Networks Final

Which of the following statements about pipelining are true?

-A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver -With a pipelined sender, there may be transmitted packets "in flight" - propagating through the channel - packets that the sender has sent but the receiver has not yet received

What is meant by an IP subnet?

-A set of device interfaces that can physically reach each other without passing through an intervening router -A set of devices that have a common set of leading high order bits in their IP address

Which of the following statements is true regarding an IP address?

-An IP address is associated with an interface -If a host has more than one interface, then it has more that one IP address at which it can be reached -If a router has more than one interface, then it has more that one IP address at which it can be reached

What are advantages of implementing transport-layer functionality in QUIC at the application layer? Select all that apply.

-As an application-layer protocol, QUIC can be updated/modified at "app frequency" rather than at the frequency of operating system updates -QUIC can establish all connection parameters (security, reliability, flow and congestion control)in just one handshake rather than separately in two

Which of the following statements correctly identify the differences between routing and forwarding. Select one or more statements.

-Forwarding refers to moving packets from a router's input to appropriate router output, and is implemented in the data plane -Routing refers to determining the route taken by packets from source to destination, and is implemented in the control plane

Which of the following fields occur ONLY in the IPv6 datagram header (i.e., appear in the IPv6 header but not in the IPv4 header)?

-128-bit source and destination IP addresses -The flow label field

Consider Dijkstra's link-state routing algorithm that is computing a least-cost path from node a to other nodes b, c, d, e, f. Which of the following statements is true.

-In the initialization step, the initial cost from a to each of these destinations is initialized to either the cost of a link directly connecting a to a direct neighbor, or infinity otherwise -Suppose nodes b, c, and d are in the set N'. These nodes will remain in N' for the rest of the algorithm, since the least-cost paths from a to b, c, and d are known -The values computed in the vector D(v), the currently known least cost of a path from a to any node v, will never increase following an iteration

Which of the fields below are in a UDP segment header?

-Internet checksum -Source port number -Destination port number -Length (of UDP header plus payload)

For each of the actions below, select those actions below that are primarily in the network-layer data plane. The other actions that you don't select below then correspond to control-plane actions

-Looking up address bits in an arriving datagram header in the forwarding table -Moving an arriving datagram from a router's input port to output port -Dropping a datagram due to a congested (full) output buffer

Which of the following network devices can be thought of as a "middlebox"? Check all that apply.

-Network Address Translation box -HTTP load balancer -HTTP cache

Check all of the services below that are provided by the TCP protocol

-Reliable data delivery -In-order data delivery -A congestion control service to ensure that multiple senders do not overload network links -A flow-control service that ensures that a sender will not send at such a high rate so to overflow the receiving host buffers -A byte stream abstraction, that does not perserve boundaries between message data sent in different socket send calls at the sender

Check all of the statements below about where (in the network) the network layer is implemented that are true

-The network layer is implemented in hosts at the network's edge -The network layer is implemented in routers in the network core

What is meant by a cumulative acknowledgement, ACK(n)?

A cumulative ACK(n) acks all packets with a sequence number up to and including n as being received

Lets the sender know that a packet was received correctly at the receiver

ACK

If set, this segment cumulatively ACKs all data bytes up to, but not including, the byte index in the ACK value field of this segment

ACK bit

This field contains the index in the byte stream of the next in-order byte expected at the receiver

ACK number field

How is the sending rate typically regulated in a TCP implementation?

By keeping a window of size cwnd over the sequence number space, and making sure that no more than cwnd bytes of data are outstanding (i.e, unACKnowledged). The size of cwnd is regulated by AIMD.

This field contains the Internet checksum of the TCP segment and the selected fields in the IP datagram header

Checksum

Used by sender or receiver to detect bits flipped during a packet's transmission

Checksum

The transport layer sits on top of the network layer, and provides its services using the services provided to it by the network layer. Thus it's important that we know what is meant by the network layer's "best effort" delivery service. True or False: The network layer's best-effort delivery service means that IP makes its "best effort" to deliver segments between communicating hosts, but it makes no guarantees. In particular, it does not guarantee segment delivery, it does not guarantee orderly delivery of segments, and it does not guarantee the integrity of the data in the segments.

Correct

This field contains application data that was written into a socket by the sender of this TCP segment

Data (or payload)

A message indicating that the sending side is initiating the protocol to terminate a connection

FIN message

A message sent in response to a request to terminate a connection, ACKing that the side receiving this message is also willing to terminate the connection

FINACK message

Which one of the following operations is not performed by NAT.?

Generating ACKs back to the TCP sender and then taking responsibility for reliably delivery the segment to its destination, possibly using a non-TCP reliable data transfer protocol.

This field contains the number of bytes in the TCP header

Header length field

What protocol (or protocols) constitutes the "thin waist" of the Internet protocol stack?

IP

Lets the sender know that a packet was NOT received correctly at the receiver

NAK

What is meant by saying that DHCP is a "plug and play" protocol?

No manual configuration is needed for the host to join the network

Which of the following quality-of-service guarantees are part of the Internet's best-effort service model? Check all that apply.

None of the other services listed here are part of the best-effort service model. Evidently, best-effort service really means no guarantees at all!

How many RTTs are needed to establish an HTTP/3 connection (i.e., before data can begin to flow between client and server) using QUIC?

One RTT. Reliability, congestion control, flow control, and security parameters are established in the first two parts of the setup handshake, which takes one RTT

A general purpose error message used during connection set up or tear down to let the other side know that an error has occurred, and that the referenced connection should be shut down

RESET message

This field contains the number of available bytes in the TCP receiver's buffer

Receiver advertised window

What is meant by transport-layer demultiplexing?

Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket

Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission

Retransmission

What is the definition of a "good" path for a routing protocol?

Routing algorithms typically work with abstract link weights that could represent any of, or combinations of, all of the other answers

A message from client to server initiating a connection request

SYN message

A message from server to client ACKing receipt of a SYN message and indicating the willingness of the server to establish a TCP connection with the client

SYNACK message

This field contains the index in the sender-to-receiver byte stream of the first byte of that data in the payload carried in this segment

Sequence number

Allows for duplicate detection at receiver

Sequence numbers

The field contains the port number associated with the sending socket for this TCP segment

Source port number

What is meant by transport-layer multiplexing?

Taking data from one socket (one of possibly many sockets), encapsulating a data chunk with header information - thereby creating a transport layer segment - and eventually passing this segment to the network layer

What is the purpose of the Dynamic Host Configuration Protocol?

To obtain an IP address for a host attaching to an IP network

Where is the transport-layer functionality primarily implemented?

Transport layer functions are implemented primarily at the hosts at the "edge" of the network

True or False: with TCP's flow control mechanism, where the receiver tells the sender how much free buffer space it has (and the sender always limits the amount of outstanding, unACKed, in-flight data to less than this amount), it is not possible for the sender to send more data than the receiver has room to buffer.

True

True or False: It is possible for two TCP segments with source port 80 to be sent by the sending host to different clients.

True (because TCP demultiplexing happens on the basis of four values (source and destination port numbers, and IP addresses) rather than just on the basis of the destination port number, as is done for UDP)

True or False: When multiple UDP clients send UDP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host.

True (because UDP demultplexing happens solely on the basis of destination port number. Thus, segments with the same destination port number at a host will have their data demultiplexed to the same socket)

True or False: It is possible for two UDP segments to be sent from the same socket with source port 5723 at a server to two different clients.

True (because the application-layer program explicitly specifies the destination host IP address and port number when sending into a UDP socket, and that a single UDP socket (with a given source port number) can therefore be used to send to multiple UDP clients)

The sender measures RTTs and uses the current RTT measurement to infer the level of congestion

delay-based congestion control approach

The sender infers segment loss from the absence of an ACK from the receiver

end-end congestion control approach

Bits are set at a congested router in a sender-to-receiver datagram, and bits are in the returned to the sender in a receiver-to sender ACK, to indicate congestion to the sender

network-assisted congestion control approach