〇：IP Session Restriction via Media Gateway

The VoIP Media Gateway translates Internet Protocol (VoIP) voice over time division multiplexing (TDM) voice to and from. As a security measure, the number of calls through the Media Gateway should be limited. The Media Gateway is vulnerable to denial-of-service attacks, hijacking, and other types of attacks.

×：Identification of Rogue Devices  

Incorrect, as rogue devices on both IP telephony and data networks need to be identified.

×：Implementation of Authentication

Incorrect because authentication is recommended for both data and voice networks.

×：Encryption of packets containing sensitive information

Incorrect because sensitive data can be transmitted over either voice or data networks and must be encrypted in both cases. Eavesdropping is a very real threat for VoIP networks.

IEEE 802.11 is one of the wireless LAN standards established by IEEE.

Diameter is an authentication protocol that implements the AAA (Authentication, Authorization, Accounting) service, the successor to RADIUS. This can cause performance degradation and data loss. This can lead to performance degradation and data loss.

〇：VLAN

Virtual LANs (VLANs) allow logical isolation and grouping of computers based on resource requirements, security, or business needs, despite the standard physical location of the system. Computers in the same department configured on the same VLAN network can all receive the same broadcast messages, allowing all users to access the same types of resources regardless of their physical location.

×：Open Network Architecture  

Open network architecture is wrong because it describes the technology that can configure a network; the OSI model provides a framework for developing products that operate within an open network architecture.

×：Intranet

Incorrect because an intranet is a private network used by a company when it wants to use Internet and Web-based technologies in its internal network.

×：VAN  

Incorrect because a Value Added Network (VAN) is an electronic data interchange (EDI) infrastructure developed and maintained by a service bureau.

A captive portal is a mechanism that restricts communication with the outside world until user authentication, user registration, and user consent are performed when a terminal connects to the network.

A well-known port is a port number from 0 to 1023 that is reserved for standard services. There are three port number combinations. Well-known port numbers (0-1023) are port numbers officially registered with IANA. Registered port numbers (1024-49151) are port numbers that are officially registered with IANA. A dynamic/private port number (49152-65535) is a port number that is not officially registered with IANA.

War Dialing is the indiscriminate and repeated act of cracking dial-ups in search of dial-up lines, such as those for non-public internal networks. It automatically scans a list of telephone numbers, usually dialing all numbers in the local area code, and searches modems, computers, bulletin board systems, and fax machines.

〇：DNSSEC

DNSSEC is a set of extensions to the DNS that provide DNS clients (resolvers) with authentication of the origin of DNS data to reduce the threat of DNS poisoning, spoofing, and similar attack types. It is an Internet Engineering Task Force (IETF) specification for securing services.

×：Resource Record

DNS servers contain records that map hostnames to IP addresses, called resource records. The answer is incorrect. When a user’s computer needs to resolve a hostname to an IP address, it looks in its network configuration to find its DNS server. The computer then sends a request containing the hostname to the DNS server for resolution; the DNS server looks at its resource records, finds a record with this particular hostname, retrieves the address, and responds to the computer with the corresponding IP address.

×：Zone Transfer

Primary and secondary DNS servers synchronize their information via zone transfers. The answer is incorrect. After changes are made to the primary DNS server, these changes must be replicated to the secondary DNS server. It is important to configure the DNS servers so that zone transfers can take place between specific servers.

×：Resource Transfer

Equivalent to transferring DNS resource records, but the answer is incorrect.

Application firewalls target Layer 7 of the OSI. The main advantage of an application firewall is its ability to understand specific applications and protocols. Packets are not decrypted until Layer 6, so Layer 7 can see the entire packet. Other firewalls can only inspect the packet, not the payload. It can detect if an unwanted application or service is trying to bypass the firewall by using a protocol on an allowed port, or if the protocol is being used in a malicious manner.

〇：DNS Hijacking

The DNS plays a great role in the transmission of traffic on the Internet; it directs traffic to the appropriate IP address corresponding to a given domain name DNS queries can be classified as either recursive or iterative. In a recursive query, the DNS server forwards the query to another server, which returns the appropriate response to the inquirer. In an iterative query, the DNS server responds with the address of another DNS server that may be able to answer the question and then proceeds to further ask for a new DNS server. Attackers use recursive queries to pollute the caches of DNS servers.

The attacker sends a recursive query to the victim’s DNS server asking for the IP address of the domain; the DNS server forwards the query to another DNS server. Before the other DNS server responds, the attacker inserts his IP address. The victim server receives the IP address and stores it in its cache for a specific period of time. The next time the system queries the server for resolution, the server directs the user to the attacker’s IP address.

×：Manipulating the hosts file

Manipulating the hosts file is wrong because it does not use recursive queries to pollute the DNS server cache. The client queries the hosts file before issuing a request to the first DNS server. Some viruses add the antivirus vendor’s invalid IP address to the hosts file to prevent the virus definition file from being downloaded and to prevent detection.

×：Social engineering

Social engineering is wrong because it does not require querying DNS servers. Social engineering refers to manipulation by an individual for the purpose of gaining unauthorized access or information.

×：Domain Litigation

Domain litigation is wrong because it does not involve poisoning the DNS server cache. Domain names are at trademark risk, including temporary unavailability or permanent loss of established domain names.

The data link layer or Layer 2 of the OSI model adds a header and trailer to the packet to prepare the packet in binary format in local area network or wide area network technology for proper line transmission. Layer 2 is divided into two functional sublayers. The upper sublayer is logical link control (LLC), which is defined in the IEEE 802.2 specification. It communicates with the network layer above the data link layer. Below the LLC is the Media Access Control (MAC) sublayer, which specifies interfaces with the protocol requirements of the physical layer.

Carrier Sense Multiple Access Collision Detection (CSMA / CD) is used for systems that can transmit and receive simultaneously, such as Ethernet. If two clients listen at the same time and make sure the line is clear, both may transmit at the same time, causing a collision. Collision Detection (CD) is added to solve this scenario. The client checks to see if the line is idle and transmits if it is idle. If in use, they wait for a random time (milliseconds). During transmission, they monitor the network and if more input is received than transmitted, another client is also transmitting and sends a jam signal instructing other nodes to stop transmitting, wait a random time and then start transmitting again.

UDP (User Datagram Protocol) floods are often used in distributed denial of service (DDOS) attacks because they are connectionless and yet allow for easy generation of UDP messages from various scripting and compilation languages. UDP is a datagram protocol.

〇：How routers are centrally managed and control packets based on the controller’s instructions 

Software-defined networks (SDN) are intended to facilitate centralized management of routing decisions and to separate the router’s logical functions of passing data between the routing decision and the interface and making its mechanical functions.SDN architecture is a scalable, a programmable, and is intended to be a standard method of providing router control logic. Therefore, the correct answer is “a way for routers to be centrally managed and control packets based on the controller’s instructions.

×：Mapping between MAC and IP addresses.

ARP table.

×：Updating the routing table in a dynamic way.

Explanation of dynamic routing.

×：A method in which routers communicate with each other to update the routing table when an event occurs.

This is an explanation of routing control in case of communication failure.

〇：Teardrop

Teardrop is an attack to bring a system to a halt by forging the offset of IP packets when they are returned before splitting.

×：Fraggle attack

Fraggle attack is an attack that uses the CHARGEN function to generate an appropriate string.

×：CHARGEN attack

There is no attack with such a name.

×：War Driving

Wardriving is the act of driving around a city looking for vulnerable wireless LAN access points.

〇：Make the mail relay server available to everyone.

This is a question of choosing the “ineffective” one. An open mail relay server is not an effective countermeasure against spam. In fact, spammers often use spammers to distribute spam, because the attackers can hide their identities. An open mail relay server is an SMTP server configured to allow inbound SMTP connections from anyone on the Internet, and many relays are properly configured to prevent attackers from distributing spam and pornography. Thus, the correct answer is “have an email relay server available to everyone.” will be.

×：Build a properly configured mail relay server.

A properly configured mail relay server can also suppress spam mail.

×：Perform filtering at the e-mail gateway.

Filtering emails that are considered spam mail at the gateway will help to prevent spam mail.

×：Filtering at the client.

Filtering spam mail at the client, i.e., in a mailing application such as Outlook, is considered to be a countermeasure against spam mail.

Computer worms are standalone malware computer programs that replicate themselves and spread to other computers. They typically operate at OSI reference layers 5-7.

Circuit switching is a dedicated communication channel through a network. The circuit guarantees full bandwidth. The circuit functions as if the nodes were physically connected by cables.

〇：Socket

UDP (User Datagram Protocol) and TCP (Transmission Control Protocol) are transport protocols used by applications to retrieve data over a network. Both use ports to communicate with the upper OSI layer and keep track of the various conversations that occur simultaneously. Ports are also the mechanism used to identify how other computers access services. When a TCP or UDP message is formed, the source and destination ports are included in the header information along with the source and destination IP addresses. This IP address and port number is called a socket; the IP address serves as the gateway to the computer and the port serves as the gateway to the actual protocol or service.

×：IP address

This is incorrect because the IP address does not tell the packet how to communicate with the service or protocol. The purpose of an IP address is to identify and address the location of a host or network interface. Each node in a network has a unique IP address. This information, along with the source and destination ports, make up a socket. The IP address tells the packet where to go, and the port indicates how to communicate with the appropriate service or protocol.

×：Port

The port is incorrect because it tells the packet only how to communicate with the appropriate service or protocol. It does not tell the packet where it should go. The IP address provides this information. Ports are communication endpoints used by IP protocols such as TCP and UDP. Ports are identified by a number.

×：Frame

Frame is incorrect because the term is used to refer to a datagram after the header and trailer have been given to the data link layer.

Point-to-Point Tunneling Protocol (PPTP) is a way to implement a virtual private network (VPN). It is Microsoft’s proprietary VPN protocol that operates at the data link layer of the OSI model; PPTP can only provide a single connection and can operate over a PPP connection.