describe the various options. The repeater is included in the discussion because you might attach a repeater-based network to your segmented network. Therefore, you need to know how repeaters interact with segmentation devices. Repeaters operate at Layer 1 of the OSI model and appear as an extension to the cable segment.
Workstations have no knowledge of the presence of a repeater which is completely transparent to the attached devices. A repeater attaches wire segments together as shown in Figure Repeaters regenerate the signal from one wire on to the other.
When Station 1 transmits to Station 2, the frame also appears on Wire B, even though the source and destination device coexist on Wire A. Repeaters are unintelligent devices and have no insight to the data content. They blindly perform their responsibility of forwarding signals from one wire to all other wires.
If the frame contains errors, the repeater forwards it. If the frame violates the minimum or maximum frame sizes specified by Ethernet, the repeater forwards it. If a collision occurs on Wire A, Wire B also sees it. Repeaters truly act like an extension of the cable. Although Figure shows the interconnection of two segments, repeaters can have many ports to attach multiple segments as shown in Figure A 10BaseT network is comprised of hubs and twisted-pair cables to interconnect workstations.
Hubs are multiport repeaters and forward signals from one interface to all other interfaces. As in Figure , all stations attached to the hub in Figure see all traffic, both the good and the bad.
Repeaters perform several duties associated with signal propagation. For example, repeaters regenerate and retime the signal and create a new preamble. 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. The last byte of the preamble, which ends in a binary pattern of , is called the start of frame delimiter SFD. The last two bits indicate to the receiver that data follows. Repeaters strip all eight preamble bytes from the incoming frame, then generate and prepend a new preamble on the frame before transmission through the outbound interface.
Repeaters also ensure that collisions are signaled on all ports. If Stations 1 and 2 in Figure participate in a collision, the collision is enforced through the repeater so that the stations on Wire B also know of the collision. Stations on Wire B must wait for the collision to clear before transmitting.
If Stations 3 and 4 do not know of the collision, they might attempt a transmission during Station 1 and 2's collision event. They become additional participants in the collision. Limitations exist in a repeater-based network. They arise from different causes and must be considered when extending a network with repeaters. The limitations include the following:. Shared Bandwidth A repeater extends not just the distance of the cable, but it also extends the collision domain.
Collisions on one segment affect stations on another repeater-connected segment. Collisions extend through a repeater and consume bandwidth on all interconnected segments. Another side effect of a collision domain is the propagation of frames through the network.
If the network uses shared network technology, all stations in the repeater-based network share the bandwidth. This is true whether the source frame is unicast, multicast, or broadcast.
All stations see all frames. Adding more stations to the repeater network potentially divides the bandwidth even further. Legacy Ethernet systems have a shared 10 Mbps bandwidth. The stations take turns using the bandwidth. As the number of transmitting workstations increases, the amount of available bandwidth decreases. Bandwidth is actually divided by the number of transmitting stations. Simply attaching a station does not consume bandwidth until the device transmits.
As a theoretical extreme, a network can be constructed of 1, devices with only one device transmitting and the other only listening. In this case, the bandwidth is dedicated to the single transmitting station by virtue of the fact that no other device is transmitting. Therefore, the transmitter never experiences collisions and can transmit whenever it desires at full media rates.
It behooves the network administrator to determine bandwidth requirements for user applications and to compare them against the theoretical bandwidth available in the network, as well as actual bandwidth available. Use a network analyzer to measure the average and peak bandwidth consumed by the applications.
This helps to determine by how much you need to increase the network's capacity to support the applications. Number of Stations per Segment Further, Ethernet imposes limits on how many workstations can attach to a cable. These constraints arise from electrical considerations. As the number of transceivers attached to a cable increases, the cable impedance changes and creates electrical reflections in the system. If the impedance changes too much, the collision detection process fails. Limits for legacy systems, for example, include no more than attached devices per segment for a 10Base5 network.
A 10Base2 system cannot exceed 30 stations. Repeaters cannot increase the number of stations supported per segment. The limitation is inherent in the bus architectures of 10Base2 and 10Base5 networks.
End-to-End Distance Another limitation on extending networks with repeaters focuses on distance. An Ethernet link can extend only so far before the media slotTime specified by Ethernet standards is violated. As described in Chapter 1, the slotTime is a function of the network data rate. A 10 Mbps network such as 10BaseT has a slotTime of A Mbps network slotTime is one tenth that of 10BaseT. The calculated network extent takes into account the slotTime size, latency through various media such as copper and fiber, and the number of repeaters in a network.
This rule states that up to five segments can be interconnected with repeaters. But only three of the segments can have devices attached. The other two segments interconnect segments and only allow repeaters to attach at the ends. A collision in the network propagates through all repeaters to all other segments. Repeaters, when correctly used, extend the collision domain by interconnecting segments at OSI Layer 1. Any transmission in the collision domain propagates to all other stations in the network.
If the network needs to extend beyond these limits, other internetworking device types must be used. For example, the administrator could use a bridge or a router. Repeaters extend the bounds of broadcast and collision domains, but only to the extent allowed by media repeater rules. The maximum geographical extent, constrained by the media slotTime value, defines the collision domain extent.
If you extend the collision domain beyond the bounds defined by the media, the network cannot function correctly.
In the case of Ethernet, it experiences late collisions if the network extends too far. Late collision events occur whenever a station experiences a collision outside of the Figure illustrates the boundaries of a collision domain defined by the media slotTime.
All segments connected together by repeaters belong to the same collision domain. Figure also illustrates the boundaries of a broadcast domain in a repeater-based network.
Broadcast domains define the extent that a broadcast propagates throughout a network. The stations must belong to the same subnetwork as there is no router in the network.
The ARP frame is a broadcast that traverses the entire segment and transparently passes through all repeaters in the network. All stations receive the broadcast and therefore belong to the same broadcast domain. Station 2 sends a unicast reply to Station 1. All stations receive the reply because they all belong to the same collision domain although it is handled by the NIC hardware as discussed in Chapter 1.
As discussed in the previous section, Ethernet rules limit the overall distance a network segment extends and the number of stations attached to a cable segment. What do you do if you need to go further or add more devices?
Bridges provide a possible solution. 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.
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 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. Divided into six parts, this book takes you beyond basic switching concepts by providing an array of proven design models, practical implementation solutions, and troubleshooting strategies.
Part I discusses important foundation issues that provide a context for the rest of the book, including Fast and Gigabit Ethernet, routing versus switching, the types of Layer 2 switching, the Catalyst command-line environment, and VLANs.
Part V covers real-world campus design and implementation issues, allowing you to benefit from the collective advice of many LAN switching experts. 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.
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.