Network Devices Hubs, Switches, Routers

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Network Devices A LAN can refers to a Broadcast Domain / a Subnet LAN traffic congestion is caused by Too many hosts in a broadcast domain Excessive broadcasts Multicasting Low / insufficient bandwidth To solve this we can segment the network

Hubs and Repeaters Layer 1 of the OSI The physical layer (moving bits on physical media) Hubs repeat signals received on each port by broadcasting to all the other connected ports. Repeaters used to connect two or more Ethernet segments of any media type, and to provide signal amplification for a segment to be extended. Ethernet is subject to the "5-4-3" rule regarding repeater placement, meaning we can only have five segments connected using four repeaters with only three segments capable of accommodating hosts.

Bridges and Switches Layer 2 of the OSI The data link layer (based on the Ethernet packet / mac address) Bridges used to connect different networks types cannot filter out broadcast traffic

Bridges segment collision domains. Only 2 networks can be linked with a bridge. Bridges are layer 2 devices (Data Link layer) which are usually used to segment a LAN into two segments. Bridges examine frames, keeping local traffic local, and forwarding any non-local traffic. Each port on a bridge is a separate collision domain i.e. ports A, B, C here. Important points to remember about bridges: each segment connected to a bridge is in a separate collision domain; all segments on a bridge are in the same broadcast domain; and bridges forward all broadcast messages.

A Collision Domain A collision domain is any area where a collision can theoretically take place, so only one device can transmit at a time in a collision domain. Switches breakup collision domains, each port on a switch represents a collision domain. Most cannot filter out broadcast traffic. 3 main switching methods are 1. Cut Through - looks at the first 6 bytes of the destination MAC address only 2. Fragment free cut through - looks at the first 64 bytes only 3. Store and forward - looks at the entire frame

Routers Layer 3 of the OSI The network layer (logical ip addressing) Routers do not forward broadcast traffic they perform packet switching / filtering by determining the most efficient path for a packet to take sending packets around failed segments. Routers also connect remote networks providing internetwork communication. Routers break-up a broadcast domain and collision domains as they dont forward broadcasts by default.

Question

Refer to the exhibit. How many broadcast domains are there in the topology shown, assuming that VLANs are not configured on the switches? A. one B. two C. three D. four E. six F. eight Answer B Two Note the trick question, says broadcast domains therefore answer is 2 not 8

Gateways enable communications between different protocols, data types and environments. Gateways operate at all layers of the OSI model without making any forwarding decisions. A router that provides the connection between a lan and the internet is the default gateway. In this situation the layer 3 router operates at layer 4 the

transport layer (tcp/udp) as it forwards protocols directly to specific network devices ie web/email server.

Question The Sales and Production networks are separated by a router, which of the following statements most accurately describes the characteristics of the networks broadcast and collision domains.

A. There are two broadcast domains in the network B. There are four broadcast domains inn the network C. There are six broadcast domains in the network D. There are four collision domains in the network E. There are five collision domains in the network F. There are seven collision domains in the network

Answer A, F Explanation We have a hub in the sales department and a switch in the production department. Therefore we have two broadcast domains one for each network separated by a router. For collision domains we have 5 pcs and one port for e1 so we have 6 collision domains on the switch side of things plus one more for the hub side total = 7.

Exam QuestionsQuestion At Layer 2 of the OSI model, which component connects a host to the network media? A. Hub B. Switch C. Bridge D. NIC E. Transceiver Answer D Explanation The data link layer is layer 2 of the OSI model. The data link layer involves frames and uses the burned in MAC addresses that NIC cards and router interfaces have. Incorrect Answers A. A hub operates at the physical layer, layer 1. B. Switches operate the Data Link layer, layer 2, of the OSI model. However, they are not used to connect hosts to the network media. C. Bridges operate the Data Link layer, layer 2, of the OSI model. However, they are used to connect network segments, not to connect hosts to the network media. E. A transceiver works at the physical layer, layer 1.

Question Study the network topology exhibit carefully, in particular the two switches SW1, SW2, and the router RT3. Which statements are true in this scenario? (Select two)

A. The hosts on the 192.168.1.0 network form one collision domain and the hosts on the 192.168.2.0 network form a second collision domain. B. Each host is in a separate collision domain. C. All the devices in both networks will receive a broadcast to 255.255.255.255 sent by host A. D. Only the devices in network 192.168.1.0 will receive a broadcast to 255.255.255.255 sent by host A. E. All the devices on both networks are members of the same collision domain. Answer B & D Each host is in a separate collision domain.

Only the devices in network 192.168.1.0 will receive a broadcast to 255.255.255.255 sent by host A. Question Which of the following describe router functions? (Choose three) A. Packet switching B. Collision prevention on a LAN segment C. Packet filtering D. Broadcast domain enlargement E. Broadcast forwarding F. Internetwork communication Answer A, C, F Explanation A. Router works in Layer 3 in OSI Model. Packet switching is function of OSI Layer 3. C. In Packet switching process, packet will be filtered at a particular physical Interface during packet switching. F. In OSI Model each layer dependent on the layer below and above layer for Internetwork communication. Here Router works with Data Link layer and Transport layer. Incorrect answers A. Collision will occur on physical layer. It is not related to Router D, E. Broadcast activity is not the function of Router. Router will not transmit Broadcast information out to another router.

Question Which of the following contribute to congestion on an Ethernet network. (Choose two) A. Use of full duplex mode. B. Creation of new collision domain. C. Creation of new broadcast domain. D. Addition of hub to the network. E. Use of switches in the network. F. Amount of ARP or IPX SAP traffic. Answer D, F The Addition of hub to the network and the amount of ARP or IPX SAP traffic. Explanation D. Hub works on Half duplex mode. If more devices connect to a hub and sending simultaneously collision will occur .It contributes to congestion. F. ARP also creates congestion in the network Incorrect answers A. Full Duplex will not generate congestion in the network. B. Creation of new collision domain means connecting a switch instead of Hub will not contribute congestion. Switch isolates collision domain. C. Creation of VLANs in a switch isolate broadcast domain. Each Vlan is separate broadcast domain. It will not generate congestion in network.

Question What feature of a networks switch allows an administrative to create separate broadcast domains? A. Store-and-forward switching B. Microsegmentation C. Transparent bridging D. Fragment-free switching E. Virtual LANs F. Cut-through switching Answer E Explanation Creation of VLAN in a switch provide separate Broadcast domain. If VLAN is not there all ports as members of one Broadcast domain. Incorrect Answers A. This is one of the Switching method in a switch. It will not play any role for creating separate broadcast domains B. Not related to the question C. Transparent bridging is called Transparent because the endpoints devices do not need to know that the bridges exists. It will not play any role for creating separate broadcast domain

Question Which statement describes the rule of split horizon? A. Only routers can split boundaries (horizons) between concentric networks. B. All distance vector protocols require fall back routers that may cause momentary loops as the topology changes. C. Networks can only remain fully converged if all information about routers is sent out all active interfaces. D. Information about a route should not be sent back in the direction from which the original update came. E. Each AS must keep routing tables converged to prevent dead routes from being advertised across the AS boundary. Answer D Information about a route should not be sent back in the direction from which the original update came. Explanation Split horizon includes two related concepts that affect what routes are included in a routing update An update does not include the subnet of the interface out which the update is sent All routes with outgoing interface of interface x are not included in updates sent out that same interface x. Incorrect Answers A. There is no such requirement B. Distance vector protocols updates routing table at regular intervals instead of Topology changes C. This is not a feature of split horizon E. This is not a related feature for split horizon

Question Your trainee, asks you about basic characteristics of switches and hubs for network connectivity. What should you tell him? A. Switches take less time to process frames than hubs take. B. Switches do not forward broadcasts. C. Hubs can filter frames. D. Using hubs can increase the amount of bandwidth available to hosts. E. Switches increase the number of collision domains in the network. Answer E Expla