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Networking Overview

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Networking Overview

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Security+ Study Guide


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[edit section] Networking Overview

In subsequent chapters of this study guide, we will take a look at different security topologies or ways that networks can be set up with security in mind. Before we can do this, however, we must have a clear understanding of different networking devices and concepts. We will now very briefly describe different key networking components to help you understand how they are related to information security and the exam.

A cartoon-ish network

[edit section] IP Address

An IP address is a unique numeric identifier of a host machine within the scope of a TCP/IP network. Public IP addresses are unique and individual to each host in the world, while private IP addresses are often duplicated among different private networks. You can think of a public IP address as a sort of telephone number and the private IP address as a sort of extension system that operates “in-house.” All IP addresses are formed as four octets separated by a dot: for example, is a commonly-used private IP address.

[edit section] NAT

NAT, or Network Address Translation, is a service in which a gateway can allow multiple private hosts to operate under the guise of a single public IP address. One of the implications of NAT is that hosts “behind” the NAT are effectively “hidden” from the rest of the Internet, with the NAT acting as a sort of packet filtering firewall.

[edit section] Router

A router can forward packets of information based on the IP address of the header of the packet. Think of the header of the packet as a sort of shipping label for the packet in which the contents (the package) are contained. A router can quickly examine the shipping label and send it off to the appropriate destination.

[edit section] Gateway

A gateway serves as a sort of middle-man between two networks, usually the Internet and a private network. Many routers also serve as gateways, and many gateways have NAT functionality built into them.

[edit section] Media

The term “media” in networking refers to the physical medium of communication that the network utilizes. In many Ethernet networks CAT-5 cabling is employed. In high-speed applications, fiber optic media is used.

[edit section] Applications and Ports

Applications, in the networking sense, refer to specific Application-layer services that hosts provide over specific ports, or gateways into the system. For example, a web server is an application server that provides web pages over the port TCP 80. Other Application servers include FTP, Telnet, SSH, and Media servers.

[edit section] Firewall

A firewall is a device that can selectively filter communications between two hosts. Although we have an entire article dedicated to firewalls, it never hurts to reinforce the concept of what a firewall is for your own extended understanding.

[edit section] Switch/Hub

Hosts are connected to each other via a switch or a hub. The difference between a switch and a hub is that a hub forwards all packets to all connected hosts whereas a switch forwards packets only to selected recipients, increasing information confidentiality.

[edit section] DMZ Host

A DMZ host is basically a “catch-all” host for requests on non-configured ports. Through a DMZ host, undesirable network traffic can be sent to single safe host rather than any host that would be in danger from malicious traffic.

[edit section] Quick Review

1. Which of the following can be used as a sort of packet filtering firewall?

a. Proxy Server

b. Switch

c. NAT Device

d. None of the above

2. Why can’t a packet sniffer intercept switched network traffic?

a. The packet sniffer can only work in promiscuous mode

b. Switched networks direct traffic by MAC address

c. The packet sniffer can only work in latent mode

d. The port configuration is incorrect

3. Which of the following are not application services or servers? (Choose all that apply)

a. Proxy Server

b. Email Server

c. Web Server

d. DMZ Server

e. ARP Server

f. DHCP Server

[edit section] Answers:

1. Only an NAT device would actually block packets based on headers (the definition of a packet filtering firewall) because an NAT device would categorically block incoming traffic that has not established a session. The answer is C.

2. A switch only forwards traffic to the intended recipient via MAC address (just like a router only forwards traffic to the recipient via IP address), so the answer must be B.

3. D, E, and F are all non-application servers. DMZ servers are non-existent, and DMZ hosts would nominally operate in the network layer of the OSI model. ARP servers would operate in the Data-Link layer of the OSI model, and DHCP servers would operate in the Network layer of the OSI model.

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