CCNA 3 Study Guide Answers-All

CED255 INTERNETWORKING III, Ver. 3.0MODULE 1 STUDY GUIDE

1. VLSM stands for:

Variable Length Subnet Masking

2. The purpose VLSM was designed was to:

Conserve IP addresses when using IPv4, maximizing the number of useable IP addresses available in a network.

3. Dynamic routing protocols that support VLSM include:

OSPF RIP v. 2 EIGRP IS-IS

4. VLSM is sometimes referred to as __________________________.

Subnetting a subnet

5. What is an “autonomous system”?

it’s a network used in one enterprise

6. What is meant by “route aggregation”?

It’s the same thing as route summarization; it’s a way to summarize more than 1 route with one route entry in a router’s routing table.

7. How can you take advantage of route aggregation using VLSM?

Make sure your VLSM routes are not distant from each other. This way routes can be aggregated into one route in the routing table.

8. Is RIP v. 1 a classful or classless protocol? RIP v. 2? What does this mean?

RIP v. 1 is classful; RIP v. 2 is classless. It means that RIP v. 1 must stay within the “normal” IP class system (A, B, C); classless means RIP v. 2 can use VLSM.

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9. Because it’s a new protocol, can RIP v. 2 hop more than 16 times?

No. It still has many of the same characteristics of RIP v. 1, including hop count max of 16.

10.What is the configuration command to start RIP v. 2 running?

Router(config)#router ripRouter(config-router)#version 2Router (config-router)#network [attached network(s)]orRouter(config)#router rip ver 2

11.What show commands can you use to ensure that RIP v. 2 has started running?

show ip routeshow ip protocols

12.What is the command to flush (clear) the routing table to force an update?

clear ip route *

13.What will you see if you use the debug ip rip command?

You’ll see all the RIP updates as they are sent and received by the router.

14.How do you turn off the debugging function?

Add “no” to the same command you used to turn it on, or you can use the “no debug all” to turn off all debugging.

15.What are the three (3) ways that routers learn about routes (networks)? Briefly explain each one.

Static routing - additions to the routing table put in by the network administrator

Dynamic routing – additions to the routing table are added automatically as routers update themselves using protocols

Default routes - default routes added to the routing table by the network administrator that indicates the path to take when there is no known route to the destination

16.What are the two commands that can be used to enter a default route?

ip route [network no.] [subnet mask] [next hop IP address]ip default-network [network to use as default]


17. If you want to use the ip route command to specify a default network, how would you enter it?

ip route 0.0.0.0 0.0.0.0 [next hop IP address]



1. What are the two main ways of classifying dynamic IGP routing protocols?

Distance-vectorLink-state

2. Which ones are also known as “shortest path first” protocols? Why?

Link-state, because that’s exactly what they do: they look for the shortest path to the destination (regardless of whether or not this is the BEST path).

3. Fill in the following table:

Type Protocol(s) Advantages DisadvantagesDistance-Vector RIP v. 1

RIP v. 2IGRP

Easy to configureUpdates regularly

Takes up significant bandwidthSlow to convergeSubject to routing loopsRIP only has 1 metricOnly RIP v. 2 can use VLSM

Link-State OSPF,IS-IS

Only sends out updates as neededDoesn’t use much bandwidth to maintain tablesFast to convergeNot subject to routing loopsKnows complete topology of network so knows all routesUses cost metrics instead of distance metricsCan use VLSM and CIDR

Difficult to configure correctlyRequires more memory and more powerful CPUs in routersTakes a lot of bandwidth when first started

4. What are “hello” packets used for?

Link state protocols use them to make sure a link is still active. They’re very small packets.


5. What are the five things that link state protocols use to maintain their tables:

Link-state advertisements (LSAs) A topological database The shortest path first (SPF) algorithm The resulting SPF tree A routing table of paths and ports to each network to determine the best

paths for packets

6. What is meant by a “link” when talking about link state protocols?

A link is an interface on a router.

7. How does a link state protocol build its topological database? What kind of information is in it?

It’s a database of the entire topology of the network and includes each link and how to reach it. It’s built by using the LSAs that have been received by the router.

8. What are the three types of networks recognized by OSPF?

Broadcast multi-access, such as Ethernet Nonbroadcast multi-access (NBMA), such as frame relay Point-to-point networks

9. What is the DR and the BDR in an OSPF network? What do they do?

DR – Designated Router acts as the “brains” of the network. This router makes sure that all the LSAs are sent to all the other routers in the Area.

BDR – Backup Designated Router acts as the “second in command” of the network. If the DR goes down, the BDR takes over as DR. However, until the DR goes down, the BDR does not send out LSAs to any other routers in the Area.

10. What is the multicast address used by the DR to send out LSAs to all other OSPF routers? For LSAs just to other designated (and backup) routers?

224.0.0.5224.0.0.6


11. What is a hello packet used for and what is the multicast address used for it? Why this address?

A hello packet is the way OSPF routers make sure that a link is still active. 224.0.0.5 is the address used so that all links are checked, not just DRs and BDRs.

12. What is the default hello interval?

10 seconds

13. What is the main area of an OSPF network designated?

Area 0 (zero)

14. What is the command used to start OSPF routing on a router?

Router(config)#router ospf [process ID]

15. What is the processor ID?

It’s an identifier for the OSPF routing process on the router

16. What is the command used to identify networks on an OSPF router?

Router(config-router)#network [network no.] [wildcard-mask] area [area-id]

17. What does an OSPF router use for its router ID? How can you force a different ID?

It uses the highest active IP address on any of the interfaces (where OSPF is running). If you want to change the ID, set a Loopback interface with a higher IP address so it will be forced to be the ID.

18. What is a Loopback?

It is a logical (virtual) interface; not a physical (real) one

19. What is the command used to set a Loopback?

Router(config)int Loopback[No.]Router(config-if) ip addr [IP number] [subnet mask]

20. What is the recommended subnet mask to use on a Loopback interface?

255.255.255.255


21. What is a “priority” number used for? How can you change it?

If there is more than 1 router in the Area (broadcast multi-access), then there must be a DR and maybe a BDR for the Area. The priority number is used to determine which routers will be the DR and the BDR.You can change it with the following command:

Router(config-if)#ip ospf [priority number]

22. Why must you set the bandwidth on an interface running OSPF? What is the default bandwidth? How can you change it?

Cost (the default metric of OSPF) uses bandwidth to determine the best route. The default is 1.544 Mbps. You can change it with the command:

Router(config)#interface [type] [number]Router(config-if)#bandwidth [Kbps]

23. How can OSPF routers authenticate each other?

They exchange passwords that only other OSPF routers will know. Use the commands below to set authentication:

Router(config-if)#ip ospf authentication-key [password]Router(config-router)#area [area-number] authentication

24. What is the difference between default authentication and a message-digest authentication procedure? What is the command to do the latter?

The default authentication sends the password in plain text; message-digest encrypts the password that’s sent.

Router(config-if)#ip ospf authentication message-digest-key [key-id] md5 [encryption-type key]

Router(config-router)#area [area-id] authentication message-digest

25. What is the relationship between the “hello” packet interval and the “dead” interval? What is meant by the “dead” interval?

The dead interval is 4 times the hello interval (e.g., hello is 10 seconds, so dead is 40 seconds).The dead interval is the time used to determine that a link is down, or dead. In other words, if a hello isn’t received from a link for the space of 4 times the normal hello interval, it’s considered dead.


26. What would happen if routers in the OSPF network have different hello intervals configured?

They wouldn’t be able to “talk” to each other, so would be considered inactive. Hello intervals must be the same on all the routers in the network.

27. What is the best way to define a default route on an OSPF router?

Use the “quad zero” command:Router(config)#ip route 0.0.0.0 0.0.0.0 [interface or IP address of next hop]

28. How can you make sure that this information is propagated to other routers in the area?

Router(config-router)#default-information originate

29. List some of the show commands you can use to make sure that OSPF is functioning correctly.

Show ip routeShow ip protocolShow ip ospf interfaceShow ip ospfShow ip ospf neighbor [detail] (shows neighbor database)Show ip ospf database (shows topological database)



1. What is the difference between IGRP and EIGRP?

EIGRP supports VLSM and CIDR, it has faster convergence times, it’s more scalable, and handles routing loops better than IGRP does.

2. Why is EIGRP referred to as a hybrid protocol?

Because it primarily is a distance vector protocol, but also has some characteristics of a link state protocol, such as sending hello packets, sending only partial updates (instead of entire table exchanges), and using neighbor discovery. However, it’s easier to configure than OSPF.

3. Can IGRP and EIGRP routers “talk” to each other? Why or why not?

Yes, they can talk because EIGRP is simply an enhancement of IGRP; they’re still basically the same protocol.

4. List the three tables that EIGRP maintains and briefly describe each one.

Topology – lists all routing tables in the AS; all learned routes are in this tableNeighbor – lists adjacent routers, their addresses and interfacesRouting – lists best route to each destination network

5. List the five pieces of information found in the topology table and briefly describe each one.

Feasible distance – The feasible distance (FD) is the lowest calculated metric to each destination.

Route source – The source of the route is the identification number of the router that originally advertised that route. This field is populated only for routes learned externally from the EIGRP network. Route tagging can be particularly useful with policy-based routing.

Reported distance – The reported distance (RD) of the path is the distance reported by an adjacent neighbor to a specific destination.

Interface information – The interface though which the destination is reachable

Route status – Routes are identified as being either passive (P), which means that the route is stable and ready for use, or active (A), which means that the route is in the process of being recomputed by DUAL.


6. What is DUAL?

The EIGRP distance vector algorithm is called the Diffusing Update Algorithm (DUAL). DUAL tracks all the routes advertised by neighbors. Composite metrics of each route are used to compare them. DUAL also guarantees that each path is loop free. DUAL inserts lowest cost paths into the routing table. These primary routes are known as successor routes. A copy of the successor routes is also placed in the topology table.

7. What is the difference between a “feasible successor” route and a :successor” router?

The successor route is the route in the routing table; in other words, the route considered the best to the destination. The feasible successor is the back-up route, or the next-best route.

8. What makes EIGRP able to support IP, IPX, and AppleTalk?

It uses PDMs (protocol dependent modules). Also, for AppleTalk, it can actually act as the primarily protocol and AppleTalk doesn’t even have to be running.

9. What is RTP? What does it do?

Reliable Transport Protocol is a transport-layer protocol that can guarantee ordered delivery of EIGRP packets to all neighbors. This means EIGRP does not rely on TCP/IP to exchange routing information the way that RIP, IGRP, and OSPF do. To stay independent of IP, EIGRP uses RTP as its own proprietary transport-layer protocol to guarantee delivery of routing information.

What are the five EIGRP packet types? Briefly describe each one.

Hello - discover, verify, and rediscover neighbor routers Acknowledgement - to indicate receipt of any EIGRP packet during a

reliable exchange Update - used when a router discovers a new neighbor. An EIGRP router

sends unicast update packets to that new neighbor, so that it can add to its topology table

Query - uses query packets whenever it needs specific information from one or all of its neighbors

Reply - used to respond to a query


What are the commands used to start EIGRP running on a router?

router(config)# router eigrp [autonomous-system-number]router(config-router)# network [network number]router(config)#int [type] [number]router(config-if)# bandwidth [kilobits]router(config-if)# eigrp log-neighbor-changes

If you do not want to summarize routes, what is the command to turn it off? Why might you not want to summarize (aggregate) routes?

router(config-router)#no auto-summary

If you have discontiguous subnets (subnets not right beside each other in the numbering scheme), route summarization probably won’t work right.

List some of the show commands you can use to verify that EIGRP is running correctly.

show ip routeshow ip eigrpshow ip protocolshow ip eigrp neighbor [details]show ip eigrp interfaceshow ip eigrp topologyshow ip eigrp traffic

Which table built by EIGRP is considered the most important? List the fields of information contained in this table and briefly describe each one.

The neighbor table. Neighbor address –network layer address of the neighbor router Hold time –interval to wait without receiving anything from a neighbor

before considering the link unavailable. Originally, the expected packet was a hello packet, but in current Cisco IOS software releases, any EIGRP packets received after the first hello will reset the timer.

Smooth Round-Trip Timer (SRTT) –average time that it takes to send and receive packets from a neighbor; used to determine the retransmit interval (RTO).

Queue count (Q Cnt) –number of packets waiting in a queue to be sent. Sequence Number (Seq No) –number of the last packet received from that

neighbor; used to acknowledge a transmission of a neighbor and to identify packets that are out of sequence.


What is the most common problem that keeps RIP tables from updating?

The use of VLSM and RIP v. 1, which doesn’t support it.

What is the most common type of networking problem?

Layer 1 issues (cabling is the most prevalent)



1. Why is Ethernet described as a collision-prone network?

Because of the nature of Ethernet. It is a broadcast technology, which means that it is a shared technology where every packet is broadcast to every device on the segment. It is also non-deterministic, which means any device can transmit at any time. This makes it prone to collisions.

2. What networking device can help cut down or even eliminate collisions on an Ethernet network? Why?

A switch because every port on a switch acts like a mini-bridge, making it a separate collision domain. Only those devices that are on that port of the switch will be in the same collision domain. If each port goes to a separate workstation or printer, then you basically will eliminate all collisions.

3. What does the term “microsegmentation” mean?

It is segmenting a network into point-to-point collision domains using switches, which gives maximum usage of bandwidth.

4. Fill in the following table:

Item LayerRouter 3Switch 2Bridge 2Passive hub 1Active hub 1Transceiver 1IP address 3MAC address 2Packets 3Frames 2Data segments 4Repeater 1

5. What is the most common LAN architecture used today?

Ethernet


6. Explain CSMA/CD. What does it stand for and how does it apply to Ethernet networks?

Carrier Sense Multiple Access/Collision Detect: this is the technology that Ethernet is built on. Since Ethernet devices can transmit at will, CSMA/CD has been built into them so that they will listen to the media first to see if there is any traffic on it before transmitting. This is how Ethernet tries to avoid collisions. However, if a collision occurs, it is detected very quickly and all devices are told not to transmit for the back-off time to avoid more collisions.

7. What is meant by “half-duplex” technology?

A device can either transmit or receive, but not both at the same time.

8. What does the term “latency” mean?

It is the delay the time a frame or a packet takes to travel from the source station to the final destination. Latecncy is is inherent in different types of networks and networking devices.

9. What are the three sources of latency on an Ethernet network?

First, there is the time it takes the source NIC to place voltage pulses on the wire and the time it takes the receiving NIC to interpret these pulses. This is sometimes called NIC delay, typically around 1 microsecond for a 10BASE-T NIC.

Second, there is the actual propagation delay as the signal takes time to actually travel along the cable. Typically, this is about .556 microseconds per 100 m for Cat 5 UTP. Longer cable and slower nominal velocity of propagation (NVP) results in more propagation delay.

Third, latency is added according to which networking devices, whether they are Layer 1, Layer 2, or Layer 3, are added to the path between the two communicating computers. The actual transmission time, the duration of time to actually send the bits, must also be included in understanding timing on networks.

10.What is meant by “bit time” in Ethernet networks?

It is defined as the basic unit of time in which one bit can be sent.


11.What is meant by the term “attenuation” when talking about data networks? What causes it?

Attenuation means that the signal weakens as it travels through the network. The resistance in the cable or medium through which the signal travels causes the loss of signal strength.

12.What is meant by “full duplex” technology? Which Ethernet connections can take advantage of it? What does it take in order to create a full duplex network?

It means that a device can both send and receive at the same time. Ethernet 10BASE-T, 100BASE-TX, or 1000BASE-Fx can use full duplex.A dedicated port on a switch that can support full duplex is required for each node

13.How many wires does it take to make a full-duplex cable? How much of the bandwidth is available on a full-duplex network?

it takes two pairs for full duplex. 100% of the bandwidth in both directions is available on full duplex because there is one pair of wires for sending and another for receiving data.

14. Is there an advantage of segmenting a network using switches instead of routers? Disadvantages?

Yes, switches introduce less latency onto the network. They only add 10-30% latency; routers add 20-30% latency. However, switches only can segment at Layer 2 to create separate collision domains; routers can segment at Layer 3 (networks) and can subnet in separate networks.

15.What is the main reason for LAN segmentation?

It improves the performance of shared media (cuts down on collision domain size)

16.Are there more or fewer collision domains in a microsegmented LAN? Why?

There are more collision domains in a microsegmented LAN because switches break a LAN down into smaller “LANs” by segmenting them. This makes smaller—but more—collision domains.

17.What are the two main functions of switching devices?

Switching data frames Maintaining switching operations


18.What type of circuits does a switched LAN create? What is one advantage of using switches on a LAN?

virtual circuits. Switches create many small collision domains so collisions are almost totally avoided, thus speeding up transmission.

19.What is the difference between a symmetric and asymmetric switch?

symmetric switches switch between like media (same bandwidth); asymmetric switches switch between unlike media (different bandwidths).

20.Where does a switch store destination and transmission data? Describe the difference between the two main types.

In memory buffers in queues. In port-based memory buffering, packets are stored in queues that are linked to specific incoming ports. Shared memory buffering deposits all packets into a common memory buffer which all the ports on the switch share.

21.What are the two switching methods? What are the main differences between the two?

store-and-forward switching, cut-through switching. The main difference is that store-and-forward waits until the entire frame has been received before it sends it on its way; cut-through switching reads the destination MAC address on the incoming frame and immediately begins sending it on through (before the entire frame is received).

22.What are the two sub-types of cut-through switching?

Fast Forward – only reads the destination MAC address and immediately starts forwarding the frameFragment Free – makes sure there area at least 64 bytes of data to send before forwarding the frame (anything less than 64 bytes is a fragment)

23.What are the two main reasons to use of Ethernet switches in a network?

Isolate traffic among segments Achieve greater amount of bandwidth per user by creating smaller collision

domains

24.What are the three main frame transmission modes used by Ethernet switches?

Cut Through Store and Forward Fragment Free


25.What is the fourth mode? What is different about it?

Adaptive cut-through – With this mode, the switch uses cut-through until it detects a given number of errors. Once the error threshold is reached, the switch changes to store and forward mode. This method is sometimes referred to as Error sensing

26.What does a bridge use to forward data packets? How does it learn this information?

They use MAC address to forward/not forward data packets to another segment. They learn new MAC addresses from the source address in the header of a packet and add this info to a MAC table they build.

27.How does a switch learn MAC addresses? What happens when a switch adds a new MAC address to its table?

Switches learn MAC addresses from incoming packets. They add these addresses to their MAC tables so they can remember which segment hosts which nodes. Each new address is time stamped so the switch can determine which address are still good and which are old.

28.What is Content-Addressable memory (CAM) used for in switch applications?

To take out and process the address information from incoming data packets

To compare the destination address with a table of addresses stored within it

29.What do switches/bridges use to filter frames?

They can filter frames based on any Layer 2 fields

30.Can switches filter broadcast or multicast frames? Why or why not?

Most Ethernet switches can filter broadcast and multicast frames, because today, they are able to filter according to the network-layer protocol.


31.What are the three ways of communicating on a data network? Briefly describe each one.

Unicast – one transmitter tries to reach one receiver Multicast –one transmitter tries to reach only a subset, or group, of the

entire segment broadcasting Broadcast – one transmitter tries to reach all the receivers in the network.

The server station sends out one message and everyone on that segment receives the message.

32.What is the MAC address for a broadcast message?

FF:FF:FF:FF:FF:FF



33.What are the four components that make up a successful network design? Briefly describe each one.

Functionality – The network must work. The network must allow users to meet their job requirements. The network must provide user-to-user and user-to-application connectivity with reasonable speed and reliability.

Scalability – The network must be able to grow. The initial design should grow without any major changes to the overall design.

Adaptability – The network must be designed with a vision toward future technologies. The network should include no element that would limit implementation of new technologies as they become available.

Manageability – The network should be designed to facilitate network monitoring and management to ensure ongoing stability of operation.

34.To maximize bandwidth and availability of resources, what should you consider when designing a LAN?

The function and placement of servers Collision detection issues Segmentation issues Broadcast domain issues

35.What are the two main groups of servers? Give some examples of each would do and would be located.

Enterprise – DNS, e-mail, DHCP; located in Distribution Facilities (either MDF or IDFs)Application – applications used by workers (Word, Excel, Accounting, etc.); located close to the users

36.What are the steps you should follow in order to create a successful network design?

Gather requirements and expectations Analyze requirements and gathered data Design the Layer 1, 2, and 3 LAN structure, or topology Document the logical and physical network implementation

37.What is meant by “availability”? Give some examples.

Availability measures the usefulness of the network; it includes throughput, response time, and access to resources


38.What layers of the OSI model are you primarily working with when you’re designing a network? What is involved at each layer?

Layer 1 – what type of media will be used in the network Layer 2 – how will the network be segmented at this layer; where will

switches be placed in the network? Layer 3 – how will the network be subnetted (or will it be) and how

should those subnets be allowed to communicate; where should routers be injected into the network?

39.What are MDFs and IDFs? What would you find in them?

They are wiring rooms (telecommunication rooms/distribution facilities). This is where all the networking devices (routers, switches, hubs, patch panels, telephone connections, etc.) should be located. This is the end-point of your horizontal cabling.

40.What is the difference between horizontal cabling and vertical cabling?

Horizontal cabling runs from the workareas to the DF; backbone cabling is the main cable running from floor-to-floor carrying the majority of the data to the major networking devices (switches and routers).

41.List some of the documents you should create as you design and build your network.

The exact locations of the MDF and IDF wiring closets The type and quantity of cabling used to interconnect the IDFs with the

MDF, along with how many spare cables are available for increasing the bandwidth between the wiring closets.

Detailed documentation of all cable runs, the identification numbers, and which port on the HCC or VCC the run is terminated on

List of devices and their locations The IP addressing should be documented by site and by network within the

site. A standard convention should be set for addressing important hosts on the network. This addressing scheme should be kept consistent throughout the entire network. Addressing maps provide a snapshot of the network.

Physical maps of the network (helps to troubleshoot the network)


42.What is the hierarchical design model? Why would you want to use it? What are the three layers of this design model? Briefly describe each one.

It is a design model that breaks a network into three distinct layers. It is a good idea to use a hierarchical design because this will make it easier to make changes to the network as the organization grows. The three layers are:

The Access Layer – provides users in workgroups access to the network The Distribution Layer – provides policy based connectivity The Core layer – provides optimal transport between sites. The core layer

is often referred to as the backbone

43.What layer of the OSI model do access switches run at? What are they designed to do? List a few of the Cisco models.

They run at Layer 2 (although they have some Layer 3 characteristics) and their main purpose is to allow end users into the network. Some of the Cisco models are 1900 series, 2950 series, 4000 series, and 5000 series.

44.What layer of the OSI model do distribution switches run at? What are they designed to do? List a few of the Cisco models.

Switches in this layer operate at Layer 2 and Layer 3 and they aggregate the wiring closet connections, define broadcast/multicast domains, allow Virtual LAN (VLAN) routing, create any media transitions that need to occur, and add security to the network. Some of the models are 2926G, 5000 series, and 6000 series.

45.What layer of the OSI model do core switches run at? What are they designed to do? List a few of the Cisco models.

Core switches are designed to use Layer 2 or Layer 3 switching and switch packets as fast as possible and do not perform any packet manipulation, such as access list filtering, which would slow down the network. An example of a core switch is an ATM switch. Some of the models include Catalyst 6500 series, Catalyst 8500 series, IGX 8400 series, and Lightstream 1010.



1. What types of ports/interfaces does a configurable switch normally have?

Ports (10/100/1000Mpbs) to connect devices; console port; higher speed ports for backbone cables.

2. What do the LEDs on the switch do?

Alert you as to whether or not ports are working correctly Whether power is being received into the switch from the power

connection Whether a remote power source is being used or not Current mode being used by switch

3. What is a POST? When is it performed?

Power On Self-Test. It is performed by the device upon power-up.

4. What kind of cable is required to access the console port on a switch or router? Which port do you use? How do you know what’s going on on the device?

Roll over cable into the console port. You normally use a HyperTerminal or Telnet session from a PC to see what is happening on the device.

5. Where is the power switch on a Cisco switch?

There is none. You simply plug in the switch to the power source.

6. What does CLI stand for? How does it differ on a Cisco switch from a router?

Command line interface. It doesn’t differ very much—they both use the Cisco IOS; the only thing that’s a little different is the particular command set available on each.

7. List (in order) the EXEC modes on the Cisco switch.

User EXEC Enable/privileged EXEC Global configuration EXEC Particular configuration EXEC (e.g., interface, line, etc.)


8. What are the steps you should follow in order to completely configure a switch that may already have a configuration on it?

Remove any existing VLAN information by deleting the VLAN database file VLAN.dat from the flash directory

Erase the back up configuration file startup-config Reload the switch

9. List some of the things you should configure on a switch to ensure it is secure, yet easy to access for those authorized to do so.

switch should be given a hostname passwords should be set on the console and vty lines IP addresses and a default gateway should be set In a switch-based network, all internetworking devices should be in VLAN

1, the management VLAN

10. Identify what the following commands will do on the switch:

Command PurposeSwitch#show mac-address-table Displays the MAC tableSwitch#clear mac-address-table Clears all entries out of the MAC table

and forces it to rebuild itselfSwitch(config)#mac-address-table static [mac address of host] interface [type][number] vlan [number or name]

To set a static MAC address in the MAC table

Switch#show port security Display switch security on ports



1. What is meant by “redundant technologies” when talking about networks? Why or why not is this a good thing?

Redundancy means to be in excess or exceeding what is usual and natural. Fault tolerance is achieved by redundancy. Normally, this is a good thing for a network.

2. What is a drawback of having a redundant switched topology?

It may cause broadcast storms, multiple frame copies, and MAC address table instability problems. It is possible for switches to learn the wrong information. A switch can learn that a MAC address is on a port when it is not really on that port.

3. What is the answer to this problem?

To create a logical loop-free topology, which is called a tree. The Spanning Tree Algorithm is used to span all the trees, thus creating a loop-free logical topology.

4. What is the IEEE standard for Spanning Tree? What does it specify

802.1d; It specifies that the STP (spanning tree protocol) use the Spanning Tree Algorithm (STA) to construct a loop free shortest path network. Shortest path is based on cumulative link costs. Link costs are based on the speed of the link.

5. What are BPDUs? What information contained in these BPDUs allow the switch to create the loop-free topology?

The message that a switch sends allowing the formation of a loop free logical topology is called a Bridge Protocol Data Unit (BPDU).

Select a single switch that will act as the root of the spanning tree Calculate the shortest path from itself to the root switch For each LAN segment, designate one of the switches as the closest one to

the root. This bridge is called the “designated switch.” The designated switch handles all communication from that LAN towards the root bridge.

Each non-root switch chooses one of its ports as its root port. This is the interface that gives the best path to the root switch.

Select ports that are part of the spanning tree, the designated ports. Non-designated ports are blocked.


6. What are the four elements that must exist on every switch in a spanned, switched network?

One root bridge per network One root port per non root bridge One designated port per segment Non designated ports are unused

7. Which switch will become the root bridge in a network running STP?

The switch with the smallest BID (bridge ID) number.

8. How often are BPDUs sent out by default?

Every 2 seconds

9. What are the five STP states? Briefly describe each one.

blocking state - ports can only receive BPDUs; data frames are discarded and no addresses can be learned

listening state - switches determine if there are any other paths to the root bridge (called the forward delay)

learning state - user data is not forwarded, but MAC addresses are learned from any traffic that is seen (also called the forward delay)

forwarding state - user data is forwarded and MAC addresses continue to be learned; BPDUs are still processed

disabled state - occurs when an administrator shuts down the port or the port fails

10. What is the definition of a converged switched internetwork?

When all the switch and bridge ports are in either the forwarding or blocked state

11. What does the 802.1w standard define?

Rapid Spanning Tree Protocol



1. What is the definition of a VLAN?

A VLAN is a group of network services that is not restricted to a physical segment or switch. VLANs logically segment switched networks based on an organization's functions, project teams, or applications as opposed to a physical or geographical basis.

2. Is a VLAN able to contain broadcasts?

Yes, a VLAN may be thought of as a broadcast domain that exists within a defined set of switches

3. How does a switch that has multiple VLANs on it switch frames that come into it?

The switch maintains a separate bridging table for each VLAN, so if a frame comes in on a port in VLAN 1 the switch searches the bridging table for VLAN 1

When the frame is received, the switch adds the source address to the bridging table if it is currently unknown.

The destination is checked so a forwarding decision can be made. For learning and forwarding the search is made against the address table

for that VLAN only.

4. What are the three main ways that VLANs are organized?

Port-centric, statically, dynamically

5. List some of the advantages of VLANning a network.

Easily move workstations on the LAN. Easily add workstations to the LAN. Easily change the LAN configuration. Easily control network traffic. Improve security.

6. What are the three basic models for determining and controlling how a packet gets assigned to a VLAN?

Port-based VLANS. MAC address based VLANs. Protocol based VLANs


7. What happens to the frame header when using any of the above models?

A VLAN ID is inserted into it before the frame is transmitted onto the link between the VLANs.

8. What is the most used frame tagging option used in switching? What is special about this?

Inter-Switch Link (ISL); it’s a Cisco-proprietary protocol that maintains VLAN information as traffic flows between switches and routers.

9. How can you make an ATM network look like an Ethernet network?

LAN emulation (LANE) is a way to make an Asynchronous Transfer Mode (ATM) network simulate an Ethernet network

10.What type of address must be assigned to each VLAN?

A unique Layer 3 network address

11.What characteristics should an end-to-end VLAN network comprises?

Users are grouped into VLANs independent of physical location, but dependent on group or job function.

All users in a VLAN should have the same 80/20 traffic flow patterns. As a user moves around the campus, VLAN membership for that user

should not change. Each VLAN has a common set of security requirements for all members.

12.What does standard 802.1q pertain to?

Fast Ethernet Inter-Switch Link (ISL), which is used to carry multiple VLAN information between the wiring closets and the distribution layer switches.

13.What is meant by a static VLAN? What are some advantages/disadvantages of this method?

Ports on a switch are manually assigned to a VLAN by using a VLAN management application or by working directly within the switch. Advantage is that they’re very secure and easy and straightforward to configure; disadvantage is that they must be configured and updated manually by an administrator.


14.What is meant by a dynamic VLAN? What are some advantages/disadvantages of this method?

Do not rely on ports assigned to a specific VLAN. Instead, VLAN assignment is based on MAC addressing, logical addressing, or protocol type. Advantage is that the switch takes care of VLAN switching and tagging based on the protocols being used. Disadvantage is that the protocol must be robust enough to maintain the switched network.

15.Complete the table for the commands used to configure a VLAN on a 2900 series Catalyst switch.

Command PurposeSwitch#show version Displays the version of IOS running on the

switchSwitch#vlan database Enter the VLAN configuration modeSwitch(vlan)#vlan [vlan number] Assign a number to the VLAN to createSwitch(config)#interface [type] [port] Identify which interface to assign VLAN toSwitch(config-if)#switchport access vlan [vlan number]

Assign VLAN to one or more interfaces

Switch#show vlan [brief] Verify VLAN assignment(s)Switch#show vlan id [vlan number] Verify VLAN assignmentSwitch#show running-config Display the switch’s configuration fileSwitch(vlan)#no vlan [vlan number] Delete a VLANSwitch#show spanning-tree Display the spanning tree topology known

to the routerSwitch#debug sw-vlan packets Display general information about VLAN

packets that the router received but is not configured to support

16.What are the steps you should follow to troubleshoot problems with your VLANs?

1. Check the physical indications, such as LED status. 2. Start with a single configuration on a switch and work outward. 3. Check the Layer 1 link. 4. Check the Layer 2 link. 5. Troubleshoot VLANs that span several switches.

17.What is a broadcast storm?

A broadcast storm occurs when a large number of broadcast packets are received on a port. Forwarding these packets can cause the network to slow down or to time out. Storm control is configured for the switch as a whole, but operates on a per-port basis. By default, storm control is disabled.


18.How can they be prevented?

By the use of high and low thresholds to discard excessive broadcast, multicast, and unicast MAC traffic. Also the switch can be set to shut down the port when the rising threshold is reached.



1. What is the definition of a trunk in a switched network?

A physical and logical connection between two switches across which network traffic travels. A trunk is a single transmission channel between two points that are usually switching centers.

2. What is a trunk designed to do if there are multiple VLANs in a network?

The purpose of a trunk is to save ports when creating a link between two devices implementing VLANs, typically two switches.

3. What are trunking protocols designed to do? What are the two types of trunking mechanisms? Which has become the standard? Why?

To effectively manage the transfer of frames from different VLANs on a single physical line. The trunking protocols establish agreement for the distribution of frames to the associated ports at both ends of the trunk. Trunking mechanisms: frame filtering and frame taggingFrame tagging has been adopted as the standard trunking mechanism by IEEE because it is more scalable than frame filtering.

4. How does frame tagging work?

Frame tagging places a unique identifier in the header of each frame as it is forwarded throughout the network backbone. The identifier is understood and examined by each switch before any broadcasts or transmissions are made to other switches, routers, or end-station devices. When the frame exits the network backbone, the switch removes the identifier before the frame is transmitted to the target end station. Frame identification functions at Layer 2 and requires little processing or administrative overhead.

5. What is the first step you must perform on a switch before starting trunking?

Configure the port first as a trunk and then specify the trunk encapsulation


6. Complete the following table:

Command PurposeSwitch(config-if)#switchport mode trunk Turns on trunking modeSwitch(config-if)#switchport trunk

encapsulation [dot1q | isl]Specifies encapsulation type on port with either 802.1a or ISL

Switch#show port capabilities Displays what the port can do, including what encapsulation the port can support

Switch#show trunk [mod_num/port_num] Displays if trunking has been configured and the settings

Switch#erase startup-configuration Clears NVRAM of any saved configuration files

Switch(vlan)#vtp v2-mode Sets the VTP version to Version 2Switch(vlan)#vtp domain [name] Creates a management domainSwitch#show vtp status Displays VTP configuration and statusSwitch(vlan)#vtp [client | server | transparent] Sets the correct mode of the switchSwitch#show vtp counters Displays statistics about advertisements

sent and received on the switchRouter(config)#interface fastethernet [port-

number.subinterface-number]Identifies which port and/or subinterface you wish to configure

Router(config-if)#encapsulation dot1q [vlan-number]

Set encapsulation for 802.1q on an interface

Router(config-if)#ip address [ip-address] [subnet-mask]

Sets the IP address on an interface

7. What does it mean if the trunking mode has been set to “negotiate”?

Puts the port into permanent trunking mode but prevents the port from generating Dynamic Trunking Protocol (DTP) frames. You must configure the neighboring port manually as a trunk port to establish a trunk link.

8. What is VTP? Why should it be used on a VLAN’ed network?

VLAN Trunking Protocol (VTP) was created to solve potential operational problems in a VLANs network switched environment. The role of VTP is to maintain VLAN configuration consistency across a common network administration domain. VTP is a messaging protocol that uses OSI Layer 2 trunk frames to manage the addition, deletion, and renaming of VLANs on a single domain. Further, VTP allows for centralized changes that are communicated to all other switches in the network.

9. What is a VTP domain?

A VTP domain is made up of one or more interconnected devices that share the same VTP domain name.


10.What are the four items found in a VTP message?

VTP protocol version: Either Version 1 or 2 VTP message type: Indicates one of four types Management domain name length: Indicates size of the name that follows Management domain name: The name configured for the management

domain

11.What are the three modes that switches can work in when running VTP? Briefly describe each one.

Server - can create, modify, and delete VLAN and VLAN configuration parameters for the entire domain. VTP servers send VTP messages out to all trunk ports.

Client - cannot create, modify, or delete VLAN information. VTP clients do process VLAN changes and send VTP messages out to all trunk ports.

Transparent - forward VTP advertisements such as version 2, but ignore information contained in the message. A transparent switch will not modify its database when updates are received, nor will the switch send out an update indicating a change in its VLAN status. Except for forwarding VTP advertisements, VTP is disabled on a transparent switch.

12.What are the two types of VTP advertisements?

Requests from clients that want information at bootup Response from servers

13.What are the three types of VTP messages?

Advertisement requests Summary advertisements Subset advertisements

14.What kinds of activities can trigger a VTP advertisement?

Creating or deleting a VLAN, suspending or activating a VLAN, changing the name of a VLAN, changing the maximum transmission unit (MTU) of a VLAN

15.What are the two versions of VTP available now? Which is the default version? Are they interoperable?

Version 1 and Version 2. Version 1 is the default; they are not interoperable.


16.Can VLANs communicate directly with one another? Why or why not?

No, they must still go through a router to communicate. Routers are designed to connect networks, which is what VLANs are.

17.What is meant by “a router on a stick”?

A trunk line, which can support multiple VLANs, is the physical connection to a router. This topology is called a router on a stick because there is a single connection to the router. However, there are really multiple logical connections between the router and the switch, based on how many VLANs run through the trunk.

18.What is a “subinterface”? How are they used on a switch?

The logical division of a physical interface into several logical interfaces. Each subinterface of a port can support a separate VLAN and is assigned a different IP address.


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CCNA 3 Study Guide Answers-All