Network Administrator key topics and quick reference
Some networking knowledge has to be understood, and some simply has to be remembered. The tables on this page cover the second kind: facts that questions assume you know instantly, such as which port a service uses or how far a cable can run. Use them for short, frequent review rather than long reading sessions.
How this guide was made
Written for this site with AI assistance, then checked automatically before publishing. The topic table, sample questions, worked examples and study plan are generated from this site’s question bank: each worked example is recalculated by separate code, and each sample answer says where it came from.
The guide deliberately states no salaries, grades, pass marks or exam dates. Those change, and they could not be checked here, so take them from the advert itself.
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Where to spend your study time
The suggested emphasis reflects what this position works with day to day. It is a study guide, not a published exam blueprint.
| Area | Suggested emphasis | Questions in the bank | Practise |
|---|---|---|---|
| Networking fundamentals | 31% | 2,636 | Networking |
| Routing and switching | 23% | 247 | Routing & Switching |
| Ports and protocols | 15% | 264 | Networking |
| Cybersecurity | 15% | 541 | Security |
| Hardware and operating systems | 8% | 961 | Hardware & OS |
| Linux command line | 8% | 360 | In the full bank |
How to use the reference tables
Read one table a day and test yourself on it the next morning before looking. For ports, cover the port column and name the port for each service, then reverse it. For the OSI model, practise placing protocols and devices on the right layer. Five minutes of recall does more than half an hour of rereading.
Quick reference
The OSI model
| Layer | Name | What happens here | Examples |
|---|---|---|---|
| 7 | Application | Services the user’s software talks to | HTTP, DNS, SMTP, SNMP |
| 6 | Presentation | Data formatting, encoding and encryption | Character encoding, TLS |
| 5 | Session | Opening, maintaining and closing sessions | Session setup and teardown |
| 4 | Transport | End-to-end delivery, ports, reliability | TCP, UDP |
| 3 | Network | Logical addressing and routing between networks | IPv4, IPv6, ICMP; routers |
| 2 | Data link | Frames and physical (MAC) addressing on one link | Ethernet, 802.11; switches |
| 1 | Physical | Signals on the medium | Copper, fibre, radio; connectors |
Ports worth knowing by heart
| Service | Port | Transport |
|---|---|---|
| FTP data | 20 | TCP |
| FTP control | 21 | TCP |
| SSH (and SFTP, which runs over it) | 22 | TCP |
| Telnet | 23 | TCP |
| SMTP | 25 | TCP |
| DNS | 53 | TCP and UDP |
| DHCP server | 67 | UDP |
| DHCP client | 68 | UDP |
| TFTP | 69 | UDP |
| HTTP | 80 | TCP |
| Kerberos | 88 | TCP and UDP |
| POP3 | 110 | TCP |
| NTP | 123 | UDP |
| NetBIOS name service | 137 | UDP |
| NetBIOS session | 139 | TCP |
| IMAP | 143 | TCP |
| SNMP | 161 | UDP |
| SNMP trap | 162 | UDP |
| LDAP | 389 | TCP |
| HTTPS | 443 | TCP |
| SMB over TCP | 445 | TCP |
| SMTPS | 465 | TCP |
| Syslog | 514 | UDP |
| SMTP submission | 587 | TCP |
| LDAPS | 636 | TCP |
| IMAPS | 993 | TCP |
| POP3S | 995 | TCP |
| MSSQL | 1433 | TCP |
| Oracle DB | 1521 | TCP |
| MySQL | 3306 | TCP |
| RDP | 3389 | TCP |
| PostgreSQL | 5432 | TCP |
| VNC | 5900 | TCP |
| HTTP alternate | 8080 | TCP |
Special IPv4 address ranges
| Range | Purpose |
|---|---|
| 10.0.0.0/8 | Private addressing (RFC 1918) |
| 172.16.0.0/12 | Private addressing (RFC 1918): 172.16.0.0 to 172.31.255.255 |
| 192.168.0.0/16 | Private addressing (RFC 1918) |
| 100.64.0.0/10 | Carrier-grade NAT shared space (RFC 6598) |
| 127.0.0.0/8 | Loopback |
| 169.254.0.0/16 | Link-local (APIPA): a host that failed to get a DHCP lease |
Common Ethernet cabling limits
| Cable | Typical use | Distance |
|---|---|---|
| Cat5e | 1 Gbps (1000BASE-T) | 100 m |
| Cat6 | 1 Gbps; 10 Gbps over short runs | 100 m at 1 Gbps; about 55 m at 10 Gbps |
| Cat6A | 10 Gbps (10GBASE-T) | 100 m |
| OM3 multimode fibre | 10GBASE-SR | up to 300 m |
| OM4 multimode fibre | 10GBASE-SR | up to 400 m |
| OS2 single-mode fibre | 10GBASE-LR | up to 10 km |
The ideas that connect
Networking topics lean on each other. Addressing decides what a router must do, routing decides whether traffic can leave the local network, NAT translates private addresses so traffic can reach the internet, and DNS turns names into the addresses all of that depends on. When a question seems to jump between topics, it is usually following this chain.
Things to be able to explain in a sentence
- Why a /24 network has 254 usable host addresses.
- What a trunk port carries that an access port does not.
- Why a device with a 169.254 address cannot reach the internet.
- What spanning tree prevents.
- How NAT lets many private devices share one public address.
- The difference between TCP and UDP, with one service that uses each.
Common questions
Do I need to memorise the whole ports table?
Learn the common services first, especially those used to manage and secure networks, such as SSH, DNS, DHCP, SNMP and syslog. Add the rest gradually during review.
Which OSI layer matters most?
Layers 2 and 3 carry most networking questions, because they explain the difference between switching and routing. Troubleshooting questions, though, expect you to move through every layer in order.
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