Networks final
Select the proper equation for TCP's calculation of EstimatedRTT.
EstimatedRTTn = (1 - a)*EstimatedRTTn-1 + a*SampleRTTnew
Bus Ethernet uses a random access scheme.
True
For a 10Mbps link, 1000 bit times is 0.1ms.
True
ICMP messages are carried within the payload of IP datagrams.
True
IPv6 datagrams cannot be converted to IPv4 datagrams without losing any information.
True
In IPv6, there is no datagram fragmentation performed in the network core..
True
NAPT devices translate IP address and port numbers.
True
TCP has a congestion control mechanism.
True
TCP implements network fairness indirectly.
True
The "ping" application (on Windows) uses ICMP echo request/reply.
True
The "traceroute" application (on Windows) receives ICMP messages.
True
The "traceroute" application (on Windows) sends ICMP messages by default.
True
The IPv6 address size is 128 bits.
True
The IPv6 header does not have a checksum.
True
The Internet Protocol (IP) header may be 28 bytes long.
True
The TCP sliding window is used to implement flow control .
True
For a 10Mbps link, 100 bit times is 0.1ms.
False
Given the following received byte on an even-parity machine, there is definitely at least one error. 01001101
False
IP datagrams fragments can not be fragmented again.
False
If an IP datagram is fragmented into 1000-byte fragments, and later encounters a link with an 800-byte MTU, it is dropped.
False
In a fragmented IP datagram, the "offset" IP header field value is exactly equal to the number of bytes of fragmented data preceding this fragment.
False
It is fairly easy to detect collisions in wireless networks.
False
It is the responsibility of a routing algorithm to forward packets to the appropriate output link.
False
MAC addresses are redundant because of IP addresses.
False
Network address translation alters IP to add new IP addresses.
False
Star Ethernet uses the same multiple access control as Bus Ethernet.
False
The "Hop Limit" IPv6 header field indicates how many remaining hops to the destination.
False
The "traceroute" application (on Windows) sends UDP messages by default.
False
The IP header is encapsulated in IP datagram fragments
False
The IP header is encapsulated in IP datagram fragments.
False
The Internet Protocol (IP) header may be 21 bytes long.
False
The Internet Protocol (IP) implements congestion control.
False
The Internet Protocol (IP) implements data reliability services.
False
The Internet Protocol (IP) implements flow control.
False
The transport-layer header is encapsulated in every IP datagram fragment.
False
UDP has a congestion control mechanism.
False
UDP implements network fairness.
False
UDP uses an additive-increase multiplicative-decrease (AIMD) system to manage flows.
False
When sending a message to all devices on a link, you would send it to the broadcast MAC address: 00-00-00-00-00-00
False
he path MTU is the largest MTU on a path from sender to receiver.
False
1234::a03::abcd is a valid preferred-format IPv6 address.
False (can only represent zeros with "::" one time)
1234:0a03::abcd is a valid preferred-format IPv6 address.
False (why???)
::ffff:ffff:fffff is a valid preferred-format IPv6 host address.
False (why???)
Select all features explicit in IPv6 which are not explicitly available in IPv4.
Flow Labeling Payload Length 128-bit Addresses Extension Headers
There are reserved MAC addresses unusable for devices.
True
Convert the following IPv4 address to its corresponding IPv6-mapped address, with proper formatting. 114.18.222.10
::ffff:7212:de0a or ::ffff:114.18.222.10
What are some causes of network congestion? (Check all that apply)
Parallel TCP Connections. Reliable Data Transfer schemes. High utilization. Dropped TCP Packets. Typical Internet Usage.
The largest amount of data, in bytes, which can be accommodated throughout a datagram's route from sender to receiver is called the [a].
Path Maximum Transmission Unit (Path MTU)
Which of the following are used in a wireless network such as 802.11n?
Reservation system with Request to Send (RTS) and Clear to Send (CTS) Carrier Sense Multiple Access Exponential back-off/retry for collision resolution Collision Avoidance
The data-link layer provides logical communications between _____________________.
adjacent node and adjacent node
In host-inferred congestion control, congestion is detected based on delayed and/or dropped packets.
host-inferred
A MAC address was originally designed to be permanent and unique.
True
Ethernet provides ______________.
error detection via CRC check
Ethernet provides...
error detection via CRC check
A multiple access scheme which uses a master node to poll each slave node, and control who has 'permission' to transmit at any given time is called...
"taking turns" protocol
A host starts a TCP transmission with an EstimatedRTT of 48.1ms (from the "handshake"). The host then sends 3 packets and records the RTT for each: SampleRTT1 = 47.1 ms SampleRTT2 = 24.4 ms SampleRTT3 = 14.9 ms (NOTE: SampleRTT1 is the "oldest"; SampleRTT3 is the most recent.) Using an exponential weighted moving average with a weight of 0.4 given to the most recent sample, what is the EstimatedRTT for packet #4? Give answer in miliseconds, rounded to one decimal place, without units, so for an answer of 0.01146 seconds, you would enter "11.5" without the quotes.
(1-.4)(48.1) + (.4)(47.1ms) = 47.7 (1-.4)(47.7) + (.4)(24.4ms) = 38.38 (1-.4)(38.38) + (.4)(14.9ms) = 28.988
Given a 3 Gbps link with TCP applications A, B, and C. Application A has 25 TCP connections to a remote web server Application B has 2 TCP connection to a mail server Application C has 19 TCP connections to a remote web server. According to TCP "fairness", during times when all connections are transmitting, how much bandwidth should Application C have? (Give answer in Mbps, rounded to one decimal place, without units. So for an answer of 1234,567,890 bps you would enter "1234.6" without the quotes.)
(19 / 25+2+19) * 3 Gbps = 1,239.1 Mbps
Given a nodal delay of 68ms when there is no traffic on the network (i.e. usage = 0%), what is the effective delay when network usage = 31.5% ? (Give answer is milliseconds, rounded to one decimal place, without units. So for an answer of 0.10423 seconds you would enter "104.2" without the quotes).
(nodal delay) / (1 - network usage) = Effective Delay (68) / (1 - .315) = 99.3
For the following dotted-decimal IP address, give the binary representation: 10.108.112.240
00001010 01101100 01110000 11110000
Given the following "byte stuffing" scheme: Note: soh and eot are the framing characters. DATA: 79h 01h 78h 1Bh If byte stuffing is used to transmit Data, what is the byte sequence of the frame (including framing characters)? Format answer with capital hex values, with each value followed by an 'h' and separated by spaces, for example: 0Ah 12h
01h 79h 1Bh 78h 78h 1Bh 7Ah 04h (see picture)
What is the minimum UDP header size?
8 bytes
Put the following steps in the correct order for new host "Jetpack" joining a network with a DHCP-enabled server "Rhino". 1. ______ sends ______ to _______ 2. _______sends ________ to ________ 3. _______sends _______ to ______ 4. _____ sends ______ to _____
1. Jetpack, DHCP discover, MAC broadcast address 2. Rhino, DHCP offer, Jetpack's MAC address 3. Jetpack, DHCP request, MAC broadcast address 4. Rhino, DHCP acknowledgement, Jetpack's MAC address
For the following binary IP address, give the dotted-decimal representation: 11111000 00011111 11000111 11111000
248.31.199.248
What is the longest-common-prefix for the following address range? 10011110 10111001 10011101 00000000 -- 10011110 10111001 10011101 10000000
10011110 10111001 10011101
Assume a TCP sender is continuously sending 1,096-byte segments. If a TCP receiver advertises a window size of 8,551 bytes, and with a link transmission rate 35 Mbps an end-to-end propagation delay of 33.3 ms, what is the utilization? Assume no errors, no processing or queueing delay, and ACKs transmit instantly. Also assume the sender will not transmit a non-full segment. Give answer in percentages, rounded to one decimal place, without units (e.g. for an answer of 10.43% you would enter "10.4" without the quotes).
2.6
HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #4,063. HostA now sends segments of the same application data stream in order: P: 135 bytesQ: 273 bytesR: 284 bytes What is the sequence number on segment P?
4064
HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #3,264. HostA now sends segments of the same application data stream in order: P: 428 bytesQ: 226 bytesR: 346 bytes Suppose the segments arrive at Host B in the order Q, P, and R. What is the acknowledgment number on the segment sent in response to segment R?
4265
HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #4,345. HostA now sends segments of the same application data stream in order: P: 305 bytesQ: 493 bytesR: 110 bytes Suppose segments P, Q, and R arrive at Host B in order. What is the acknowledgment number on the segment sent in response to segment Q?
5,144
HostA has established a TCP connection with HostB in a remote network. HostA is sending packets to HostB. Assume we have configured TCP, somehow, to ACK every segment (no ACKing every other segment). Assume that the timeout is the same for all packets. HostB's "window size" is 20000 bytes. HostB has already received and acknowledged everything sent by HostA's application up to and including byte #4,891. HostA now sends segments of the same application data stream in order: P: 230 bytesQ: 465 bytesR: 294 bytes Suppose the segments arrive at Host B in the order Q, P, and R. What is the acknowledgment number on the segment sent in response to segment R?
5,881
Given an effective delay of 51ms when network usage is 60%, what is the effective delay when network usage = 10% ? (Give answer is milliseconds, rounded to one decimal place, without units. So for an answer of 0.10423 seconds you would enter "104.2" without the quotes).
51 = (x) / (1 - .6) x = 20.4 effective delay = 20.4 / (1 - .1) effective delay = 22.7
Select words/phrases from the dropdown menus to define the process of sending a message from host A to host D in the diagram below. Each phrase may be used zero or more times. Subnet #1 has the network address 198.137.25.0 / 24. Host A, Host B, and NIC #1 of Router A are connected to Subnet #1. Host A: 198.137.25.2 and 22:33:44:55:66:77 Host B: 198.137.25.3 and 33:44:55:66:77:88 Subnet #2 has the network address 223.87.156.0 / 24. Host C, Host D, NIC #2 of Router A, and NIC #3 of Router B are connected to Subnet #2. Host C: 223.87.156.3 and 66:77:88:99:AA:BB Host D: 223.87.156.4 and 77:88:99:AA:BB:CC __________________________________________ A finds that D belongs to a different subnet by checking ___________ . A looks up ______________ in its routing table. A uses ARP to get __________ . A creates frame with __________ as destination. Frame contains IP datagram with ________ as destination. A's NIC sends frame and RouterA's NIC receives it. RouterA removes IP datagram from frame, learns that its destination is _______________ . RouterA uses ARP to get ____________ . RouterA creates frame with ___________ as destination. Frame contains IP datagram with ______________ as destination. RouterA's NIC sends frame and D's NIC receives it.
A finds that D belongs to a different subnet by checking (D's IP address) . A looks up (RouterA's NIC#1 IP address) in its routing table. A uses ARP to get (RouterA's NIC#1 MAC address) . A creates frame with (RouterA's NIC#1 MAC address) as destination. Frame contains IP datagram with (D's IP address) as destination. A's NIC sends frame and RouterA's NIC receives it. RouterA removes IP datagram from frame, learns that its destination is (D's IP address) . RouterA uses ARP to get (D's MAC address) . RouterA creates frame with (D's MAC address) as destination. Frame contains IP datagram with (D's IP address) as destination. RouterA's NIC sends frame and D's NIC receives it.
Select all Random Access schemes below.
ALOHA CSMA
The address table shown below would be maintained by a host, router, or switch by... Hardware address to IP address table Hardware Address IP Address 00-13-72-BA-C0-2310.0.1.142 00-13-72-BA-9E-F010.0.2.5 00-13-72-BA-33-7A10.0.3.213
ARP
To retrieve an adjacent node's MAC address, ______ is used.
ARP
Which of the following are used in a wired Ethernet network? (Check all that apply)
Collision Detection (CD) Exponential back-off/retry for collision resolution Carrier Sense Multi-Access (CSMA)
Select the appropriate new CongWin sizes for the following TCP Reno congestion scenario. Assume ssthresh is initially set to 8 MSS: Connection Established with new server host. CongWin = ACK(s) received from first segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = Triple Duplicate ACK occurs. CongWin = ACK(s) received from next segment set. CongWin =
Connection Established with new server host. CongWin = 1 ACK(s) received from first segment set. CongWin = 2 ACK(s) received from next segment set. CongWin = 4 ACK(s) received from next segment set. CongWin = 8 ACK(s) received from next segment set. CongWin = 9 ACK(s) received from next segment set. CongWin = 10 ***NOTE: in the case of Triple Duplicate Acks:*** ***ssthresh = (congestion window) / 2*** ***congestion window = ssthresh + 3 * MSS*** Triple Duplicate ACK occurs. CongWin = 8 ssthresh = 5 ACK(s) received from next segment set. CongWin = 9
Select the appropriate new CongWin sizes for the following TCP Reno congestion scenario. Assume ssthresh is initially set to 8 MSS: Connection Established with new server host. CongWin = ACK(s) received from first segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = ACK(s) received from next segment set. CongWin = Timeout occurs. CongWin = ssthresh = ACK(s) received from next segment set. CongWin =
Connection Established with new server host. CongWin = 1 ACK(s) received from first segment set. CongWin = 2 ACK(s) received from next segment set. CongWin = 4 ACK(s) received from next segment set. CongWin = 8 ACK(s) received from next segment set. CongWin = 9 ACK(s) received from next segment set. CongWin = 10 Timeout occurs. CongWin = 1 ssthresh = 5 ACK(s) received from next segment set. CongWin = 2
Match the event with the TCP receiver action:
Delayed ACK. Wait up to 500ms for arrival of another in-order segment. If next in-order segment does not arrive in this interval, send an ACK.
Select the proper equation for TCP's calculation of DevRTT.
DevRTTn = (1 - B)*DevRTTn-1 + B*SampleRTTnew - EstimatedRTTn-1
What are some possible consequences of network-core congestion? (Check all that apply)
Dropped Packets Delayed packets Increased network congestion Out-of-order packet arrival Network collapse
The rate of CongWin size increase (in terms of MSS) while in TCP's Slow-Start phase is Exponential .
Exponential
The rate of CongWin size increase (in terms of MSS) while in TCP's Slow-Start phase is ______________
Exponential
Select all Channel Partitioning schemes below.
FDMA TDMA
A MAC address is permanent and unique.
False
A switch is a network-layer device.
False
Which of the following are benefits of a virtual circuit network? (Check all that apply)
Guaranteed bandwidth. Guaranteed timing. Connection states are preserved.
For a TCP/IP datagram coming into a home network through a NAPT device, which of the following header fields (IP and/or TCP) are altered? (Check all that apply)
Header Checksum Destination IP address Destination Port
Select all features explicitly available in IPv6 which were already available explicitly in IPv4.
Hop Limit Version Source/Destination Addressing Traffic Type
Which of the following are major issues that must be handled in wireless networks (i.e., issues that are more significant than in wired networks). Check all that apply.
Hosts may frequently move from one network to another Obstacles that block radio signals The "hidden node" problem Radio waves are more susceptible to interference than signals carried on cable Multi-path propagation when radio signals bounce off obstacles
Suppose that a 2200-byte datagram (identification #40) must transit a network which has a 660-byte MTU. Assume the minimum IP and TCP header sizes, i.e., the IP header is 20 bytes and the TCP header is 20 bytes. How many fragments are created? How many bytes of application data are carried in the first fragment? How many bytes of application data are carried in the second fragment? How many bytes of application data are carried in the last fragment? What is the identification number of the second fragment? # What is the fragment offset in the last fragment?
How many fragments are created? 4 How many bytes of application data are carried in the first fragment? 620 How many bytes of application data are carried in the second fragment? 640 How many bytes of application data are carried in the last fragment? 260 What is the identification number of the second fragment? # 40 What is the fragment offset in the last fragment? 240
In a prefix-matching network, a routing table stores... (Check all that apply)
IP Prefixes Next-Hop link information
Arrival of segment that partially or completely fills in gap in received data.
Immediately send ACK, provided that segment starts at the lower end of gap.
Arrival of out-of-order segment with higher-than-expected sequence number.
Immediately send duplicate ACK, indicating sequence number of next expected byte.
Which of the following are benefits of a datagram network? (Check all that apply)
Less overhead than a VC network. Faster delivery.
Imagine a mythical set of protocols with the following details. Maximum Link-Layer data frame: 852 bytes Network-Layer header size: 19 bytes Transport-Layer header size: 30 bytes What is the size, in bytes, of the MSS? (Give answer without units)
MSS = Link - Network - Transport MSS = 852 - 19 - 30 = 803
A device which moves between networks is a ______ device.
Mobile
For the IPv4 CIDR address 153.10.22.56 /22 What is the... Netmask: Network Address: Host Mask: Broadcast Address: Number of possible hosts: Host Number:
Netmask: 255.255.252.0 Network Address: 153.10.20.0 Host Mask: 0.0.3.255 Broadcast Address: 153.10.23.255 Number of possible hosts: 1022 Host Number: 568
What can cause queueing at a router's input ports? (Check all that apply)
Output port contention. Head of Line blocking. Slow outbound link transmission rate.
A private network uses a NAPT device at public IP address 53.54.56.200 The computers in the network use addresses of the form 10.0.0.x/22. Suppose that computer inside the NATed network sends a request with Source address: 10.0.0.100Source port: 992 Destination address: 101.5.32.130Destination port: 25 The next available port number on the NAPT device is 10639. PART 1: What source and destination information do the request packet headers contain when the request is sent out by the sending host? PART 1: What source and destination information do the request packet headers contain when the request is sent out by the sending host? Source address: Source port : Destination address: Destination port : PART 2: What source and destination information do the request packet headers contain when the request is sent out by the NAT box? Source address: Source port : Destination address: Destination port : PART 3: What source and destination information do the response packet headers contain when the response is received by the NAT box? Source address: Source port : Destination address: Destination port : PART 4: What source and destination information do the response packet headers contain when the response is received by the original sending host? Source address: Source port : Destination address: Destination port :
PART 1: What source and destination information do the request packet headers contain when the request is sent out by the sending host? PART 1: What source and destination information do the request packet headers contain when the request is sent out by the sending host? Source address: 10.0.0.100 Source port : 992 Destination address: 101.5.32.130 Destination port : 25 PART 2: What source and destination information do the request packet headers contain when the request is sent out by the NAT box? Source address: 53.54.56.200 Source port : 10639 Destination address: 101.5.32.130 Destination port : 25 PART 3: What source and destination information do the response packet headers contain when the response is received by the NAT box? Source address: 101.5.32.130 Source port : 25 Destination address: 53.54.56.200 Destination port : 10639 PART 4: What source and destination information do the response packet headers contain when the response is received by the original sending host? Source address: 101.5.32.130 Source port : 25 Destination address: 10.0.127.100 Destination port : 992
Select all "Taking Turns" schemes below.
Polling Multiple Access Token Ring Multiple Access
Upon encountering a router with the following routing table: 0: 10011110 00011110 10001111 1: 10011110 00011110 10001111 000 2: 10011110 00011110 10001111 01 3: 10011110 00011110 10001110 0001 4: default A datagram with the destination IP address 158.30.143.10 would be routed to
Port 1
ICMP can carry messages from... (Check all that apply)
Router to Sender Host Destination Host to Source Host Source Host to Destination Host Router to Router
S represents a source host and D represents a destination host. Which of the following is the most typical use of public key encryption, when S sends an encrypted message to D?
S encrypts a message using D's public key, and D decrypts the message using D's private key.
S represents a source host and D represents a destination host. Which of the following is the most typical use of public key encryption, when S sends an authenticated (digitally signed) message to D?
S encrypts a signature using S's private key, and D decrypts the signature using S's public key.
A __________________ -type retransmission protocol will retransmit one segment at a time upon a countdown timer interrupt.
Selective Repeat
In network graph terminology, a [a] from A to B is the set of edges to traverse to reach B from A for the lowest total cost.
Shortest Path
In a link between Host A, and Host B, we have three intermediary routers: Host A ----- Router Snucky ------ Router Jumpy ------ Router Po ------- Host B Host A's first hop router is Router Snucky .
Snucky
For a TCP/IP datagram leaving a home network through a NAPT device, which of the following header fields (IP and/or TCP) are altered? (Check all that apply)
Source IP Address Header Checksum Source Port
If an Ethernet sender senses a clear channel, and begins transmission, but shortly thereafter detects a collision, it will...
Terminate transmission and enter exponential backoff.
In direct routing, after the initial contact with the home network, the correspondent sends packets to
The care-of address
A TCP fast-retransmit will occur after...
Three duplicate ACKS for the same segment.
If hosting a server inside a NATed network, how do clients outside the NAPT router connect to the server? (Check all that apply)
Using Universal Plug and Play (UPnP) By using the NAPT devices IP address, and a port number pre-configured to correspond to the server. Through a connection relay service
Which of the following are fields in the TCP header? (Select all that apply)
Window Size Checksum Correct! Sequence Number Header Length/Data Offset Correct! Destination Port Correct! Source Port
In one type of wireless network, hosts communicate directly with other hosts that are within range. This communication model forms a "grid" called a(n)
ad-hoc network
A link-layer link between more than two adjacent nodes is called a/an broadcast link.
broadcast
A network with a ___________ topology must terminate the endpoints, but in with a ___________ topology they are connected so there is no endpoint.
bus ring
A multiple access scheme which divides the usable medium into "chunks" and allows each device sole access to some number of "chunks" is called...
channel partitioning protocol
The TCP three-way handshake is used to implement a ________________ .
connection
Given an encryption scheme that uses encrypt(m) to encrypt message m, and uses decrypt(c) to get back the original message. (m is the original message, and c is the encrypted message.) Which of the following must be true?
decrypt(encrypt(m)) = m
When encountering an IPv4-only router, an IPv6 datagram is _____________ an IPv4 datagram, with the _______________ as its destination.
encapsulated in next in-line IPv6 router
When encountering an IPv4-only router, an IPv6 datagram is an IPv4 _____________ datagram, with the __________________ as its destination.
encapsulated in next in-line IPv6 router
Retransmitting a missing segment before the segment's countdown timer expires is called...
fast retransmission
In IPv6, datagram fragmentation is _________________ .
handled at the network edge
Given an internet represented as a weighted undirected graph, the shortest path between node X and node Y is the path that...
has the smallest sum of edge weights.
The network layer manages communications from _____ to _______.
host to host
A protocol designed to control access to a medium is most commonly called a
multiple access protocol
In network-assisted congestion control, flags may be set during transit which indicate the presence and/or level of congestion in certain portions of the network.
network-assisted
An organization typically implements its firewall security by using
packet filtering
A link-layer link between only two adjacent nodes is called a/an ____________ link.
point to point
A link-layer link between only two adjacent nodes is called a/an ____________.
point to point link
The process of determining a path through the internet is called _____________.
routing
A router's routing table is output by a ________________________.
routing algorithm
The process of determining a path through the internet is handled by the _________________.
routing algorithm
Most modern Ethernet LANs use a _____ topology.
star
A group of hosts sharing a common address prefix, behind a router, is called a/an _____________.
subnet
In a subnet, the reserved addresses are the ________________ and the ______________.
subnet address broadcast address
The link-layer device at the center of an ethernet star is a ______________.
switch
In addition to a "default" entry, routing tables in an internet store...
the "first hop" in a path to each of the networks known to the router
Re-assembly of fragmented IP datagrams is handled by...
the destination host.
On the sending or receiving host, most of the protocol tasks "below" the application layer of the protocol stack (data encapsulation, IP addressing, etc. ) are handled by
the network interface controller (NIC)
The "time to live" field in a modern IPv4 datagram header specifies...
the number of remaining hops before the datagram is dropped.
In a CSMA/CD system, when a collision is detected, ...
the sender will cut off transmission and wait some time before retransmitting.