Explanation

Packet Filtering Firewall - only examines an IP packet based on Source IP (SIP),
Destination IP (DIP), Source Port and Destination Port for both UDP and TCP by subjecting each
IP packet to an Access Control List.

The other answers are incorrect
The following reference(s) were/was used to create this question:
http://www.portknocking.org/

802.3 uses a Length field which indicates the number of data
bytes that are in the data field. Ethernet II uses a Type field in the
same 2 bytes to identify the message protocol type. Both frame formats
use a 8-byte Preamble field at the start of the packet, and a 4-
byte Frame Check Sequence (FCS) field at the end of the packet, so

image004
those choices would be incorrect as to a difference in the frame formats.
Sources: Gigabit Ethernet by Jayant Kadambi, Ian Crayford, and
Mohan Kalkunte (Prentice Hall PTR, 1998) and CCNA Study Guide by
Todd Lammle, Donald Porter, and James Chellis (Sybex, 1999).

War dialing, or scanning, has been a common activity in the computer underground and computer security industry for decades. Hollywood made war dialing popular with the 1983 movie, War Games, in which a teenager searching for a videogame company ultimately uncovers a government nuclear war warning system. The act of war dialing is extremely simple - a host computer dials a given range of telephone numbers using a modem. Every telephone number that answers with a modem and successfully connects to the host is stored in a log. Disabling call forwarding is not a useful countermeasure because it's the attacker machine the one who connects to the attacked system and forwarding is not an issue inside the attack. Answer A, C and D can be used as countermeasures to harder the war dial attack.