A security technician needs to open ports on a firewall to allow for domain name resolution.
Which of the following ports should be opened? (Select TWO).

A.
TCP 21
HTTP

B.
TCP 23
D: Telnet uses port 23.

Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, p. 51
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
QUESTION 143
A technician has just installed a new firewall onto the network. Users are reporting that they cannot reach
any website. Upon further investigation, the technician determines that websites can be reached by
entering their IP addresses. Which of the following ports may have been closed to cause this issue?
DHCP

C.
TCP 53
DNS

D.
UDP 23
NetBIOS

E.
UDP 53

B.
TCP 23
D: Telnet uses port 23.

Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, p. 51
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
QUESTION 143
A technician has just installed a new firewall onto the network. Users are reporting that they cannot reach
any website. Upon further investigation, the technician determines that websites can be reached by
entering their IP addresses. Which of the following ports may have been closed to cause this issue?
DHCP

A.
TCP 21
HTTP

B.
TCP 23
D: Telnet uses port 23.

Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, p. 51
http://en.wikipedia.org/wiki/List_of_TCP_and_UDP_port_numbers
QUESTION 143
A technician has just installed a new firewall onto the network. Users are reporting that they cannot reach
any website. Upon further investigation, the technician determines that websites can be reached by
entering their IP addresses. Which of the following ports may have been closed to cause this issue?
DHCP

C.
TCP 53
DNS

D.
UDP 23
NetBIOS

Explanation:
DNS uses TCP and UDP port 53. TCP port 53 is used for zone transfers, whereas UDP port 53 is used for
queries.Incorrect Answers:
A: FTP uses TCP port 21.

DNS links IP addresses and human-friendly fully qualified domain names (FQDNs), which are made up of
the Top-level domain (TLD), the registered domain name, and the Subdomain or hostname.
Therefore, if the DNS ports are blocked websites will not be reachable.
Incorrect Answers:A: HTTP is responsible for the transmission of HTML documents and embedded multimedia components.
B: Dynamic Host Configuration Protocol (DHCP) allows DHCP servers to assign, or lease, IP addresses to
computers and other devices that are enabled as DHCP clients.
D: NetBIOS is a program that allows applications on different computers to communicate within a local
area network (LAN).

Stewart, James Michael, CompTIA Security+ Review Guide, Sybex, Indianapolis, 2014, pp. 42, 46
https://technet.microsoft.com/en-us/library/cc896553(v=ws.10).aspx
http://en.wikipedia.org/wiki/NetBIOS