TCP/IP Questions and Answers

Answer: C

The resource record is TXT.

A TXT record associates arbitrary text with a domain name. It is widely used for machine-readable information as well, such as SPF records that list a domain's permitted mail servers and verification strings for web services.

An A record maps a host name to an IPv4 address. 'MCX' is not a record type (the mail record is MX), and 'Text' is not the name of the record type, which is written TXT.

Answer: C

TFTP uses fixed blocks of 512 bytes.

Trivial File Transfer Protocol (RFC 1350) sends data in numbered blocks of 512 bytes, each acknowledged before the next is sent. A block shorter than 512 bytes signals the end of the file.

Larger block sizes can be negotiated only through the later block-size option extension; the protocol's fixed block is 512, not 128, 256 or 1024.

Answer: A

The values are 86400 and 60 seconds.

In DNS resource records, the Time-to-live field says how long a cached record may be kept. Tanenbaum gives the example that highly stable information is assigned a large value such as 86400, the number of seconds in one day, and highly volatile information a small value such as 60, one minute.

The other pairs are not the textbook values; 36000 seconds is ten hours, and 0 would forbid caching altogether.

Answer: D

An A record gives the IP address of a host.

The A (address) resource record maps a host name to its 32-bit IPv4 address, which is the most common DNS lookup. AAAA records do the same for IPv6.

An NS record names an authoritative name server for a domain. A PTR (pointer) record maps an address back to a name, for reverse lookups. HINFO describes the host's CPU and operating system.

Answer: A

Emails are sent with SMTP.

The Simple Mail Transfer Protocol carries mail from the sender's client to its mail server and between mail servers, usually on port 25 between servers and 587 for client submission. Retrieving mail from a mailbox is done by different protocols, POP3 or IMAP.

HTTP transfers web pages (webmail uses it only between the browser and the webmail site), FTP transfers files, and Telnet gives an unencrypted remote terminal session.

Answer: C

The connection-oriented protocol is TCP.

The Transmission Control Protocol sets up a connection with a three-way handshake (SYN, SYN-ACK, ACK) before any data flows, and then provides reliable, ordered delivery with acknowledgements, retransmission and flow control, before closing the connection.

UDP sends independent datagrams with no handshake, and IP is a connectionless best-effort protocol. HTTP is an application-layer protocol that runs over TCP; the connection it uses is TCP's, so HTTP itself is not the connection-oriented protocol.

Answer: D

End-to-end connectivity is provided by the Transport layer.

The transport layer (layer 4) is the first truly end-to-end layer: its protocols, such as TCP and UDP, run only on the two communicating hosts, and it gives the source and destination a direct logical connection with segmentation, flow control and reliable delivery.

The network layer moves packets hop by hop through routers, and the data link layer works only across a single link. The session layer manages dialogues between applications on top of a connection the transport layer already provides.

Answer: D

RTSP is used for all of the mentioned purposes.

The Real Time Streaming Protocol is a network control protocol for streaming media servers. It establishes and controls media sessions between endpoints, and gives the client VCR-like commands such as PLAY, PAUSE and TEARDOWN for real-time control of playback from the server. The media itself is usually carried by RTP.

Each of the first three options describes one part of what RTSP does, so none is complete on its own.

Answer: C

The protocol for secure communication is HTTPS.

HTTPS is HTTP carried over TLS (formerly SSL), which encrypts the data between browser and server and authenticates the server with a certificate, protecting passwords and payments from eavesdropping.

Plain HTTP, FTP and SMTP send data unencrypted by default, so they are not secure protocols in themselves.

Browsers show a padlock in the address bar for HTTPS sites, and the protocol uses port 443 by default instead of HTTP's port 80.

Answer: C

An IP address is obtained from a DHCP server using DHCP.

The Dynamic Host Configuration Protocol assigns IP addresses automatically: the client broadcasts a Discover message, the server makes an Offer, the client Requests it and the server Acknowledges (the DORA exchange).

ARP maps an IP address to a MAC address, ICMP carries error and diagnostic messages such as ping, and DNS translates domain names into IP addresses.