How to use this sheet
This is a review sheet, not a course. It does not cover everything on the exam, and CompTIA says its example lists are not exhaustive. Use the objectives on CompTIA’s Network+ page as your checklist and this page as a final skim. For depth, see the domains explained page.
Exam facts at a glance
| Item | Value (CompTIA, checked October 22, 2026) |
|---|---|
| Code | N10-009 (Network+ V9) |
| Questions | Maximum of 90, multiple-choice and performance-based |
| Time | 90 minutes |
| Passing score | 720 on a scale of 100 to 900 |
| Domains | Concepts 23%, Implementation 20%, Operations 19%, Security 14%, Troubleshooting 24% |
| Validity | Three years, renewable through CE |
Domain 1: Networking Concepts (23%)
Key ideas
- OSI layers from 1 to 7: physical, data link, network, transport, session, presentation, application. Switch = layer 2, router = layer 3, ports and TCP/UDP = layer 4.
- Appliances: firewall filters traffic, IDS detects, IPS detects and blocks, load balancer spreads requests, proxy stands in for clients.
- Fiber: single-mode for long distances, multimode for shorter runs.
- Private ranges (RFC 1918): 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16. APIPA is 169.254.0.0/16.
Ports to know cold
| Port | Service | Port | Service |
|---|---|---|---|
| 20/21 | FTP data/control | 123 | NTP |
| 22 | SSH, SFTP | 161/162 | SNMP poll/trap |
| 23 | Telnet | 389 / 636 | LDAP / LDAPS |
| 25 | SMTP | 443 | HTTPS |
| 53 | DNS | 445 | SMB |
| 67/68 | DHCP server/client | 3389 | RDP |
| 69 | TFTP | 110 / 143 | POP3 / IMAP |
| 80 | HTTP | 514 | Syslog |
Usable hosts by prefix
| Prefix | Usable hosts | Prefix | Usable hosts |
|---|---|---|---|
| /24 | 254 | /28 | 14 |
| /25 | 126 | /29 | 6 |
| /26 | 62 | /30 | 2 |
| /27 | 30 |
Easily confused
- SASE is networking plus security from the cloud; SSE is the security half.
- North-south traffic enters or leaves the data center; east-west moves between servers inside it.
- NAS shares files over the network; SAN presents block storage.
Decision rule. If a scenario asks for a subnet that fits N hosts, add two for the network and broadcast addresses, then pick the smallest block that fits.
Domain 2: Network Implementation (20%)
Key ideas
- A VLAN splits one switch into separate broadcast domains. Different VLANs need a Layer 3 device to talk.
- A trunk carries several VLANs, tagged with 802.1Q. Untagged traffic uses the native VLAN.
- Spanning tree prevents Layer 2 loops. Link aggregation bundles ports for bandwidth and redundancy.
- NAT translates addresses; PAT lets many hosts share one public address using ports.
- Wi-Fi bands: 2.4 GHz reaches farther and is crowded; 5 GHz and 6 GHz are faster and shorter-range. Channels 1, 6 and 11 do not overlap on 2.4 GHz.
Easily confused
- SSID is the network name; BSSID identifies one access point radio, usually by its MAC address.
- Static routes are manual; dynamic protocols (OSPF, EIGRP, BGP) learn. BGP is between networks, OSPF and EIGRP inside one.
- IDF is a closet serving a floor or area; MDF is the main distribution room.
Decision rules
- If two routes match, think longest prefix first, then lowest administrative distance, then lowest metric.
- If hosts in one VLAN work and cross-VLAN traffic fails, check the Layer 3 interface or gateway before the cable.
Domain 3: Network Operations (19%)
Key ideas
- Documentation: diagrams, asset inventory, IP address management, SLAs.
- Monitoring: SNMP, flow data, syslog, packet capture, port mirroring.
- Disaster recovery: hot site is ready now, warm is partly ready, cold is empty space.
- DNS records: A (IPv4), AAAA (IPv6), CNAME (alias), MX (mail), PTR (reverse), TXT (text), NS (name server), SRV (service).
Easily confused
- RPO is how much data you can lose; RTO is how long you can be down.
- MTBF is time between failures; MTTR is time to repair.
- DHCP reservation always gives the same address to one device; exclusion keeps addresses out of the pool.
- Site-to-site VPN joins two networks; client-to-site connects one user. Split tunnel sends only some traffic through the VPN.
- In-band management uses the production network; out-of-band keeps working when it is down.
Decision rule. If the scenario says “must stay reachable during an outage”, think out-of-band access or a redundant path.
Domain 4: Network Security (14%)
Key ideas
- CIA triad: confidentiality, integrity, availability.
- 802.1X has a supplicant (device), authenticator (switch or AP) and authentication server (often RADIUS).
- Authentication proves who you are; authorization decides what you may do; accounting records what you did.
- Common defenses: ACLs, port security, NAC, content filtering, hardening, screened subnets.
Attack and symptom pairs
| Symptom | Think |
|---|---|
| Switch floods frames to all ports | MAC flooding |
| Hosts send traffic to the wrong gateway MAC | ARP poisoning |
| Fake access point with a familiar SSID | Evil twin |
| Unknown access point plugged into a wall port | Rogue AP |
| Attacker sees tagged traffic from another VLAN | VLAN hopping |
| Traffic is read between two parties | On-path attack |
Decision rule. Match the control to the layer: port security for switch ports, ACLs for traffic rules, 802.1X for who may join.
Domain 5: Network Troubleshooting (24%)
The method. Identify the problem, establish a theory, test it, plan, implement, verify, document. Do not fix before you test the theory.
Tools and what they answer
| Tool | Answers |
|---|---|
| ping | Is the host reachable? |
| traceroute | Where along the path does it stop? |
| nslookup, dig | Does name resolution work? |
| netstat | Which connections and ports are open? |
| arp | Which MAC goes with this IP? |
| Protocol analyzer | What is on the wire? |
| Cable tester, toner probe | Is the cable good, and which one is it? |
Decision rules
- A 169.254.x.x address on a client means it did not get a DHCP answer. Check the pool, the relay and the path.
- Works by IP but not by name: think DNS.
- Late-night slowness on one link: think congestion. Slowest hop for everyone: think bottleneck.
- CRC errors, runts and giants point to the physical layer or a duplex or MTU mismatch.
Common traps across domains
- Choosing the answer that is true in general but ignores a constraint in the scenario.
- Skipping “choose two” in the stem.
- Picking a tool that checks the wrong layer.
- Counting 32 hosts in a /27 instead of 30.
Last-day checklist
- Re-read the port table and the usable-host table once.
- Skim the confusable pairs above out loud.
- Run a short timed set, not a full one.
- Prepare ID and your booking details. The exam day guide lists what to check.
- Sleep. A rested mind beats one more hour of cramming.
More guides for N10-009
- Network+ N10-009 Exam Format and Scoring
- Network+ N10-009 Study Plan: 4 and 8 Weeks
- Is Network+ N10-009 Hard? An Honest Look
- Network+ N10-009 Prerequisites
- N10-009 Renewal and Retakes Explained
- Is N10-009 Worth It? An Honest Look
- N10-009 vs SY0-801: Which First?
- CCNA vs Network+: Which Exam First?
Next step
Test what stuck with the sample questions, or return to the exam overview. The N10-009 practice tests offer original practice questions for a full timed run.