CCNA CyberOps Chapter 4 Exam Online

Hint

When received at the physical layer of a host, the bits are formatted into a frame at the data link layer. A packet is the PDU at the network layer. A segment is the PDU at the transport layer. A file is a data structure that may be used at the application layer.

Hint

The encapsulation process is performed at each OSI layer and is the process of placing one message format inside another message format.

Hint

The binary format for 255.255.255.224 is 11111111.11111111.11111111.11100000. The prefix length is the number of consecutive 1s in the subnet mask. Therefore, the prefix length is /27.

Hint

ANDing allows us to identify the network address from the IP address and the network mask.

Hint

The IP address 192.168.25.10 is an IPv4 private address. This address will not be routed over the Internet, so school A will not be able to reach school B. Because the address is a private one, it can be used freely on an internal network. As long as no two devices on the internal network are assigned the same private IP, there is no IP conflict issue. Devices that are assigned a private IP will need to use NAT in order to communicate over the Internet.

Hint

The private IP addresses are within these three ranges:
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255

Hint

In the compressed format, the :: represents two contiguous hextets of all zeros. Leading zeros in the second, fifth, and sixth hextets have also been removed.

Hint

The purpose of ICMP messages is to provide feedback about issues that are related to the processing of IP packets.

Hint

When router R1 receives the ICMP echo requests from host A it will forward the packets out interface G0/1 towards host B. However, before forwarding the packets, R1 will encapsulate them in a new Ethernet frame using the MAC address of interface G0/1 as the source and the MAC address of host B as the destination.

Hint

When a network device wants to communicate with another device on the same network, it sends a broadcast ARP request. In this case, the request will contain the IP address of PC2. The destination device (PC2) sends an ARP reply with its MAC address.

Hint

When a node encapsulates a data packet into a frame, it needs the destination MAC address. First it determines if the destination device is on the local network or on a remote network. Then it checks the ARP table (not the MAC table) to see if a pair of IP address and MAC address exists for either the destination IP address (if the destination host is on the local network) or the default gateway IP address (if the destination host is on a remote network). If the match does not exist, it generates an ARP broadcast to seek the IP address to MAC address resolution. Because the destination MAC address is unknown, the ARP request is broadcast with the MAC address FFFF.FFFF.FFFF. Either the destination device or the default gateway will respond with its MAC address, which enables the sending node to assemble the frame. If no device responds to the ARP request, then the originating node will discard the packet because a frame cannot be created.

Hint

Large numbers of ARP broadcast messages could cause momentary data communications 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 entries 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 entries 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.

Hint

Because FTP uses TCP as its transport layer protocol, sequence and acknowledgment numbers will identify the missing segments, which will be re-sent to complete the message.

Hint

A socket is a combination of the source IP address and source port or the destination IP address and the destination port number.

Hint

TCP:
· Provides tracking of transmitted data segments
· Destination devices will acknowledge received data.
· Source devices will retransmit unacknowledged data.

UDP
· Destination devices will not acknowledge received data
· Headers use very little overhead and cause minimal delay.​

Hint

TCP segments are acknowledged by the receiver as they arrive. The receiver keeps track of the sequence number of received segments and uses the sequence number to reorder the segments and to identify any missing segments that need to be retransmitted.

Hint

TCP uses the 3-way handshake. UDP does not use this feature. The 3-way handshake ensures there is connectivity between the source and destination devices before transmission occurs.

Hint

The DHCPDISCOVER message is sent by a DHCPv4 client and targets a broadcast IP along with the destination port 67. The DHCPv4 server or servers respond to the DHCPv4 clients by targeting port 68.

Hint

The components of the URL http://www.cisco.com/index.htm are as follows:
http = protocol
www = part of the server name
cisco = part of the domain name
index = file name
com = the top-level domain

Hint

NAT was developed to conserve IPv4 addresses. A side benefit is that NAT adds a small level of security by hiding the internal network addressing scheme. However, there are some drawbacks of using NAT. It does not allow true peer-to-peer communication and it adds latency to outbound connections.

Hint

From the perspective of a NAT device, inside global addresses are used by external users to reach internal hosts. Inside local addresses are the addresses assigned to internal hosts. Outside global addresses are the addresses of destinations on the external network. Outside local addresses are the actual private addresses of destination hosts behind other NAT devices.

Hint

The Wireshark capture is of a DNS query from PC-A to the DNS server. Because the DNS server is on a remote network, the PC will send the query to the default gateway router, router DG, using the MAC address of the router G0/0 interface on the router.

Hint

The GET command is a client request for data from a web server. A PUT command uploads resources and content, such as images, to a web server. A POST command uploads data files to a web server.

Hint

A TCP/IP segment that originated on the PC has 192.168.1.2 as the IP source address. 2578 is the only possible option for the source port number because the PC port number must be in the range of registered ports 1024 to 49151. The destination is the web server, which has the IP address 192.168.2.2, and the destination port number is 80 according to the HTTP protocol standard.