200-301 : Cisco Certified Network Associate (CCNA) : Part 20

200-301 : Cisco Certified Network Associate (CCNA) : Part 20

1. Refer to the network diagram in the exhibit. Host A is configured with an incorrect default gateway. All other computers and the Router are known to be configured correctly (Click the Exhibit(s) button.)

   

   Which of the following statements is TRUE?

   • Host C on Network A cannot communicate with Host A on Network A.
   • Host A on Network A can communicate with all other hosts on Network A.
   • Host A on Network A can communicate with Router R.
   • Host C on Network A cannot communicate with Router R.
   • Host D on Network B cannot communicate with Host B on Network A.
   Explanation:
   Host A on Network A can communicate with all other hosts on Network A and with Router R. To communicate with local hosts and the interface of Router R (which are all in the same subnet) only a correct IP address is required. If the default gateway of Host A is incorrect, then it will not be able to communicate with any host on the other side of the router, which includes Network B in the diagram. Packets from hosts on Network B will reach Host A on Network A without any problem, because they possess the correct address of the default gateway or router, but Host A will send the packet to a dead end because Host A has an incorrect default gateway. On the other hand, Host A does not require a default gateway to communicate with other hosts on same network.

   Host C on Network A WILL be able to communicate with Host A on Network A , even though Host A has an incorrect default gateway because Host A and C are in the same subnet, which requires no use of the of the gateway or router..

   Host C on Network A WILL be able to communicate with Router R because Host C has the correct default gateway address which is the address of Router R.

   Host D on Network B WILL be able to communicate with Host B on Network A because both hosts have a correct default gateway address.

   Objective:
   Routing Fundamentals
   Sub-Objective:
   Troubleshoot basic Layer 3 end-to-end connectivity issues

2. What is the Institute of Electrical and Electronics Engineers (IEEE) specification for Spanning Tree Protocol (STP)?

   • 802.1d
   • 802.1q
   • 802.3u
   • 802.3z
   Explanation:
   The IEEE specification for STP is 802.1d. STP uses the spanning-tree algorithm to find and prevent loops in redundant network topologies. This helps mitigate broadcast storms, multiple copies of frames, and Media Access Control (MAC) address database inconsistencies.

   The IEEE committee developed the 802.1 series of specifications for bridging. The IEEE 802.1q specification is for Virtual LAN (VLAN) trunking. Per this specification, a 4-byte 802.q header, which contains the Priority and VLAN ID fields, is inserted in the middle of the original Ethernet header.

   802.3 is the IEEE committee specification that defines the Ethernet group. Ethernet is a LAN protocol that specifies physical layer and MAC sublayer media access. IEEE 802.3 uses carrier sense multiple access collision detect (CSMA/CD) to provide access for many devices on the same network. 802.3u is the IEEE specification for Fast Ethernet. 802.3z is the IEEE specification for Gigabit Ethernet.

   Objective:
   LAN Switching Fundamentals
   Sub-Objective:
   Configure, verify, and troubleshoot STP protocols

3. When transmitting to a remote destination, what two things will occur after a host has determined the IP address of the destination to which it is transmitting? (Choose two.)

   • The sending host will perform an ARP broadcast in its local subnet using the IP address of the destination host.
   • The sending host will perform an ARP broadcast in its local subnet using the IP address of the local router interface.
   • The local router interface will respond with the MAC address of the destination host.
   • The local router interface will respond with its own MAC address. 
   • The destination host will respond with its own MAC address.
   Explanation:
   When a transmission is made to a remote location, the sending host will perform an Address Resolution Protocol (ARP) broadcast in its local subnet using the IP address of the local router interface, and the local router interface will respond with its own MAC address. A remote address is defined as an address in a different subnet.

   When a host determines (through a process called ANDing) that a destination address is remote, it will send the packet to the local router interface, which is known as the default gateway on the host. But when it performs ANDing on the IP address of the local router interface, it will discover that the interface is local. When transmitting to a local IP address, a conversion to a MAC address must occur. Therefore, it will perform a local ARP broadcast, and the local router interface will respond with its MAC address.

   Regardless of whether the host is broadcasting for the MAC address of the destination locally on the same LAN, or if it is broadcasting for the MAC address of the router interface (remotely), the broadcast will be a Layer 2 broadcast using the MAC address ff-ff-ff-ff-ff. It will be received by all devices on the LAN, but only the device with the specified IP address will reply.

   The ARP resolution process does take a second or two to complete if no mapping for the destination devices IP address to MAC address is found in the ARP cache. For example, if the MAC address must be resolved through the ARP broadcast when pinging from one device to another, it can cause the first several echo requests to go unanswered, as shown on the output below. After this resolution has been completed, however, the second ping attempt should receive an answer to all five ICMP echo requests.

   Router1#ping 50.6.3.26
   
   Type escape sequence to abort
   Sending 5, 100-byte ICMP Echos to 50.6.3.26, timeout is 2 seconds:
   ..!!!
   
   Router1#ping 50.6.3.26
   
   Type escape sequence to abort
   Sending 5, 100-byte ICMP Echos to 50.6.3.26, timeout is 2 seconds:
   !!!!!

   The sending host will not perform an ARP broadcast in its local subnet using the IP address of the destination host. A local ARP broadcast is only performed when the ANDing process deduces that the destination IP address is local. In this case, the destination is remote.

   The destination host will not respond with its MAC address. The process of learning the MAC address of the destination computer is the responsibility of the local router interface on the subnet where the destination host resides.

   Objective:
   LAN Switching Fundamentals
   Sub-Objective:
   Describe and verify switching concepts

4. Which command enables HSRP on an interface?

   • hsrp
   • standby ip
   • standby mode hsrp
   • switchport mode hsrp
   Explanation:
   The standby ip interface configuration command enables Hot Standby Router Protocol (HSRP). The syntax for this command is as follows:

   switch(config-if)# standby group-number ip ip-address

   The group-number argument specifies the HSRP group number on the interface. You do not need to enter a group number if there is only one HSRP group.

   At least one interface on one of the routers in the group must be configured with the virtual IP address of the group. It is optional on all other interfaces on the other routers, which can learn the address through the hellos sent among the group.

   A complete HSRP configuration is shown below with an explanation of each command.

   RouterA (config) #interface Fa0/1 
   RouterA (config-if) # ip address 192.168.5.6 255.255.255.0 
   RouterA (config-if) # standby 2 ip 192.168.5.10 
   RourerA(config-if) # standby 2 priority 150 
   RouterA (config-if) #standby 2 Preempt 
   RouterA(config-if) #standby 2 track interface fa0/2

   – Line 1 specifies the interface
   – Line 2 addresses the interface
   – Line 3 specifies the HSRP group number and the virtual IP address
   – Line 4 sets the HSRP priority
   – Line 5 allows the router to take the active role if its priority becomes higher than that of the active router

   In the above, the router is tracking its own Fa0/2 interface. If that interface goes down it will reduce its priority by 10 (this is the default decrement when not specified). The new value would be 140 if that happened. To specify a decrement value, add it to the track command, as in this example: track interface Fa0/2 20.

   When you configure routers to be part of an HSRP group, they listen for the HSRP MAC address for that group as well as their own burned-in MAC addresses.

   HSRP uses the following MAC address:
   0000.0c07.ac** (where ** is the HSRP group number)

   The switchport mode interface configuration command will configure the VLAN membership mode of a port. It is not used to enable HSRP.

   The options standby mode hsrp and hsrp are not valid commands.

   Objective:
   Infrastructure Services
   Sub-Objective:
   Configure, verify, and troubleshoot basic HSRP

5. What IOS command produced the following output?

   

   • show interface mac
   • show mac
   • show mac-address-table
   • show ip interface
   Explanation:
   The output was produced by the show mac-address-table command. The show mac-address-table command displays a table of every learned MAC address and the switch port associated with the MAC address. The output shown in the question indicates that four MAC addresses have been learned by this switch, and the last column indicates the switch port over which each MAC address was learned, and for which frames destined for each MAC address will be forwarded. The MAC address table is built dynamically by examining the source MAC address of received frames.

   The show ip interface command is a router command, and displays no information on MAC address tables.

   The show interface mac and show mac commands are incorrect because they are not valid Cisco IOS commands.

   Objective:
   LAN Switching Fundamentals
   Sub-Objective:
   Describe and verify switching concepts

6. You know that Router2 is configured for RIP. Which Cisco Internetwork Operating System (IOS) command is used to view the current state of all active routing protocols?

   • show ip arp
   • debug ip rip
   • show ip protocols
   • show ip routing process
   • show arp
   • show interfaces
   Explanation:
   The show ip protocols command is used to view the current state of active routing protocols. This command is issued from Privileged EXEC mode. The syntax of the command is as follows:

   Router2# show ip protocols

   Output of the command would resemble the following:

   

   This command shows additional information about individual protocols. The version number of RIP being used is shown on the seventh line of the output. This output also indicates on lines 12-14 that it is routing for three networks: 201.19.0.0, 16.2.0.0, and 10.3.0.0. This means that the router will be sending and receiving RIP updates on any interfaces that have IP addresses in those networks.

   Also note that the router at 16.2.0.10 has not sent an update in 3 minutes and 10 seconds. If an update is not received in 50 seconds (for a total of 4 minutes), the route-flush timer (240 seconds from the last valid update) will have expired, causing the local router to remove all networks learned from the router at 16.2.0.10 from the routing table.

   For more specific information about those interfaces, in terms such as S0 or Fa0/0, you could execute the show ip interface brief command as shown below. The output displays the addresses of the interfaces, which would indicate which interfaces were enabled for RIP and thus sending and receiving updates.

   

   The show ip arp command is incorrect because this command is executed on a router to determine the IP and MAC addresses of hosts on a LAN connected to the router.

   The debug ip rip command is incorrect because this command is used to capture RIP traffic between the routers in real time. This command could also be used to determine the version of RIP being used as shown in line 2 of the partial output of the command below:

   Router2#debug ip rip
   RIP protocol debugging is on

   *Mar 3 02:11:39.207:RIP:received packet with text authentication 234
   *Mar 3 02:11:39.211:RIP:received v1 update from 122.108.0.10 on Serial0
   *Mar 3 02:11:39.211:RIP: 79.0.0.0/8 via 0.0.0.0 in 2 hops
   *Mar 3 02:11:40.212:RIP: ignored v2 packet from 192.168.5.6 (illegal version)

   In the above output Router 2 has received a version 1 update from a router at 122.108.0.10 which indicates that a ping to that router should succeed. It also shows what was learned from the router at 122.108.0.10, which is the router to network 79.0.0.0/8 via 0.0.0.0. The 0.0.0.0 indicates that the next hop for that route is the router that sent this advertising (the router at 122.108.0.10).

   The output also shows that a RIP router at 192.168.5.6 sent a version 2 update that was ignored by Router 2, which is using version 1. This mismatch of versions will prevent Router 2 from forming an adjacency with the router at 192.168.5.6.

   Note: Before running any debug command you should execute the show processes command and verify that the CPU utilization on the router is low enough to handle the effects of running the debug command.

   The show ip routing process command is incorrect because it is not a valid Cisco IOS command.

   The show arp command is used to identify the IP address to MAC address mappings the router has leaned through the ARP broadcast process. It is helpful when you have identified errors associated with a MAC address and you need to learn the IP address or vice versa. Sample output is below.

   router# show arp
   Protocol Address Age (min) Hardware Addr Type Interface
   Internet 10.0.0.3 0 0004.dd0c.ffcb ARPA Ethernet01
   Internet 10.0.0.1 - 0004.dd0c.ff86 ARPA Ethernet0

   The difference between the show arp command and the show ip arp command is that show arp will also include mappings learned through non-IP protocols such as when inverse ARP is used to learn and map DLCIs to IP addresses.

   The show interface command can also be used to identify IP addresses from MAC addresses and vice versa, but also indicates the state of the interface; IP addresses MTU and much more about each interface. Sample output is below.

   router# show interfaces
   Ethernet 0 is up, line protocol is up
   Hardware is MCI Ethernet,address is 0000.0c00.750c(bia 0000.0c00.750c)
   Internet address is 10.108.28.8, subnet mask is 255.255.255.0
   MTU 1500 bytes, BW 10000 Kbit, DLY 100000 usec, rely 255/255, load 1/255

   Objective:
   Routing Fundamentals
   Sub-Objective:
   Interpret the components of routing table

7. You apply the following commands to a router named R2:

   R2(config)# interface Tunnel1
   R2(config-if)# ip address 172.16.1.2 255.255.255.0
   R2(config-if)# ip mtu 1400
   R2(config-if)# ip tcp adjust-mss 1360
   R2(config-if)# tunnel source 2.2.2.2
   R2(config-if)# tunnel destination 1.1.1.1

   Which statement is NOT true with regard to this configuration?

   • The physical IP address of R2 is 2.2.2.2
   • The connection will operate in IP mode
   • The configuration will increase packet fragmentation
   • The configuration alters the maximum segment size
   Explanation:
   The configuration will not increase packet fragmentation. Conversely, it will reduce it by lowering the maximum transmission unit to 1400 and the maximum segment size to 1360 bytes.

   Most transport MTUs are 1500 bytes. Simply reducing the MTU will account for the extra overhead added by GRE. Setting the MTU to a value of 1400 is a common practice, and it will ensure unnecessary packet fragmentation is kept to a minimum.

   The other statements are true. The physical address of R2 is 2.2.2.2, while the tunnel interface address is 172.16.1.2.

   Because you have not issued any command that changes the connection, it will operate in the default mode of IP.

   The configuration does alter the maximum segment size with the ip tcp adjust-mss 1360 command.

   Objective:
   WAN Technologies
   Sub-Objective:
   Configure, verify, and troubleshoot GRE tunnel connectivity

8. Which Cisco IOS command configures the clock rate to 64,000 bits per second on an interface?

   • clock-rate 64000
   • clock rate 64k
   • clock rate 64000
   • clockrate 64000
   Explanation:
   The clock rate 64000 command would configure the clock rate to 64,000 bits per second on an interface. The clock rate command is used to configure the clock rate for hardware connections on serial interfaces. These interfaces can be network interface modules (NIMs) and interface processors. The syntax of this command is clock rate bps.

   A serial connection between two routers that are connected with a v.35 serial cable requires a clock rate on the Data Communications Equipment (DCE) end of the cable, but not on the Data Terminal Equipment (DTE) end. When the router is connected to a CSU/DSU for connection to the outside world, the DCE end will be the CSU/DSU. In a lab environment or any situation where you have two routers connected with this type of serial cable, a clock rate must be set on the DCE end of the cable.

   When troubleshooting a connection of this type between routers, the state of the clock rate (set or unset) can be determined by running the show controllers command on the DCE end. The output will display as follows if the clock rate is NOT set:

   Router#show controllers s0/0
   Interface Serial0/0
   Hardware is PowerQUICC MPC860
   DTE V.35 clocks stopped
   More output omitted

   Notice the DTE V.35 clocks stopped line, which indicates no clock rate is set. Another clue that there is a Layer 2 problem is the output of the show ip interface S0/0 command, executed on the same interface below:

   Router# show ip interface s0/0
   Serial0/0 is up, line protocol is down
   Internet address is 192.168.1.2/24
   Broadcast address is 255.255.255.255

   Notice the Serial0/0 is up, line protocol is down line. Serial0/0 is up indicates that the physical connection is good, but line protocol is down indicates a problem with Layer 2 . If you were troubleshooting from the bottom layer to the top, you would now check Layer 2, which would be the clock rate.

   If you want to change a DCE interface to a DTE device, you should use the no clock rate command.

   All the other options are incorrect because these commands are syntactically incorrect.

   Objective:
   WAN Technologies
   Sub-Objective:
   Describe WAN access connectivity options

9. Which switch will be selected as the root bridge by Spanning Tree Protocol (STP)?

   • switch with lowest bridge ID 
   • switch with lowest IP address
   • switch with lowest Media Access Control (MAC) address
   • switch with lowest number of root ports
   Explanation:
   STP will use elections to arrive at a fully converged state that will ensure a switching loop free network. It will select:
   – The root bridge
   – The root port on each non-root bridge
   – Designated ports on any shared segments with no direct connection to the root bridge.

   The switch with the lowest bridge ID will be selected as the root bridge by STP. A bridge ID has two components: the priority number and the MAC address. On Cisco devices, the priority number may range from 0 to 65535. The priority number constitutes the most significant bits of the bridge ID. If you want to ensure that a particular switch in a topology always becomes a root bridge, regardless of the MAC address, you can set the priority number of that switch to the lowest value among all switches in the topology.

   Since the selection of the root bridge influences all other decisions and thus the single loop free path for each VLAN, the selection and location of the root bridge is important and best not left to chance. Once you have determined the best switch for the role of root bridge, you can ensure its election by lowering its bridge priority.

   It is best for the root bridge to be centrally located with respect to the clients and the servers that generate the most traffic on the VLAN. For example, in the diagram below, if most of the traffic travels between the clients and the servers on VLAN 20, the best choice for the root bridge for VLAN 20 would be SwitchD. SwitchD is centrally located between the clients on VLAN 20 and the servers on VLAN 20.

   

   To illustrate the type of inefficient traffic that could occur when care is not given to the location of the root bridge, consider the diagram above and assume that Switch B was chosen the root bridge. Next, assume that traffic needs to go from VLAN 10 connected to Switch C to VLAN 10 connected to Switch A. The shortest path would be from Switch C to Switch A. However, because the only port that is forwarding on Switch C is the port that leads to the root bridge (Switch B), then the actual path would be from Switch C, to Switch B, to Switch E, and then to Switch A.

   By default, the priority number of all Cisco switches is configured to a value of 32768. For example, consider three switches in network topology with the following MAC addresses and the same default priority number:

   0000.0B02.AAAA
   0000.0B02.BBBB
   0000.0B02.CCCC

   The switch with the lowest MAC address, 0000.0B02.AAAA, will become the root bridge.

   The switch with the lowest IP address will not be selected as the root bridge by STP because the IP address of the switch does not influence the selection of the root bridge.

   The switch with the lowest MAC address will not be selected as the root bridge by STP. A combination of priority number and MAC address determines the selection of the root bridge. The MAC address will determine the root bridge only if there is a tie for the switch with the lowest priority number.

   The switch with the lowest number of root ports will not be selected as the root bridge by STP. Root ports are the interfaces on non-root bridges. On a non-root bridge, the least-root-cost interface is known as a root port. Therefore, the switch having the fewest root ports is not the root bridge.

   Objective:
   LAN Switching Fundamentals
   Sub-Objective:
   Configure, verify, and troubleshoot STP protocols

10. Which command would be used to list the timers, version of spanning tree and the bridge ID of the local and designated switch for a specific VLAN on a Cisco Catalyst 2950 series switch?

    • show spanning-tree vlan vlan-id
    • show vlan database
    • show vlan vlan-id
    • show vlan brief
    Explanation:
    The show spanning-tree vlan vlan-id command is correct because this command shows timers, version of spanning tree, and the bridge ID of the local and designated switches for a specific VLAN on a Cisco Catalyst 2950 series switch.

    The show vlan id vlan-id command is incorrect because it will show only the ports assigned to each VLAN.

    The show vlan database command is incorrect because this is not a valid Cisco IOS command.

    The show vlan brief command is incorrect because this command is used view the entire VLAN database, and does not provide information for a specific VLAN.

    Objective:
    Infrastructure Management
    Sub-Objective:
    Use Cisco IOS tools to troubleshoot and resolve problems

11. Which of the following commands sets the local router to serve as an authoritative time source?

    • ntp server
    • ntp master
    • ntp authenticate
    • ntp peer
    Explanation:
    The ntp master command sets the local router to serve as an authoritative time source.

    The ntp server command is used to specify an external time source that the local router should use as its time source.

    The ntp authenticate command is used to enable the authentication of time source to which the local router has been configured to use. It is the first step in a process that must also include the specification of a hashing algorithm and a key, both of which must match on the time source.

    The ntp peer command is used to configure the local router to synchronize a peer or to be synchronized by a peer. It does not make the local router authoritative as a time source like the ntp master command.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure and verify NTP operating in a client/server mode

12. Which two are TRUE of straight-through cable? (Choose two.)

    • The wires on the cable are crossed over.
    • It is also known as a patch cable.
    • You can connect two routers using a straight-through cable.
    • You can connect a hub to a switch using a straight through cable.
    • You can connect a switch to a router using a straight through cable.
    Explanation:
    A straight-through cable is also known as a patch cable, and a straight-through cable is used to connect a switch to a router. The following are the characteristics of a straight-through cable:
    – It is a twisted-pair copper wire cable.
    – The RJ-45 connectors at both ends have the same conductor arrangement.
    – It is also known as a patch cable.
    – You can connect a switch to a router using a straight-through cable.
    – You can connect a router to a hub or a workstation to a hub using a straight-through cable.
    All the other options are incorrect because they are the characteristics of a crossover cable.

    Objective:
    Network Fundamentals
    Sub-Objective:
    Select the appropriate cabling type based on implementation requirements

13. File Transfer Protocol (FTP) and Simple Mail Transfer Protocol (SMTP) work at which layer in the Open Systems Interconnection (OSI) model?

    • the Session layer
    • the Presentation layer
    • the Application layer
    • the Network layer
    Explanation:
    FTP and SMTP work at the application layer in the OSI model. The application layer is responsible for interacting directly with the application. It provides application services, such as e-mail and FTP. The following protocols work on the application layer:
    – FTP: Used to transfer data between hosts through the Internet or a network.
    – SMTP: A Transmission Control Protocol (TCP)/ Internet Protocol (IP) protocol used to send and receive e-mail messages.
    – Telnet: Used to allow remote logins and command execution.

    The Session layer is incorrect because this layer creates, manages, and terminates sessions between communicating nodes. NetBIOS and Session Control Protocol (SCP) work at the session layer.

    The Presentation layer is incorrect because this layer enables coding and conversion functions for application layer data. The Presentation layer includes graphic image formats, such as Graphics Interchange Format (GIF), Joint Photographic Experts Group (JPEG), and Tagged Image File Format (TIFF).

    The Network layer is incorrect because this layer defines the network address or the Internet Protocol (IP) address, which are then used by the routers to make forwarding decisions.

    Objective:
    Network Fundamentals
    Sub-Objective:
    Compare and contrast OSI and TCP/IP models

14. A packet is received with a destination IP address of 10.2.16.10. What would the next hop IP address be for this packet?

    

    • 192.168.1.10
    • 192.168.4.2
    • 192.168.10.254
    • None; the packet will be dropped.
    Explanation:
    The packet will be routed to the next hop IP address of 192.168.4.2, since this routing table entry is the most specific match for the remote network. Packets are routed according to the most specific, or “longest,” match in the routing table.

    The packet in the scenario has a destination IP address of 10.2.16.10, which matches two entries in the routing table.
    – 10.0.0.0 /8: this matches based on the /8 mask, where only the first byte has to match. The destination IP address of 10.2.16.10 has a first byte matching 10. If this were the only matching route table entry, it would be selected.
    – 10.2.16.0 /24: The first 24 bits of this entry match the first 24 bits of the destination IP address of 10.2.16.10.

    Therefore, the 10.2.16.0 /24 entry is selected for routing this packet because it most specifically matches the destination IP address, or has the longest number of matching bits.

    The next hops of 192.168.1.10 and 192.168.10.254 will not be used, as these routes are not the most specific matches for the destination IP address of the packet.

    It is interesting to note that packets that are destined for the 10.2.32.0 network will be load balanced across both serial 0/0 and serial 0/1 because the cost (2172425) is the same for both paths.

    The packet will not be dropped because there is at least one routing table entry that matches the destination IP address of the packet.

    To ensure that no packets are dropped, even if there is no matching route in the routing table, a default route could be configured as follows (next hop picked at random for illustration):

    Router(config)# ip route 0.0.0.0 0.0.0.0 192.168.1.1

    This configuration would instruct the router to send any packets that do match the existing routes to 192.168.1.1. For example, a packet destined for 201.50.6.8/24 would not match any routes in the table, and would thus be forwarded to 192.168.1.1.

    If you understand how routing tables and routing advertisements work, it is relatively simple to describe the contents of a router’s routing table without seeing the table directly. To do so, you would view the router’s configuration and the configuration of its neighbors using show run, along with a diagram of its network connections. For example, examine the diagram of the two routers shown below along with their respective configurations:

    

    

    It will contain S*0.0.0.0/0 [1/0] via 192.35.87.5 because of the static default route indicated in line 4 of its configuration output.

    It will contain R 192.168.110.128/26 [120/1] via 192.35.87.5 00:00:22, Serial 0/0 because Router 2 has a network 192.168.110.128 statement indicating that it will advertise this network to its neighbors.

    It will contain the two routes C 192.35.87.4/30 is directly connected, S0/0 and C 192.168.54.64/26 is directly connected, Fa0/0 because all directly connected routes are automatically placed in the table.

    Objective:
    Routing Fundamentals
    Sub-Objective:
    Interpret the components of routing table

15. Which three statements are TRUE regarding a Local Area Network (LAN)? (Choose three.)

    • A LAN is confined to one building or campus. 
    • A LAN can cover great distances.
    • A LAN provides fast data transmission.
    • A LAN is easily expandable.
    • LANs require the use of a router to communicate between local hosts.
    Explanation:
    A LAN is confined to one building or campus, provides fast data transmission, and is easily expandable. A LAN refers to the interconnection of computers within a building or a group of buildings. A LAN generally uses twisted pair cables for data transmission.

    The following are some characteristics of LANs:
    – LANs are generally confined to a building, a group of buildings, or a campus.
    – Every computer in the LAN can communicate with every other computer on the network.
    – A LAN is easy to set up, as physical connectivity can be easily established.
    – The cost of the transmission medium used is low, as a LAN generally uses CAT5, CAT5e, or CAT6 cables for data transmission.
    – A LAN provides fast data transmission rates.

    The option stating that a LAN can cover great distances is incorrect. A Wide Area Network (WAN) is a network that does not have any geographical boundaries. The Internet is the best example of a WAN.

    LANs do not require the use of a router to communicate (although they can be used to connect subnets) between local hosts. Hosts can communicate through a hub or switch.

    Objective:
    Network Fundamentals
    Sub-Objective:
    Compare and contrast network topologies

16. A router is running several routing protocols, and as a result has learned three routes to the 192.168.5.0 network. Below are the details about the three learned routes:

    

    Based on this information, which route will be placed in the routing table?

    • the RIP route
    • the OSPF route
    • the EIGRP route
    • all of the routes
    Explanation:
    The EIGRP route will be placed in the routing table. When a router learns multiple routes to a network from different routing table population methods, which includes routes from routing protocols and static routes created by the administrator, it does so in two steps:
    – It selects the route with the lowest administrative distance.
    – If multiple routes exist with equal administrative distance (usually meaning they learned from the same routing protocol), it chooses from the routes by selecting the one with the lowest cost.

    Since EIGRP has the lowest default administrative distance (90), the EIGRP route will be chosen.

    The RIP route will not be chosen because it has a default administrative distance of 120.

    The OSPF route will not be chosen because it has a default administrative distance of 110.

    Objective:
    Routing Fundamentals
    Sub-Objective:
    Describe how a routing table is populated by different routing information sources

17. How will SwitchB handle the frame it just received?

    

    • It will forward the frame out all ports
    • It will forward the frame out FastEthernet0/4 only
    • It will drop the frame
    • It will record the source MAC address
    • It will forward the frame out FastEthernet0/10 only
    Explanation:
    SwitchB will forward the frame out FastEthernet0/10 only. The MAC address table indicates that the switch has the destination MAC address in its table and the destination is located on switch port FastEthernet 0/10, therefore it will switch the frame to that interface.

    It will not forward the frame out all ports. It will only do that when it receives a frame for which it knows no destination and then it will forward it out all ports except the one on which it arrived. For example if it were sending a frame to 00c0.5658.d26e, which is nowhere to be found in the table and the frame arrived on port FastEthernet0/10 it would send the frame to very port except FastEthernet0/10.

    It will not forward the frame out FastEthernet0/4. The MAC address located on that port is 00c0.57ce.ce33, which means that is the port on which the frame arrived.

    It will not drop the frame. It will not drop the frame when it has the destination in its MAC table.

    It will record the source MAC address. That address is already present in the table.

    Objective:
    LAN Switching Fundamentals
    Sub-Objective:
    Describe and verify switching concepts

18. Which of the following features is used with the ip nat inside command to translate multiple devices in the internal network to the single address in the IP address pool?

    • static
    • override
    • overload
    • dynamic
    Explanation:
    The overload keyword, when specified with the ip nat inside command, translates multiple devices in the internal network to a single address in the IP address pool.

    For example:

    ip nat pool test 172.28.15.1 172.28.15.1 prefix 24

    In this example, the NAT pool named “test” only has a range of one address. Another variation of this command is as follows:

    ip nat inside source list 3 interface serial 0 overload

    This command configures NAT to overload on the address assigned to the serial 0 interface.

    When this variation is used, the command uses a list named 3 to determine the addresses in the pool

    With static NAT, translation mappings are created statically and are placed in the translation tables regardless of whether there is traffic flowing.

    With dynamic NAT, the translation mappings table is populated as the required traffic flows through NAT-enabled devices.

    Override is not a valid NAT option. There is no such option.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Configure, verify, and troubleshoot inside source NAT

19. Which feature enables a host to obtain an IP address from a DHCP server on another subnet?

    • DHCP relay agent
    • DHCP BOOTP agent
    • DHCP relay protocol
    • DHCP BOOTP relay
    Explanation:
    A Dynamic Host Configuration Protocol (DHCP) relay agent enables hosts to obtain IP addresses from a DHCP server on another subnet. Hosts use DHCPDISCOVER broadcast messages to locate the DHCP server because they don’t know the location of the DHCP server. Because routers are designed to filter broadcasts, the DHCPDISCOVER packet would be dropped unless the router is configured to forward such packets. Enabling a DHCP relay agent on a Cisco router allows it to receive certain types of broadcasts and forward them to special helper addresses.

    The following sequence describes an IP address relay process:
    – The DHCP client broadcasts a DHCP request on the network.
    – The DHCP request is intercepted by the DHCP relay agent, which inserts the relay agent information option (option 82) in the packet.
    – The DHCP relay agent forwards the DHCP packet to the DHCP server.
    – The DHCP server uses the suboptions of option 82 in the packet, assigns IP addresses and other configuration parameters, and forwards the packet to the client.
    – The relay agent again intercepts the packet and strips off the option 82 information before sending it to the client.

    The ip helper-address interface configuration command enables a DHCP relay agent on a Cisco router.

    DHCP is an enhancement over Bootstrap Protocol (BOOTP) and is used to automate the distribution of IP address to clients from a central server. The BOOTP protocol was also used distribute IP addresses, but was inflexible to changes in the network. DHCP offers three advantages that also address the inflexibility of the BOOTP protocol:
    – Automatic allocation of permanent IP addresses
    – Automatic allocation of time bound (leased) IP addresses
    – Ability to assign static IP address or define a pool of reserved IP address

    When a DHCP relay is unnecessary, the following steps describe the address allocation process:
    – The client device broadcasts a DHCPDISCOVER broadcast message to locate a DHCP server.
    – The DHCP server replies with a DHCPOFFER unicast message containing configuration parameters, such as an IP address, a MAC address, a domain name, and a lease for the IP address for the client device.
    – The client sends back a DHCPREQUEST broadcast, which is a formal request for the offered IP address to the DHCP server.
    – The DHCP server replies back to client device with DHCPACK unicast message, acknowledging the allocation of the IP address to this client device.

    While DHCP is very useful in reducing the administrative burden of issuing IP configurations in a large network, Cisco best practices call for using static IP addressing in a small (6 or fewer hosts) network.

    All other options are invalid devices or features.

    Objective:
    Infrastructure Services
    Sub-Objective:
    Troubleshoot client- and router-based DHCP connectivity issues

20. What is the default administrative distance of a static route?

    • 90
    • 0
    • 1
    • 110
    Explanation:
    While the administrative distance of a route can be altered, there are default administrative distance values assigned to various methods of learning routes. When a static route is defined, it will have an administrative distance of 1.

    An administrative distance value of 90 is the default assigned to EIGRP.

    An administrative distance value of 0 is the default assigned to directly connected routes.

    An administrative distance value of 110 is the default assigned to OSPF.

    Objective:
    Routing Fundamentals
    Sub-Objective:
    Describe how a routing table is populated by different routing information sources