430 Quiz 4

"In destination-based forwarding, ..."

. after matching on the destination IP address in the datagram header, the action taken is to forward the datagram to the output port associated with that destination IP address.

Which of the following statements about pipelining are true? One or more statements may be true.

1. A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver. 2. With a pipelined sender, there may be transmitted packets "in flight" - propagating through the channel - packets that the sender has sent but that the receiver has not yet received

What are some reasons for discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.

1. The sender will resend that packet in any case 2. The implementation at the receiver is simpler.

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

Which of the following addresses can not be used by an interface in the 223.1.3/29

223.1.3.16 223.1.2.6 223.1.3.28

What is the maximum # of interfaces in the 223.1.2/24 network

256 because 32-24 = 8 and 2^8 = 256

reason for cutting window in half?

3 dup acks received (cut in half)

What is the maximum # of interfaces in the 223.1.3/29 network?

8, because 32-29 = 3, and 2^3 = 8 possible interfaces

Which of the following statements about a DHCP request message are true (check all that are true

A DHCP request message is sent broadcast, using the 255.255.255.255 IP destination address. A DHCP request message may contain the IP address that the client will use. The transaction ID in a DHCP request message will be used to associate this message with future DHCP messages sent from, or to, this client.

What is meant by a cumulative acknowledgment, ACK(n)

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

TCP segment format 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 field

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

ACK number field

Reliable data transfer protocol mechanisms. Lets the sender know that a packet was received correctly at the receiver.

ACK numbers

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.

Consider the TCP Telnet scenario below. Why is it that the receiver sends an ACK that is one larger than the sequence number in the received datagram?

Because the send-to receiver segment carries only one byte of data, and after that segment is received, the next expected byte of data is just the next byte (i.e., has an index that is one larger) in the data stream.

Consider the TCP Telnet scenario below. What timer-related action does the sender take on the receipt of ACK 120?

Cancels any running timers

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

Checksum

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

Data(Payload)

Formula for DevRTT

DevRTT = 1-b DevRTT0 + b (srtt1 - ertt1)

formula for ERTT1

ERTT1 = (1-a) (ERTT0) + a SRTT

What are some reasons for not discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.

Even though that packet will be retransmitted, its next retransmission could be corrupted, so don't discard a perfectly well-received packet, silly!

Which of the following match+actions can be taken in the generalized OpenFlow 1.0 match+action paradigm

Everything except forwarding/dropping based on URL

True or False: On the sending side, the TCP sender will take each application-layer chunk of data written into a TCP socket and send it in a distinct TCP segment. And then on the receiving side, TCP will deliver a segment's payload into the appropriate socket, preserving the application-defined message boundary.

FALSE: There is no notion of message boundaries in TCP's byte-stream view of the world. This contrasts with UDP, which does preserves application-defined message boundaries.

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

FIN message

TCP connection management 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.

Which of the following network devices can be thought of as a "middlebox"

HTTP load balancer HTTP cache Network address translation box

TCP segment format This field contains the number of bytes in the TCP header.

Header length field

What fields can be matched in generalized match+action.

IP source address IP destination address Upper layer protocol field Source and/or destination port number IP TYPE OF SERVICE FIELD

What are the principal components of the IPv4 protocol

IPv4 datagram format. IPv4 addressing conventions. Packet handling conventions at routers (e.g., segmentation/reassembly)

Reliable data transfer protocol mechanisms. 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.

TCP connection management 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

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

Receiver advertised window

Reliable data transfer protocol mechanisms. Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission.

Retransmission

Consider the rdt 2.0 sender and receiver shown below, with FSM transitions at the sender labeled S1, S2, and S3; and receiver transitions labeled R1 and R2.Which of the following sequences of transitions could possibly occur as a result of an initial rdt_send() call at the sender, and possible later message corruption and subsequent error recovery.

S1, R2, S3 S1, R1, S2 S1, R1, S2, R2,S3

TCP connection management A message from client to server initiating a connection request

SYN message

TCP connection management 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

TCP segment format 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

TCP segment format. This field contains the source port number associated with the sending socket for this TCP segment

Source port number

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

IPV4 header Time-to-live field

The value of this field is decremented at each router, when it reaches 0, the packet is dropped

IPV4 header Type-of-service field

This field contains the ECN and differentiated service bits

IPV4 header Header checksum field

This field contains the internet checksum of the packet's header fields

IPV4 header Fragmentation offset field

This field is used for datagram fragmentation and reassembly

What is the purpose of the Dynamic Host Configuration Protocol?

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

Reliable data transfer protocol mechanisms. Used by sender or receiver to detect bits flipped during a packet's transmission.

checksum

IPV4 header datagram length field

indicates the total number of bytes in the datagram

Reliable data transfer protocol mechanisms. allows for duplicate detection at receiver

sequence numbers

IPV4 header payload/data field

this field contains a TCP or UDP segment, for example

IPV4 header Version field?

this field contains the ip protocol version number

IPV4 header Upper layer field

this field contains the protocol number to which the datagram's payload will be demultiplexed. UDP or TCP

Formula for Timeout interval

timeout interval = estimatedRTT + 4*devRTT

reason to drop throughput to 1?

timeout occurred