CPE 400 Midterm
What are some attributes of TCP flow control?
- receiver "advertises" free buffer space by including rwnd value in TCP header of receiver-to-sender segments - sender limits amount of unacked ("in-flight") data to receiver's rwnd value -guarantees receive buffer will not overflow
What is the difference between iterative and recursive DNS query? a) Iterative does not provide caching capabilities b) Recursive puts the burden on the contacted server c) Iterative puts the burden on the local DNS server d) All of the above
b or c
1 second is equivalent to a) 1000 microseconds b) 1000 milliseconds c) 100 milliseconds d) 1000000 milliseconds
b) 1000 milliseconds
TCP segment has mandatory ________________ bytes long header. a) 16 b) 20 c) 24 d) 30
b) 20
If the ACK value is 201, then byte _______ has been received successfully. a) 201 b) 200 c) 202 d) None of the above
b) 200
If a packet size is 2500 bits and the rate at which a router can pump out packets is 5 Mega bits per second, then the transmission delay in milliseconds is: a) 10 milliseconds b) 500 microseconds c) 1 second d) None of the above
b) 500 microseconds (L/R)
What type of DNS query returns an IP address? a) MX b) A c) CNAME d) NS
b) A
Which of the following 5 components must be part of reliable data transfer protocol? a) Checksum, Timer, Congestion control, Acknowledgement and Pipelining b) Checksum, Timer, Sequence number, Acknowledgement and Pipelining c)Checksum, Sequence number, Congestion-control,Flow control and Acknowledgement d) Timer, Sequence number, Congestion control, Flow control and Acknowledgement
b) Checksum, Timer, Sequence number, Acknowledgement and Pipelining
In which layer of the network stack is the packet is called segment? a) Application Layer b) Transport Layer c) Network Layer d) Link Layer
b) Transport Layer
Which layer(s) is/are responsible for causing congestion in the network? a) Application Layer b) Transport Layer c) Network Layer d) All of the above
b) Transport layer
In terms of different communication methodology, there are a) unicasting and broadcasting b) unicasting, broadcasting and multicasting c) broadcasting, multicasting and flooding d) broadcasting, multicasting and selective flooding
b) unicasting, broadcasting and multicasting
Which port is NOT used by default by FTP? a) 20 b) 21 c) 25 d) None of the above
c) 25
Which statement is true about the resource record of type CNAME? a) It stores the IP address of a server b) It is used mostly for SMTP relaying c) It is an alias name for some canonical name d) None of the above
c) It is an alias for some canonical name
In TCP, the size of the transmission window is the ________ of rwnd and cwnd. a) Maximum b) Sum c) Minimum d) Subtraction difference
c) Minimum
The time required to examine the packet's header and determine where to direct the packet is part of a) Transmission delay b) Queuing delay c) Nodal Processing delay d) None of the above
c) Nodal processing delay
The time required to examine the packet's header and determine where to direct the packet is part of a) Transmission delay b) Queuing delay c) Nodal processing delay d) None of the above
c) Nodal processing delay
For a packet, the time required to travel from one router to another is called a) Transmission delay b) Queuing delay c) Propagation delay d) All of the above
c) Propagation delay
Which of the following is a correct statement? a) Router works in all 5 layers of protocol stack b) Router has only one IP address c) Routers build the backbone of the Internet d) Routers examine packets up to transport layer
c) Routers build the backbone of the Internet
For the following event at receiver, what would be TCP receiver's action? Event: arrival of out-of-order segment higher-than-expect seq. # . Gap detected. TCP receiver action: a) Delayed ACK. Wait up to 500ms for next segment. If no next segment, send ACK. b) Send cumulative ACK, ACKing both in-order segments, indicating seq. # of next expected byte. c) Send duplicate ACK, indicating seq. # of next expected byte. d) Do not take any action.
c) Send duplicate ACK, indicating seq. # of next expected byte.
Assume a client is establishing communication with a server through a 3-way TCP handshake protocol. In this connection establishment phase, when the server is responding, which of the six flags (U, A, P, R, S, F) will be set by the server? a. U and A b. S c. A and S d. A and P
c. A and S
Which of the following protocols uses different ports for control and data messages? a) Hyper text transfer protocol b) Real time protocol c) Simple mail transfer protocol d) File transfer protocol
d) File transfer protocol
Which of the following is not a function of application layer? a) routing b) flow-control c) congestion-control d) all of the above
d) all of the above
In the layer hierarchy as the data packet moves from the upper to the lower layers, in the network layer, the packet is called a) message b) segment c) frame d) datagram
d) datagram
What are some services of DNS?
hostname to IP address translation host aliasing mail server aliasing load distribution
Authoritative DNS
organization's own DNS server(s), providing authoritative hostname to IP mappings for organization's named hosts
What does Closed state signify?
represents no connection state at all.
When is congestion avoidance phase used?
when cwnd >= ssthresh, window grows linearly
Which statement is true about the resource record of type A? a) It stores the IP address of a server b) It is used mostly for SMTP relaying c) It is an alias name for some canonical name d) None of the above
a) it stores the IP address of a server
Transport layer decapsulates data from a) network layer b) link layer c) application layer d) physical layer
a) network layer
Which one of the following is NOT a function of transport layer? a) routing b) flow-control c) congestion control d) All of the above
a) routing
In the congestion detection algorithm, if detection is by a time-out, a new _______ phase starts a) slow start b) congestion avoidance c) congestion detection d) none of the above
a) slow start
UDP header size
8 bytes
What is the difference between iterative and recursive DNS query?
Iterative: puts burden of name resolution on local DNS server no or low load at upper levels of hierarchy No caching of DNS information in upper levels of hierarchy Recursive: puts burden of name resolution on contacted name server heavy load at upper levels of hierarchy advantage of caching of DNS information in upper levels of hierarchy
What are some differences between TCP and UDP?
TCP - reliable transport, flow control, congestion control, connection-oriented UDP- unreliable data transport, connection-less, does not provide reliable transport, flow control or congestion control.
TCP Reno
TCP Reno differs from TCP Tahoe at congestion avoidance. When triple duplicate ACKs are received, it will halve the congestion window, perform a fast retransmit, and enters fast recovery.
What are the two congestion control strategies?
TCP Tahoe TCP Reno
What does Listen state signify?
The server is waiting for an incoming call
What does Established state signify?
Normal data transfer state
What does Syn-Sent state signify?
The client has started to open a connection
What does UDP stand for?
User Datagram Protocol
What does Last-Ack state signify?
Wait for pending packets
What does Time-Wait state signify?
Wait for pending packets
When is slow-start phase used?
When cwnd < ssthresh, window grows exponentially
TCP assigns a sequence number to each segment that is being sent. The sequence number for each segment is number of the __________ byte carried in that segment. a) first b) second c) middle d) last
a) first
type=CNAME
name is alias for some canonical name value is canonical name
type=NS
name is domain value is hostname of authoritative name server for domain
type=A
name is hostname value is IP address
What happens when there is a loss by 3 duplicate ACKs?
- CWND is cut in half - Threshold is cut in half
What happens when there is a loss by timeout?
- CWND is cut to 1 - Threshold is cut in half
recursive query
-puts burden of name resolution on contacted name server -heavy load at upper levels of hierarchy?
How many states does TCP (client and server) have?
11- Listen Syn-Sent Syn-Received Established Fin-Wait-1 Fin-Wait-2 Close-Wait Closing Last-Ack Time-Wait Closed
What are some HTTP response status codes?
200 - OK 301 - Moved Permanently 400 - Bad Request 404 - Not Found 505 - Version not supported
What does Syn-Received state signify?
A connection request has arrived
3-Way Handshake (TCP)
A: SYN B: SYN ACK A: ACK
Wireshark promiscuous mode
Allows us to see all packets going to a network.
What are the 5 layers of Networking?
Application, Transport, Network, Link, Physical
What does Closing state signify?
Both sides have tried to close simultaneously
Why would we choose an alpha value closer to 0 in EstimatedRTT formula?
Choosing alpha-value close to 0 makes the weighted average respond to changes very quickly
Why would we choose an alpha value closer to 1 in EstimatedRTT formula?
Choosing alpha-value close to 1 makes the weighted average immune to changes that last a short time
What does Fin-Wait-1 state signify?
Client has said it's finished
What does DNS stand for?
Domain Name System
top-level domain
Domains (including .net, .org, .com, .mil. and the set .xx country codes) at the end of a domain name are the highest level of the domain name hierarchy.
What does FTP stand for?
File Transfer Protocol
What are the two generic forms of pipelining?
Go-back-N and Selective repeat
What does HTTP stand for?
Hypertext Transfer Protocol
What does IoT stand for?
Internet of Things
What is IDS?
Intrusion Detection System
What is an elastic app?
Make use of whatever throughput they get.
Does handshaking occur in UDP?
No
What are the four components of delay in networking? Why does packet loss happen?
Nodal Processing, Queuing, Transmission and Propagation delay Router queue (aka buffer) has finite capacity. Packets arriving to full queue will be dropped resulting in packet loss. Packet loss can also happen due to link failure or node failure.
What are some differences between persistent and non-persistent HTTP?
Persistent- multiple objects can be sent over single TCP connection between client, server. HTTP 1.1 Includes GET, POST, HEAD, DELETE, PUT Non-Persistent- at most one object sent over TCP connection, the connection is then closed. HTTP 1.0 Includes GET, POST, HEAD
What does Fin-Wait-2 state signify?
Server has agreed to release
What does Close-Wait state signify?
Server has initiated a release
What does SMTP stand for?
Simple Mail Transfer Protocol
What does TCP stand for?
Transmission Control Protocol
EstimatedRTT formula
[(1-α)*EstimatedRTT] + (α*SampleRTT)
What is Wireshark?
a protocol analyzer or packet sniffer
8 Mbps is equivalent to a) 1 MBps b) 8000 bps c) 8000 KBps d) None of the above
a) 1 MBps
For the following events at TCP receiver, what should be the TCP receiver action? a) arrival of in-order segment with expected seq. #. All data up to expected seq # already ACKed b) arrivial of out-of-order segment higher-than-expected seq #. Gap detected
a) Delayed ACK. Wait up to 500ms for next segment. If no next segment, send ACK b) Immediately send duplicate ACK, indicating seq. # of next expected byte
Why is it difficult to secure IoT devices? a) Heterogeneous products not having a clear standardization for security protocols b) The devices have IP addresses and/or link layer addresses and can connect to the Internet c) The devices are everywhere d) None of the above
a) Heterogeneous products not having a clear standardization for security protocols
By definition, Bluetooth is an example of a) Personal area Network b) Private area Network c) Public area Network d) None of the above
a) Personal area network
Which is a correct statement about TLD servers? a) Responsible for .com, .org, .edu, and per country domain such as .fr, .jp b) Because of its infrastructure does not use caching c) It s the first server to be contacted if there is no cached answered d) None of the above
a) Responsible for .com, .org, .edu, and per country domain such as .fr, .jp
The domain name system is maintained by a) Several companies that form a distributed database system b) The Federal Communications Commission c) A company authorized by the government d) None of the above
a) Several companies that form a distributed database system
What does TCP stand for? a) Transmission Control Protocol b) Transport Control Protocol c) Transport Communication Protocol d) Transmission Communication Protocol
a) Transmission Control Protocol
Which is an example of local area network? a) Wi-Fi b) Bluetooth c) WiMax d) none of the above
a) Wi-Fi
User datagram protocol is called connectionless because a) all UDP packets are treated independently by transport layer b) it sends data as a stream of related packets c) both a and b d) none of the mentioned
a) all UDP packets are treated independently by transport layer
Iterated query
contacted server replies with name of server to contact
DNS databases contain a) Name server records b) Hostname-to-address records c) Hostname aliases d) All of the above
d) All of the above
Which statement is true about the structure of the Internet a) Its core is made of several ISPs b) A packet can travel through multiple ISPs before reaching its destination c) There are several levels (tiers) of ISPs, Tier-1 being the largest ones d) All of the above
d) All of the above
TCP Tahoe
detect loss through a timeout. Loss signaled by timeout, threshold = ½ current congestion window, congestion window set to 1 MSS. Go all the way back to slowstart when there's a timeout
What are some attributes of DNS?
distributed database- implemented in hierarchy of many name servers application-layer protocol: hosts, name servers communicate to resolve names (address/name translation)
What is pipelining?
sender allows multiple, "in-flight" , yet-to-be acknowledged pkts
What does it "stateless" mean in HTTP?
server maintains no information about past client requests
Why is Checksum used?
to detect bit errors in a transmitted packet
type=MX
value is name of mailserver associated with name
