CCNA Modules 8-10: Communicating Between Networks - Exam Answers
42. Which three commands are used to set up secure access to a router through a connection to the console interface?
1. Line console 0; 2. Login; 3. Password Cisco (the three commands needed to password protect the console port are as follows: 1. Line console 0; 2. Password Cisco; 3. Login. The interface fastethernet 0/0 command is commonly used to access the configuration mode used to apply specific parameters such as the IP address to the Fa0/0 port. The line vty 0 4 command is used to access the configuration mode for Telnet. The 0 and 4 parameters specify ports 0 through 4, or a maximum of five simultaneous Telnet connections. The enable secret command is used to apply a password used on the router to access the privileged mode).
4. Which IPv4 address can a host use to ping the loop back interface?
127.0.0.1
59. What property of ARP causes cached IP-to-MAC mappings to remain in memory longer?
Entries in an ARP table are time-stamped and are purged after the timeout expires.
19. When transporting data from real-time applications, such as streaming audio and video, which field in the IPv6 header can be used to inform the routers and switches to maintain the same path for the packets in the same conversation?
Flow Label. (The Flow Label in IPv6 header is a 20-bit field that provides a special service for real-time applications. This field can be used to inform routers and switches to maintain the same path for the packet flow so that packets will not be reordered).
62. What property of ARP allows hosts on a LAN to send traffic to remote networks?
Local hosts learn the MAC address of the default gateway.
49. Which term describes a field in the IPv4 packet header used to identify the next protocol?
Protocol
57. Which term describes a field in the IPv4 packet header used to identify the next level protocol?
Protocol
17. What routing table entry has a next hop address associated with a destination network?
Remote routes
5. A computer can access devices on the same network but cannot access devices on other networks. What is the probable cause of this problem?
The computer has an invalid default gateway address
37. A router boots and enters setup mode. What is the reason for this?
The configuration file is missing from NVRAM.
10. Within a production network, what is the purpose of configuring a switch with a default gateway address?
The default gateway address is used to forward packets originating from the switch to remote networks. (A default gateway address allows a switch to forward packets that originate on the switch to remote networks. A default gateway address on a switch does not provide Layer 3 routing for PCs that are connected on that switch. A switch can still be accessible from Telnet as long as the source of the Telnet connection is on the local network).
66. What property of ARP causes the request to be flooded out all ports of a switch except for the port receiving the ARP request?
The destination MAC address FF-FF-FF-FF-FF-FF appears in the header of the Ethernet frame.
68. What property of ARP causes the NICs receiving an ARP request to pass the data portion of the Ethernet frame to the ARP process?
The type field 0x806 appears in the header of the Ethernet frame.
12. Which field in the IPv4 header is used to prevent a packet from traversing a network endlessly?
Time-to-live. ( the value of the Time-to-Live (TTL) field in the IPv4 header is used to limit the lifetime of a packet. The sending host sets the initial TTL value; which is decreased by one each time the packet is processed by a router. If the TTL field decrements to zero, the router discards the packet and sends an Internet Control Message (ICMP) Time Exceeded message to the source IP address. The Differentiated Services (DS) field is used to determine the priority of each packet. Sequence Number and Acknowledgement Number are two fields in the TCP header).
27. What is the aim of an ARP spoofing attack?
To associate IP addresses to the wrong MAC address.
1. Which information is used by routers to forward a data packet toward its destination?
Destination IP address
6. Which statement describes a feature of the IP protocol?
IP relies on upper layer services to handle situations of missing or out-of-order packets. (IP protocol is a connection-less protocol, considered unreliable in terms of end-to-end delivery. It does not provide error control in the cases where receiving packets are out-of-order or in cases of missing packets. It relies on upper layer services, such as TCP, to resolve these issues).
50. Which term describes a field in the IPv4 packet header that contains an 8-bit binary value used to determine the priority of each packet?
Differentiated services
14. What IPv4 header field identifies the upper layer protocol carried in the packet?
Protocol. (It is the Protocol field in the IP header that identifies the upper-layer protocol the packet is carrying. The Version field identifies the IP version. The Differential Services field is used for setting packet priority. The Identification field is used to reorder fragmented packets).
51. Which term describes a field in the IPv4 packet header that contains a 32-bit binary value associated with an interface on the sending device?
Source IPv4 address
55. Which term describes a field in the IPv4 packet header used to limit the lifetime of a packet?
TTL
26. Which two types of IPv6 messages are used in place of ARP for address resolution?
1. Neighbor solicitation; 2. Neighbor advertisement (IPv6 does not use ARP. Instead, ICMPv6 neighbor discovery is used by sending neighbor solicitation and neighbor advertisement messages).
47. What are two potential problems that can result from ARP operation?
1. On large networks with low bandwidth, multiple broadcasts could caused data communication delays; 2. Network attackers could manipulate MAC address mappings in ARP messages with the intent of intercepting network traffic. (Large numbers of ARP broadcast messages could cause momentary data communication delays. Network attackers could manipulate MAC address and IP address mappings in ARP messages with the intent to intercept network traffic. ARP requests and replies cause entires to be made into the ARP table, not the MAC address table. ARP table overflows are very unlikely. Manually configuring static ARP associations is a way to prevent, not facilitate, ARP poisoning and MAC address spoofing. Multiple ARP replies resulting in the switch MAC address table containing entires that match the MAC addresses of connected nodes and are associated with the relevant switch port are required for normal switch frame forwarding operations. It is not an ARP caused network problem).
44. Which two functions are primary functions of a router?
1. Packet forwarding; 2. Path selection (a router accepts a packet and accesses its routing table to determine the approximate exit interface based on the destination address. The router then forwards the packet out of that interface).
9. What are two services provided by the OSI network layer?
1. Routing packets toward the destination; 2. Encapsulating PDUs from the transport layer. (The OSI network layer provides several services to allow communication between devices: 1. Addressing; 2. Encapsulation; 3. Routing; 4. De-encapsulating; 5. Error detection; 6. Placing frames on the media; 7. And Collision detection are all functions of the data link layer).
21. Under which two circumstances will a switch flood a frame out of every port except the port that the frame was received on?
1. The frame has the broadcast address as the destination address; 2. The destination address is unknown to the switch. (A switch will flood a frame out of every port, except the one that the frame was received from, under two circumstances. Either the frame has the broadcast address as the destination address, or the destination address is unknown to the switch).
36. What are two functions of NVRAM?
1. To retain contents when power is removed; 2. To store the startup configuration file. (NVRAM is permanent memory storage, so the startup configuration file is preserved even if the router loses power).
60. What property of ARP allows MAC addresses of frequently used servers to be fixed in the ARP table?
A static IP-to-MAC address entry can be entered manually into an ARP table.
61. What property of ARP allows MAC addresses of frequently used servers to be fixed in the ARP table?
A static IP-to-MAC address entry can be entered manually into an ARP table.
29. Where are IPv4 address to Layer 2 Ethernet address mappings maintained on a host computer?
ARP cache
20. What statement describes the function of the Address Resolution Protocol?
ARP is used to discover the MAC address of any host on the local network.
7. Why is NAT not needed in IPv6?
Any host or user can get a public IPv6 network address because the number of available IPv6 addresses is extremely large.
39. What happens when the transport input ssh command is entered on the switch vty lines?
Communication between the switch and remote users is encrypted. (The transport input ssh command when entered on the switch vty (virtual terminal lines) will encrypt all inbound controlled telnet connections).
11. What is a basic characteristic of the IP protocol?
Connection-less. (Internet Protocol (IP) is a network layer protocol that does not require initial exchange of control information to establish an end-to-end connection before packets are forwarded. Thus, IP is connection-less and does not provide reliable end-to-end delivery by itself. IP is media independent: user data segmentation is a service provided at the transport layer).
3. A router receives a packet from the Gigabit 0/0 interface and determines that the packet needs to be forwarded out the Gigabit 0/1 interface. What will the router do next?
Create a new Layer 2 Ethernet frame to be sent to the destination
54. Which term describes a field in the IPv4 packet header that contains a unicast, multicast, or broadcast address?
Destination IPv4 address
30. What important information is examined in the Ethernet frame header by a Layer 2 device in order to forward the data onward?
Destination MAC address. (The Layer 2 device, such as a switch, uses the destination MAC address to determine which path (interface or port) should be used to send data onward to the destination device).
13. What is one advantage that the IPv6 simplified over IPv4?
Efficient packet handling. (The IPv6 simplified header offers several advantages over IPv4: 1. Better routing efficiency and efficient packet handling for performance and forwarding-rate scalability; 2. No requirement for processing checksums; 3. Simplified and more efficient extension header mechanisms (as opposed to the IPv4 Options field); 4. A Flow Label field for per-flow processing with no need to open the transport inner packet to identify the various traffic flows).
32. A network administrator has been asked to enter a banner message on a Cisco device. What is the fastest way a network administrator could test whether the banner is properly configured?
Exit privileged EXEC mode and press Enter. (While at the privileged mode prompt such as Router#, type exit, press Enter, and the banner message appears. Power cycling a network device that has had the banner mold command issued will also display the banner message, but this is not a quick way to test the configuration).
23. Which destination address is used in the ARP request frame?
FFFF.FFFF.FFFF (The purpose of an ARP request is to find the MAC address of the destination host on an Ethernet LAN. The ARP process sends a Layer 2 broadcast to all devices on the Ethernet LAN. The frame contains the IP address of the destination and the broadcast MAC address, FFFF.FFFF.FFFF. The host with the IP address in the ARP request will reply with a unicast frame that includes the MAC address of the host. Thus the original sending host will obtain the destination IP and MAC address pair to continue the encapsulation process for data transmission).
52. Which term describes a field in the IPv4 packet header used to detect corruption in the IPv4 header?
Header checksum
24. A network technician issues the arp -d* command on a PC after the router that is connected to the LAN is reconfigured. What is the result after this command is issued?
The ARP cache is cleared. (Issuing the arp -d* command on a PC will clear the ARP cache content, this is helpful when a network technician wants to ensure the cache is populated with updated information).
16. What information does the loop back test provide?
The TCP/IP stack on the device is working correctly.
18. How do hosts ensure that their packets are directed to the correct network destination?
They have to keep their own local routing table that contains a route to the loop back interface, a local network route, and a remote default route.
45. What is the effect of using the Router# copy running-config startup-config command on a router?
The contents of NVRAM will change. (The command copy running-config startup-config copies the running-configuration file from RAM into NVRAM and saves it as the startup-configuration file. Since the NVRAM is none-volatile memory it will be able to retain the configuration details when the router is powered off).
64. What property of ARP forces all Ethernet NICs to process an ARP request?
The destination MAC address FF-FF-FF-FF-FF-FF appears in the header of the Ethernet frame.
46. What will happen if the default gateway address is incorrectly configured on a host?
The host cannot communicate with hosts in other network. (When a host sends a message to another host located on the same network, it can forward the message directly. This is because the data link frame address of the remote destination host cannot be used directly. Instead, the IP packet has to be sent to the router (default gateway) and the router will forward the packet toward its destination. Therefore, if the default gateway is incorrectly configured, the host can communicate with other hosts on the same network, but not with hosts on remote networks).
8. Which parameter does the router use to choose the path to the destination when there are multiple routes available?
The lower metric value that is associated with the destination network
2. A computer has to send a packet to a destination host in the same LAN. How will the packet be sent?
The packet will be sent directly to the destination host
65. What property of ARP causes a reply only to the source sending an ARP request?
The source MAC address appears in the header of the Ethernet frame.
38. The global configuration command ip default-gateway 172.16.100.1 is applied to a switch. What is the effect of this command?
The switch can be remotely managed from a host on another network. (A default gateway address is typically configured on all devices to allow them to communicate beyond just their local network. In a switch this is achieved using the command ip default-gateway).
67. What property of ARP causes the NICs receiving an ARP request to pass the data portion of the Ethernet frame to the ARP process?
The type of field 0x906 appears in the header of the Ethernet frame
22. Which statement describes the treatment of ARP requests on the local link?
They are received and processed by every device on the local network. (One of the negative issues with ARP requests is that they are sent as a broadcast. This means all devices on the local link must receive and process the request).
56. Which term describes a field in the IPv4 packet header that contains a 4-bit binary value set to 0100?
Version
58. Which term describes a field in the IPv4 packet header that contains a 4-bit binary value set to 0100?
Version
