348 Appendix ■ Answers
3. C. Ben is using ad hoc mode, which directly connects two clients. It can be easy to
confuse this with stand-alone mode, which connects clients using a wireless access point
but not to wired resources like a central network. Infrastructure mode connects endpoints
to a central network, not directly to each other. Finally, wired extension mode uses a
wireless access point to link wireless clients to a wired network.- C. A collision domain is the set of systems that could cause a collision if they transmitted
at the same time. Systems outside a collision domain cannot cause a collision if they
send at the same time. This is important, as the number of systems in a collision domain
increases the likelihood of network congestion due to an increase in collisions. A broadcast
domain is the set of systems that can receive a broadcast from each other. A subnet is a
logical division of a network, while a supernet is made up of two or more networks. - D. The RST flag is used to reset or disconnect a session. It can be resumed by restarting
the connection via a new three-way handshake. - C. He should choose 802.11n, which supports 200+ Mbps in the 2.4 GHz or the 5 GHz
frequency range. 802.11a and 802.11ac are both 5 GHz only, while 802.11g is only
capable of 54 Mbps. - The TCP ports match with the protocols as follows:
- TCP port 23: D. Telnet.
- TCP port 25: A. SMTP.
- TCP port 143: C. IMAP.
- TCP port 515: B. LPD.
These common ports are important to know, although some of the protocols are be-
coming less common. SMTP is the Simple Mail Transfer Protocol, IMAP is the Internet
Message Access Protocol, and LPD is the Line Printer Daemon protocol used to send
print jobs to printers.
- A. The File Transfer Protocol (FTP) operates on TCP ports 20 and 21. UDP port 69 is
used for the Trivial File Transfer Protocol, or TFTP, while UDP port 21 is not used for any
common file transfer protocol. - B. Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum
(DSSS), and Orthogonal Frequency-Division Multiplexing (OFDM) all use spread
spectrum techniques to transmit on more than one frequency at the same time. Neither
FHSS nor DHSS uses orthogonal modulation, while multiplexing describes combining
multiple signals over a shared medium of any sort. WiFi may receive interference from
FHSS systems but doesn’t use it. - B. The Challenge-Handshake Authentication Protocol, or CHAP, is used by PPP servers
to authenticate remote clients. It encrypts both the username and password and performs
periodic reauthentication while connected using techniques to prevent replay attacks.
LEAP provides reauthentication but was designed for WEP, while PAP sends passwords
unencrypted. EAP is extensible and was used for PPP connections, but it doesn’t directly
address the listed items.