CHAPTERTWO: CHAPTER TWO Network Devices


Objectives: Objectives Explain the uses, advantages, and disadvantages of repeaters Explain the uses, advantages, and disadvantages of hubs Define network segmentation Explain network segmentation using bridges Explain network segmentation using switches Explain network segmentation using routers Explain network segmentation using brouters and gateways


Repeaters: Repeaters The number of nodes on a network and the length of cable used influence the quality of communication on the network Attenuation Natural degradation of a transmitted signal over distance Repeaters work against attenuation by repeating signals that they receive on a network


Repeaters: Repeaters Figure 2-1: Repeater


Repeaters: Repeaters Note that on analog networks, devices that boost the signal are called amplifiers These devices do not have the same signal regeneration capabilities as repeaters because they must maintain the shape of the received signal Therefore, noise tends to amplified with the signal


Hubs: Hubs Generic connection device used to tie several networking cables together to create a link between different stations on a network Hubs that are plugged into electric power are called active hubs A hub that merely connects different cables on a network and provides no signal regeneration is called a passive hub and is not a repeater


Hubs: Hubs “Hub” is a generic term applied to many different network-connection devices If a hub in some way segments or subdivides the traffic on a network, it is an intelligent, or switching, hub For the purpose of the CCNS exam, the term hub—by itself—is a device that does not segment the network


Hubs: Hubs Topology Usually refers to the physical layout of network cable and devices When all stations are connected to a central hub, the topology is known as a star because of its appearance


Hubs: Hubs Figure 2-2: Star topology


Advantages and Disadvantages of Repeaters and Hubs: Advantages and Disadvantages of Repeaters and Hubs Advantages of using repeaters on your network: Repeaters can extend a network’s total distance Repeaters do not seriously impact network performance Certain repeaters can connect networks using different physical media


Advantages and Disadvantages of Repeaters and Hubs: Advantages and Disadvantages of Repeaters and Hubs Disadvantages of using repeaters on your network: Repeaters cannot connect different network architectures, such as Token Ring and Ethernet Repeaters do not reduce network traffic Repeaters do not segment the network


Advantages and Disadvantages of Repeaters and Hubs: Advantages and Disadvantages of Repeaters and Hubs Because repeaters do not segment a network, devices separated only by a repeater are susceptible to data packet collision, since they are part of the same collision domain Collision domain In Ethernet networking, a single segment on a network


Network Segmentation: Network Segmentation Segmentation Process of breaking a network into smaller broadcast or collision domains Ethernet network, which are characterized by IEEE 802.3 standard, define the use of a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) access method


Network Segmentation: Network Segmentation Backoff algorithm Mathematical calculation performed by computers after a collision occurs on a CSMA/CD network Backoff period Random time interval used after a collision has been detected on an Ethernet network


Network Segmentation: Network Segmentation Figure 2-3: Network segmentation


Bridges: Bridges Operate at the Data Link layer of the OSI model Filters traffic between network segments by examining the destination MAC address Based on this destination MAC address, the bridge either forwards or discards the frame When a client sends a broadcast frame to the entire network, the bridge will always forward the frame


Transparent Bridges: Transparent Bridges Also called learning bridges because they build a table of MAC addresses as they receive frames This means that they “learn” which addresses are on which segments Ethernet networks mainly use transparent bridges


Transparent Bridges: Transparent Bridges Figure 2-4: Bridge


Source-Routing Bridges and Translation Bridges: Source-Routing Bridges and Translation Bridges Source-routing bridges Rely on the source of the frame transmission to provide the routing information Usually employed by Token Ring networks Translation bridges Can connect networks with different architectures


Advantages and Disadvantages of Bridges: Advantages and Disadvantages of Bridges Advantages of using a bridge include: Bridges can extend a network by acting as a repeater Bridges can reduce network traffic on a segment by subdividing network communications Bridges increase the available bandwidth to individual nodes because fewer nodes share a collision domain Bridges reduce the likelihood of network collisions Some bridges connect networks using different media types and architectures


Advantages and Disadvantages of Bridges: Advantages and Disadvantages of Bridges Disadvantages of using a bridge include: Because bridges do more than repeaters by viewing the MAC addresses, the extra processing makes them slower than repeaters Bridges forward broadcast frames indiscriminately, so they do not filter broadcast traffic Bridges are more expensive than repeaters


Advantages and Disadvantages of Bridges: Advantages and Disadvantages of Bridges Because bridges forward broadcast traffic can be a major disadvantage on a network during a broadcast storm Broadcast storm Excessive broadcast messages to every host on the network, launched by multiple computers


Switches: Switches Increase network performance by reducing the number of packets transmitted to the rest of the network Like bridges, operate at the Data Link layer of the OSI model In an Ethernet network, computers are usually connected directly to a switch


Switches: Switches Virtual circuit Private connections between two points created by a switch that allows the two points to use the entire available bandwidth between those two points without contention Microsegmentation Occurs through the use of virtual circuits between switches and nodes


Switches: Switches Bandwidth Available capacity of a network Contention Condition that occurs when computers on a network must share the available capacity of the network wire with other computers


Switches: Switches Advantages of switches include: Switches increase available network bandwidth With switches, there is reduced workload on individual computers Switches increase network performance There are fewer frame collisions because switches create collision domains for each connection Switches have an unlimited number of ports and connect directly to workstations


Switches: Switches Disadvantages of switches include: Switches are significantly more expensive than bridges Network connectivity problems can be difficult to trace through a switch Broadcast traffic may be troublesome


Routers: Routers Provide filtering and network traffic control on LANs and WANs Can connect multiple segments and multiple networks Networks connected by routers are called internetworks because they create a larger network of interconnected, smaller networks


Routers: Routers When a router is introduced into a network, it creates more networks Routers create collision domains and they also create broadcast domains because a router will not pass broadcast traffic A broadcast domain is a group of network devices that will receive LAN broadcast traffic from each other


Physical versus Logical Addresses: Physical versus Logical Addresses Subnetwork Portion of the network created by manipulating a network address and breaking it down into smaller parts IP address 32-bit binary address used on TCP/IP networks Consists of a host portion and a network portion


Physical versus Logical Addresses: Physical versus Logical Addresses Notice that each port (connection) on the router has its own unique IP address Figure 2-5: Router


Advantages and Disadvantages of Routers: Advantages and Disadvantages of Routers Advantages of routers: Routers can connect different network architectures Routes can choose the best path across the network using dynamic routing techniques Routers can create collision domains by segmenting the network Routers reduce network traffic because they do not retransmit network broadcast traffic


Advantages and Disadvantages of Routers: Advantages and Disadvantages of Routers Disadvantages of routers: Routers work only with routable network protocols Routers are more expensive than bridges or repeaters Dynamic router communication causes additional network overhead Routers are slower than bridges or switches because they must analyze a data transmission from the Physical through the Network layer


Brouters: Brouters Device that functions as: A bridge for nonroutable protocols A router for routable protocols Operates at both the Data Link and Network layers


Gateways: Gateways Gateways Combination of hardware and software Translate between different protocols on a network Latency Delay on a network caused by a variety of factors


Chapter Summary: Chapter Summary Network administrators use devices to control and extend usable size of a network Repeaters work against attenuation by cleaning and repeating signals that they receive on a network A hub ties several networking cables together to create a link between different stations on a network


Chapter Summary: Chapter Summary Bridges and switches are devices commonly used to segment networks Routers provide filtering and network-traffic control on LANs and WANs A brouter is a hybrid device that functions both as bridge for nonroutable protocol and a router for routable protocols Gateways are usually a combination of hardware and software and are used to translate between different protocols