Networking · Topic 5 of 10
Services Provided by Networked Hosts
Summarise server roles such as DNS, DHCP, file, print, mail and syslog, plus internet appliances, legacy and embedded systems, SCADA and IoT devices.
- 4 min
- DNS maps names to addresses; DHCP assigns addresses and settings.
- A file server shares files; a print server shares printers and holds queues.
- Syslog gathers logs in one place for review.
What it is
A networked host is any device on a network. Some hosts act as servers and offer a service that other hosts, called clients, use.
This page covers common server roles, appliances that protect or balance traffic, and special systems such as embedded devices and industrial control.
How it works
A server is defined by what it does. One physical machine can carry several roles, or each role can have its own machine or virtual machine.
Common server roles
| Role | What it does |
|---|---|
| Domain Name System (DNS) server | Turns names such as a website name into Internet Protocol (IP) addresses |
| Dynamic Host Configuration Protocol (DHCP) server | Hands out IP addresses and settings to clients |
| File share server | Stores shared files and controls who can open them |
| Print server | Shares printers and holds the print queue |
| Mail server | Sends, receives and stores email |
| Web server | Serves web pages to browsers |
| Syslog server | Collects log messages from many devices in one place |
| Authentication, authorization and accounting (AAA) server | Checks who a user is, what they may do and what they did |
AAA is the idea behind central login systems. Authentication proves identity, authorization grants rights, and accounting records activity.
A file server works best with permissions so users reach only what they need. A print server keeps one queue, which stops jobs from being lost when a printer is busy.
A database server stores structured data and answers queries from applications, for example a Structured Query Language (SQL) database behind a web application. It is usually a separate server from the web server, with limited access and regular backups, because it holds the data that matters most.
Internet appliances
These are devices, often with software inside, that sit in the path of traffic.
| Appliance | Purpose |
|---|---|
| Spam gateway | Filters unwanted and harmful email before it reaches users |
| Unified threat management (UTM) device | Combines several protections, such as a firewall, antivirus and content filter, in one box |
| Load balancer | Spreads requests across several servers so no single one is overloaded |
| Proxy server | Acts for clients when they reach other servers, and can filter or cache content |
Intrusion detection and prevention are often in a UTM. An intrusion detection system (IDS) watches and alerts, while an intrusion prevention system (IPS) can also block.
Legacy and embedded systems
A legacy system is old hardware or software that is still in use, often because a business process depends on it. It may lack updates, so it needs extra protection, such as isolating it on its own network segment.
An embedded system is a computer built into another device for a single task, such as a thermostat, a camera or a printer controller. Embedded devices have limited settings and slow update cycles.
SCADA
Supervisory control and data acquisition (SCADA) systems monitor and control industrial equipment such as pumps, valves and power plants. They were designed for reliability, not security, and often run older software.
They should be kept away from general office networks and the internet.
Internet of Things
Internet of Things (IoT) devices are everyday objects that connect to a network, such as smart speakers, doorbells, thermostats and light bulbs. They are small, cheap and often have weak default security.
Change default passwords, update firmware and, where possible, place IoT devices on a separate network.
Embedded, legacy, SCADA and IoT systems are often hard to patch, so avoid leaving them on the same flat network as important data.
What to remember for the exam
- DNS maps names to addresses; DHCP assigns addresses and settings.
- A file server shares files; a print server shares printers and holds queues.
- Syslog gathers logs in one place for review.
- AAA stands for authentication, authorization and accounting.
- A spam gateway filters email; a UTM bundles several protections.
- A load balancer spreads requests across servers; a proxy acts for clients.
- Legacy systems are old but still in use; embedded systems are computers inside single purpose devices.
- SCADA controls industrial equipment, and IoT covers smart consumer devices.
Common mistakes
Mixing up DNS and DHCP. DNS answers "what is the address of this name"; DHCP answers "what address should this client use".
Assuming a proxy and a load balancer are the same. A proxy stands in for clients; a load balancer spreads load among servers.
Treating IoT as harmless. Cheap smart devices with default passwords are a common entry point for attackers.
Forgetting about legacy equipment. Old systems are often forgotten in updates, yet they stay on the network.
Confusing IDS and IPS. An IDS alerts; an IPS can block the traffic as well.
Check yourself
Which server role turns a name into an IP address?
A Domain Name System (DNS) server.
What does AAA stand for?
Authentication, authorization and accounting.
Why should IoT devices sit on a separate network?
They often have weak security and are hard to patch, so isolation limits the damage if one is compromised.
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