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Computer Networking Final
Exam ALL QUIZ/MIDTERM
QUESTIONS 2024-2025.
Graded A+
____ Forwarding is the responsibility of ____ plane while ____ is responsibility of ____ plane. - ANS1. packet. 2. data 3. routing
- control "store-and-forward" technology is used by - ANSpacket switched networks 3-Way handshake has the following paket sequence: - ANS1. SYN, 2. SYN-ACK, 3. ACK A HTTP server has two types of sockets. Name and describe them. - ANSPassive socket is one that is set up and is just listening for connections, and will establish one when found. Active socket is one that actually does data transfer. ACK segments consume _______ sequence number(s) and are they acknowledged? - ANS0; they are not An ARP query packet is encapsulated in.... - ANSa Link-Layer broadcast frame Assume you freshly rebooted your machine and connected to the internet and typed "http://google.com" in the browser. By the time Google's home page is loaded, how many ARP requests are made by your machine? - ANSOne. Assuming a single non- persistent connection, how long does it take to to download a very small object from a server? What about 3 very small objects? - ANS1 object: 2 RTT (Round trip time) 3 objects: 6 RTT
CNAME records gives an ______ to a hostname - ANSalias Common HTTP response codes: 200 indicates... 301 indicates... 404 is... 500 is ... Possibilities : Server Error, Success, Not Found, Bad Request, Client Error,Redirection,Packet Loss - ANS200 : Success! 301: Redirection 404: Not Found 500: Bad Request Complexity in the internet is at the ________ of the network. - ANSedge!!!!! Connection establishment in TCP is called __________ handshaking - ANS3-way handshaking Consider a 125 KB file that needs to be sent through a network path. The bandwidth of the path is 1 Mbps. The one way delay between sender and receiver is 20 ms. Suppose the sender continuously sends data at the bandwidth rate, and no packets are lost, no retransmissions. How long does it take to send the file? And the throughput of the network is? 1KB = 1000Bytes - ANS125* 1000
- 8 = 1000000 bits or 1 Mb So on a path with bandwidth 1Mbps ( 1 Mb per second) it would take roughly 1 second to transmit the file. The throughput of the network is 1 Mbps. Consider a 125 KB file that needs to be sent through a network path. The bandwidth of the path is 1 Mbps. The one way delay between sender and receiver is 20 ms. Suppose the sender needs to wait for an ACK after sending every 1 KB packet (that means we have a congestion window size of 1). Assume ACK also takes 20 ms to come back. How long does it take to send the file? ___ seconds. And the throughput of the network is ___ Kbps. If we
services to the network layer: - ANSError Detection. Ethernet runs on what media: - ANSFiber Co-axial cables Unshielded twisted pair (UTP) For Ethernet, if an adapter determines that a frame it has just received is addressed to a different adapter....
- ANSIt discards the frame. Given the TCP header structure, which TCP port numbers are valid port numbers? 123456 1234 65700 63123 12345 1234567 - ANS123456 Correct! 1234 65700 Correct! 63123 Correct! 12345 1234567 Host A and Host B are communicating over a TCP connection. Host B has already received 130 bytes from Host A. Now Host A sends two more segments back to back containing 30 and 80 bytes respectively.
- What is the sequence number of the first segment? 2. What is the sequence number of the second segment? - ANS1. 131 2. 161 How many hosts can be added to a subnet with the subnet mask 128.1.1.1/28? - ANS2^(32 - subnet(28)) = 2^4 = 16 HTTP 1.0 protocol supports following methods: - ANSGET, HEAD, POST If HTTP is stateless, how is security (login) and shopping experience implemented in web sites? - ANSTo implement security and suggestive advertising, 'cookies' are sent from the web server to the client. Both the client and the web server keep record of these cookies, and with this unique identifier web servers can determine the appropriate content to be pushed to each user. If the ACK value is 200, then which byte has been received successfully. - ANS199 In SR (Selective
Repeat) protocol, is it possible for the sender to receive ACK for a packet that is outside of the current window. (packets 1,2,3,4,5,6,7,8,9.... window size is 3, current window is 7,8,9. Is it possible to receive ACK for 1 or 2 or ... or 6 at sender? Consider ACK losses, retransmission and duplicate ACKs) Please explain. - ANSYes, in Selective Repeat the receiver's window is not linked to the sender's acknowledgement window. So if, for instance, a packet were to delay past the RTT time for that sequence, but was not lost, and another packet and acknowledgement were to get back beforehand, then an ACK could arrive for a packet outside of the current window. In TCP, the receiver can temporarily shut down the window; the sender, however, can always send a segment of _____ byte(s) after the window is shut down. - ANSone In the 'rdt' protocol developed in the class, what is the purpose of the sequence number? - ANSTo handle duplicates. If a packet of the same sequence number is found, the receiver can throw it out. In the 'rdt' protocol developed in the class, what is the purpose of the timer? - ANSThe timer serves the purpose of monitoring not yet acknowledged segments. If a segment reaches a timeout before being acknowledged, it will be re transmitted. in the 5 layer network we are studying in the class, name the layers in the correct order - ANSApplication Transport Network Data Link Physical Knowing that TCP uses a 32-bit sequence number field,
generates chunks of 40 bytes of data every 20 msec, and each chunk gets encapsulated in a TCP segment and then an IP datagram. What percentage of each datagram will be overhead, and what percentage will be application data? - ANSTCP header + IP datagram = 40 bytes.... 50% overhead, 50% data T/F: Before sending a packet into the internet, the source must determine all of the links that packet will traverse between source and destination. - ANSFalse T/F: Connections in a UDP application starts with a 3-way handshake - ANSFALSE! UDP is the sending of information with no handshake to a destination. This is why it is unreliable. T/F: Consider a queue preceding a transmission link of rate R. Suppose a packet arrives to the queue periodically every 1/a seconds. Also suppose all packets are of length L. Then the queuing delay is small and bounded as long as aL < R. - ANSTrue! R is bits or bytes per second, so if a packet is L bits/bytes long, and it passing the transmission link at rate 1/a seconds... T/F: Consider an HTTP Web server using persistent connections. Suppose the server spawns a separate process for each client that connects to the server. Then each of these spawned processes will have different server port numbers. - ANSFalse! The server uses the client side ip and port to determine what to respond to and where to send a response. T/F: Consider the switched LAN architecture. Assuming all links are full duplex,
there are never collisions in this LAN. - ANSTrue T/F: CRC error detection, as used in Ethernet, is always able to detect whether there is an error in a frame. - ANSFalse! It is not suited to help against intentional attacks. CRC is not authenticated, so the CRC can be regenerated for intentionally altered data and it will not detect this. T/F: Each LAN adapter has a unique IP address. - ANSFalse! T/F: Each LAN adapter has a unique LAN address. - ANSTrue!! T/F: Every autonomous system must use the same intra-autonomous system routing algorithm. - ANSFalse! T/F: In a distance-vector routing algorithm, each node has a map of the entire network and determines the shortest path from itself to all other nodes in the network. - ANSFalse! T/F: In a virtual- circuit packet-switched network, a packet switch maintains state information for each connection passing through the router. - ANSTrue! T/F: In the BGP routing algorithm, each AS advertises to its neighbors its estimates of the shortest distances from the AS to all possible destination ASs. - ANSFalse! T/F: Layers four and five of the Internet protocol stack are implemented in the end systems but not in the routers in the network core. - ANSTrue, Layers 4 and 5 are the Application and Transport layers T/F: OSPF uses BGP for routing among areas. - ANSFalse! BGP is used for inter-AS routing, while OSPF is used for intra-AS routing. In intra-AS routing, OSPF uses link-state algorithms, calculating routes using
number of useful bits delivered at the receiver, and is different from but related to to the bandwidth of the link. - ANSTrue! TCP assigns a sequence number to each segment that is being sent. The sequence number for each segment is the number of the _______ byte carried in that segment. - ANSFirst. TCP Service Provides: - ANSReliable Transport, Flow Control, Connection oriented, Congestion contol The link-state algorithm has the following properties: - ANS1. it determines the shortest path from the source node to all other nodes. 2. it requires the source node to know the costs between every pair of adjacent nodes in the graph. 3. after the kth iteration, the least-cost paths are known to k nodes The value of the acknowledgment field in a segment defines the number of the ______byte a receiver expects to receive. - ANSNext! The value of window size is determined by _________. - ANSthe reciever Two main attributes that measure the performance of a network are.... - ANSThroughput and Delay UDP service: - ANSUnreliable, used in gaming applications We know HTTP is a stateless protocol. Explain what is the meaning of a stateless protocol. - ANS'Stateless' protocols are those that do not store any information about the data being passed through it. For example, if I were to use bare HTTP to talk to many web pages that suggest me products or advertisements, there would be no way for the web pages to recognize me, as HTTP is stateless.
Only with additional features, such as cookies, can web servers have knowledge of who I am and what I have browsed in the past. What is the TCP/UDP checksum of the following two numbers 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 0 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 - ANS0100010001000011 add all bits, carry ones left over around and add again, and one's compliment. What is true for HTTP: - ANSIt can be both non-persistent and persistent, it uses tcp, and is stateless. What lines can ONLY appear in a SERVER code (cannot appear in client code). - ANS-s.listen(5) -s.accept() When a switch transmits an Ethernet frame, the Ethernet frame has.... - ANSThe original MAC address of the source interface. Which DNS record gives the IP of a host? - ANS'A' Which is a broadcast ip address? - ANS255.255.255.255 Which of the following are valid MAC addresses: 1A-2F-BB-76-09-AD FF-FF-FF-FF-FF-FF 1A-2F-BB-76-09-ZZ 1A-2F-BB-76 - ANS1 and 2 Which of the following ip addresses are invalid ip addresses (select all that apply)? 251.252.253.254 256.255.254. 250.250.1.250 128.1.1.1 - ANS256.255.254.253 is the only incorrect address. Which of the following IP addresses are not publically routable? 10.10.2.2 163.10.3.4 3.10.20.30 10.1.1.1 - ANSThe Internet Assigned Numbers Authority (IANA) reserves the following IP address blocks for use as private IP addresses: 10.0.0.0 to 10.255.255.255. 172.16.0.0 to 172.31.255.255. 192.168.0.0 to 192.168.255.255 So option 1 and 4 are not
