Ccna certification Practice Tests

271

 97.  A.  When a programmer decides to use UDP, it is normally because the programmer is 

sequencing and acknowledging datagrams already. The redundancy of acknowledgments 

at the Transport layer is not needed. Guaranteed delivery of segments is not a function 

of UDP. UDP does not provide windowing flow control because acknowledgment is not 

a function of UDP. A virtual circuit can only be created with a setup and teardown of 

communications, such as TCP offers.

 98.  B.  When a daemon or server process starts, it binds to a port number on which to listen 

for a request. An example is a web server binding to the port number of TCP/80. A port 

is communicated in the header of TCP and UDP segments, but the header does not listen 

for requests or bind. MAC addresses are physical locations on a local area network (LAN) 

that are used to transmit framed data. Checksums are used to verify that data are not 

erroneously modified in transit.

 99.  A.  The window size, which is a buffer, is established and agreed upon by the sender and 

receiver during the three-way handshake. Sliding windows does not allow for data of 

different lengths to be padded; it is used for fixed-length data segments. Port binding is 

used by TCP and UDP to indicate which upper-layer protocol (application) created the 

request. Routers only examine layer 3 information by default, so they can make decisive 

routing decisions.

 100.  C.  DNS requests are usually small and do not require the overhead of sequence and 

acknowledgment of TCP. If a segment is dropped, the DNS protocol will ask again. 

Acknowledgment of data is not a function of UDP. Flow control is not a function of UDP 

since UDP does not offer flow control of data other than a stop/go action. UDP does not 

build temporary virtual circuits; this is a function of TCP.

 101.  A.  A three-way handshake is required between sender and receiver before TCP can 

begin sending traffic. During this three-way handshake, the sender’s window buffer 

size is synchronized with the receiver’s window buffer size. Ports are not agreed upon; 

they are used for the addressing of traffic at the Transport layer. The sequencing and 

acknowledgment of segments is a function of the TCP protocol.