CompTIA A+ Core Certification: A Simple Guide To Networking - Services Provided by Networked Hosts

220-1101: Objective 2.4: Summarize services provided by networked hosts.
As computer networks have evolved over time, different technologies have emerged to perform specific tasks, or server roles, for the network. The following sections describe some of the common server roles that perform specialized tasks for the users on a network. A server might not necessarily be a computer. For example, routers often incorporate one or more of the server functions described in the following sections.

DNS Server
A Domain Name System (DNS) server has a database that contains public IP addresses and their associated domain names. The purpose of a DNS server is to translate domain names used in web page requests into IP addresses. DNS server functions are included in SOHO routers. For larger networks, a separate DNS server can be used. A DNS server communicates with other, larger DNS servers if the requested addresses are not in its database.

DHCP Server
A DHCP server supports Dynamic Host Configuration Protocol, the protocol that automatically assigns IP addresses to connected devices on a network. DHCP server functions are included in SOHO routers and are typical roles for domain controllers on small to medium business (SMB) networks. On larger networks, DHCP servers are often separate physical or virtualized servers.

File Server
A file server is used to provide shared storage on a network. A file server is typically a computer with a single large drive or a RAID array for storage. Dedicated servers are used only for storage; a computer that shares storage and also performs standalone tasks (as in a Windows workgroup with 10 or fewer systems) is known as a nondedicated server.
A network-attached storage (NAS) device is a special kind of file server designed to store large amounts of data in a central location for users on the network. A NAS is essentially one or more drives fitted with an Ethernet connection; it is assigned its own IP address.
Fileshare is a specialized data server system that allows for efficient processing of files that many users across a network access at one time.

Print Server
A print server manages the printing tasks for multiple users who share one or more printers in an office. Printing a document in a large office was once a complicated task because printers were expensive and access to them was limited. Eventually, a designated computer and printer became hosts on an office network, and managing printing tasks for the whole office became more efficient. Because print jobs might be requested faster than a printer can deliver them, print servers queue print jobs and deliver them to appropriate printers when they are available. They can also track the usage of printers on the network. Print servers and printers can be either wired or wireless.

Mail Server
A mail server sends or receives email on a network. An SMTP (Simple Mail Transfer Protocol) server is used to send outgoing email, and either a POP3 (Post Office Protocol version 3) or IMAP (Internet Message Access Protocol) server is used to receive mail. Mail server platforms are available from many vendors. For example, Microsoft Exchange Server is a popular mail server platform that includes email, contacts, calendar, scheduling, and more.

Syslog Server
Syslog servers track and log events that happen on devices (such as routers, switches, and firewalls) and printers on a network. Devices on a network usually have a way to track their system events, such as user logins and crashes, as well as other activities that the network administrator has determined to be important. The reports are sent to a central syslog server for network managers to analyze, as needed.

Web Server
Web servers are specialized computers that host websites and provide various types of content to clients via the Internet. A web server uses HTTPS to communicate with computers on other networks that are requesting information. Web hosting is essential in business and education, and setting up a web server has been a common task for an IT professional for many years. Today many companies use cloud-based web servers such as Amazon Web Services (AWS) Cloud, Microsoft Azure, and Google Cloud.

Authentication, Authorization, and Accounting (AAA) Server
An AAA server is used to examine and then verify or deny credentials to a user who is attempting to log into secured networks. Usernames and permissions are stored in this central server, which provides security certificates to users and records user logins to the network.
The authorization function of an AAA server refers to making sure users access only areas where they have permission to go. After users are authenticated, their level of authorization is determined and enforced.
The accounting function of an AAA server refers to keeping track of the resources and activities a user has performed while on the network. Accessing files and billing for services are examples of accountable activities.

Internet Appliances
Internet appliances are single-purpose devices that are used to perform specific tasks on an IP network.

Spam Gateways
Email is essential to business. In the past, email spam has comprised up to half of the email traffic on the Web. Spam gateways are email filters that can detect almost all spam coming into a system, which increases email efficiency and network security as well. These gateways can be on-premises and attached to the email server or can be cloud based, depending on how email is structured in an institution.

UTM
Unified threat management (UTM) devices provide firewall, remote access, virtual private network (VPN) support, web traffic filtering with anti-malware, and network intrusion prevention. UTM devices can be specialized boxes that are placed between the organization’s network and the Internet, but they can also be virtual machines that use cloud-based services. UTM devices unite the functions of several earlier devices and have largely replaced IDS and IPS devices (described next). Barracuda Networks, Check Point, Cisco, and other networking equipment manufacturers offer versions of UTM devices.

IDS
An intrusion detection system (IDS) device or program detects network intrusions that a firewall might not detect. Typical threats that an IDS can detect include attacks against services, malware attacks, data-driven attacks, and host-based attacks. To detect these threats, a typical IDS uses signature-based detection, detection of unusual activities (anomalies), and stateful protocol analysis. To maintain protection, an IDS device or program must be updated frequently with new signatures and rules.
A true IDS does not block attacks, but some products and services referred to as IDSs actually have characteristics of IPSs (intrusion prevention systems).

IPS
An intrusion prevention system (IPS) uses methods similar to those used by an IDS. Unlike an IDS, however, an IPS blocks attacks. Dedicated IDS and IPS devices are not widely used today, but their features are incorporated into UTM devices.
An IPS can also be implemented in software with a package such as the open source Snort (www.snort.org) for Windows and some Linux distributions.

Load Balancers
Load balancing refers to sharing tasks and traffic in a network for maximum efficiency. When balancing traffic within a network or handling application processing between servers, the work is shared among all the available resources on a network instead of occurring on only one device. For example, network load balancing occurs when inbound or outbound traffic can be split up and routed to the destination in different ways to enhance speed, with the data reassembled at the destination for processing. A load balancer increases redundancy and performance by distributing the load to multiple servers. Network load balancers are often reverse proxy servers configured in a cluster to provide scalability and high availability.

Proxy Server
A proxy server is an intermediary between a client and another network, such as the Internet. A proxy server stores web pages that have been requested; if a client requests a web page, the proxy server checks its cache for the page. If the page exists and is up-to-date, the proxy server uses its cached copy to supply the client request. If the proxy server does not have the requested page, it downloads the page on behalf of the client, sends the page to the client, and retains a copy of the page in its cache.
A proxy server reduces traffic between a network and the Internet, and it can also block requests for undesirable traffic. In addition, proxy servers can be used for anonymous surfing. See https://whatis.techtarget.com/definition/proxy-server for more information on how proxy servers are used.

Legacy and Embedded Systems
The term legacy refers to something handed down from predecessors. Legacy systems, therefore, are systems that use outdated operating systems, programming languages, applications, or hardware. Maintaining legacy systems is often necessary when newer products are not compatible with legacy applications (for example, applications that can run only under MS-DOS or old versions of Windows).
If a legacy operating system and its applications can be run in a virtualized environment, the problems of maintaining old hardware are eliminated.
 

Embedded systems are dedicated computing devices used for specific tasks, such as machine control, point-of-sale systems, or ATMs. Embedded systems commonly are found in Supervisory Control and Data Acquisition (SCADA) systems. SCADA systems are designed to provide centralized control for managing industrial equipment, such as in manufacturing or water and waste treatment plants. SCADA systems connect equipment to a typically secure network that facilitates communication between operators and machines. Operators can collect and analyze data from various components, as well as modify configurations or operations. SCADA systems can be complex because many different components are working together to ensure the functionality of the equipment or process. Embedded systems often also are legacy systems; as long as they work, they are maintained. Embedded systems are very specialized in nature and often run older operating systems because of the way the systems are designed and whether they allow the manufacturer to upgrade the operating system.
Perhaps the biggest risk to both legacy and embedded systems is security. If a legacy system or an embedded system has network or Internet connectivity, it theoretically could be attacked or used as a bot to attack other systems. This is a great concern for organizations that utilize SCADA systems because many manage critical infrastructure equipment in facilities such as power plants, dams, nuclear reactors, and water and waste treatment. Although operating systems designed for embedded uses have more security than standard operating systems, older operating systems face the greatest risks.
Because of the potential for security risks, some organizations have paid for extended security updates for otherwise-legacy systems.

When considering whether and when to update legacy systems or embedded systems, consider these issues:
Will the existing data be usable with newer apps?
Can the existing program run with current operating systems?
Will changes in network security, wireless, or Internet standards (such as a changeover to IPv6) cause problems with the application?
Can a proprietary application be licensed to run in a virtual machine?
Does existing hardware used in the embedded system work with the new operating system?
Does the embedded application run on current embedded operating systems? If not, is an updated version available?

Evaluating, testing, troubleshooting, and running both systems in parallel are highly advisable when updating legacy systems or embedded systems.

Internet of Things (IoT) Devices
The Internet has long connected people together, but in recent years, the explosive growth of the Web has involved connections between people and the objects that they use. As communication protocols such as Bluetooth and Z-Wave have evolved, production techniques have made it easier to embed communication capability into smaller and less expensive objects that are common in people’s everyday life. Markets for Internet of Things (IoT) devices are expanding—consider phones, cars, home appliances, door locks, wall outlets, lights, and video-enabled doorbells, among many other devices. Industrial uses are being developed as well, and now devices can measure soil moisture, noise, motion, air pressure, and water pressure. Many billions of objects are now talking to each other and sharing data, and the number of such devices is expected to grow exponentially.

Figure depicts some of the many IoT functions you might already enjoy on your mobile device.



IoT Applications on a Mobile Device (Image © Es sarawuth, Shutterstock)

The software to manage IoT devices can be installed on computers or mobile devices. Typically, a vendor of an IoT product develops a mobile app to monitor and manage the product. Some systems are complex, but many are quite simple and easy to set up on a home network. The following are some items that can participate in the IoT:
Thermostats
Light switches
Security cameras
Door locks
Voice-enabled smart speakers/digital assistants

Figure shows the user interface for an IoT-enabled wall outlet adapter that is monitoring energy use for a refrigerator. Off/on and scheduling capability are built into the application, and the device can be managed from anywhere on the Web.



IoT Device App Interface