What the N10-009 exam looks like
| Item | Detail |
|---|---|
| Exam code | N10-009 |
| Questions | Maximum 90 |
| Time | 90 minutes |
| Format | Multiple choice and performance-based questions |
| Scoring | Scaled 100-900, passing score 720 |
| Networking Concepts | 23% |
| Network Implementation | 19% |
| Network Operations | 16% |
| Network Security | 19% |
| Network Troubleshooting | 23% |
Practice: addressing and subnetting
Do these with a timer. If any of them takes you more than about forty seconds, that is the gap to close before exam day - not through more theory, but through repetition until the numbers are recall.
A workstation shows an IP address of 169.254.11.7. What does this tell you?
That the host failed to obtain an address from DHCP and self-assigned an APIPA address. The 169.254.0.0/16 range is link-local: the machine can talk to others on the same segment that also self-assigned, but it has no gateway and no internet. The troubleshooting direction is the DHCP server, the relay or the physical path to it - not the workstation's TCP/IP stack.
How many usable host addresses are in a /26 network?
62. A /26 leaves six host bits, giving 64 addresses, minus the network address and the broadcast address. The recall you want is the table for the last octet - /24 is 254 usable, /25 is 126, /26 is 62, /27 is 30, /28 is 14, /29 is 6, /30 is 2 - so that you read the answer off rather than deriving it under time pressure.
Which private address ranges are defined by RFC 1918?
10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16. The 172.16 range is the one people misremember, because the /12 means it runs from 172.16.0.0 to 172.31.255.255 rather than stopping at 172.16. Expect at least one question that hinges on whether a given 172.x address is inside the private range.
A device needs to reach a host on a different subnet but cannot, while other devices on its own subnet are reachable. What should you check first?
The default gateway configuration on the device. Local communication working proves the interface, cable, switch port and IP address are functional; the failure is specifically in leaving the subnet, which is the gateway's job. Subnet mask errors produce the same symptom, so check both.
Practice: protocols, services and the OSI model
At which OSI layer does a switch primarily operate?
Layer 2, the data link layer, because it forwards frames using MAC addresses. Routers operate at Layer 3 using IP addresses, hubs at Layer 1 because they simply repeat electrical signals, and a multilayer switch does both Layer 2 and Layer 3. The reliable method for OSI questions is to identify what the device or protocol addresses - electrical signal, MAC, IP, port, or application data - and read the layer off from that.
Users can reach websites by typing an IP address but not by using the hostname. What is the likely cause?
A DNS problem - an unreachable or misconfigured DNS server, or bad records. This is one of the most reliably examined symptom-to-cause pairings on the exam, because it cleanly separates name resolution from connectivity. If neither the IP nor the name worked, the fault would be routing or the physical path instead.
Which DNS record type maps a hostname to an IPv4 address?
An A record. Keep the family straight: AAAA maps to an IPv6 address, CNAME creates an alias pointing to another name, MX identifies mail servers, PTR performs reverse lookup from address to name, and TXT holds arbitrary text used for verification records such as SPF.
Which protocol and port would you use for an encrypted command-line session to a network device?
SSH on TCP port 22. Telnet on port 23 does the same job unencrypted and is the wrong answer whenever the question mentions security. Ports are heavily examined, so drill at least 20, 21, 22, 23, 25, 53, 67, 68, 69, 80, 110, 143, 161, 389, 443, 445, 3389.
Two devices are plugged into the same switch, both links are up, but they cannot communicate. What is the most likely cause?
They are in different VLANs. A VLAN is a separate broadcast domain, so traffic between them requires a router or a Layer 3 switch regardless of physical proximity. The clue is that the physical layer is explicitly reported as healthy, which pushes the fault up the stack.
Practice: troubleshooting methodology
CompTIA publishes a six-step method and examines it by position. Learn it as an ordered list: identify the problem, establish a theory of probable cause, test the theory to determine the cause, establish a plan of action and implement the solution, verify full system functionality and implement preventive measures, and document findings, actions and outcomes.
You have tested your theory and confirmed the cause. What is the next step?
Establish a plan of action to resolve the problem and implement the solution. A common wrong answer is to jump straight to implementing a fix without a plan, or to document - documentation is always last. If testing the theory had failed to confirm the cause, the correct step would have been to establish a new theory or escalate.
After resolving an issue, a technician confirms the user can work normally and applies a configuration change to stop it recurring. Which step is this?
Verify full system functionality and, if applicable, implement preventive measures. Note that both halves belong to the same step - verification and prevention are not separate stages, which is exactly what an exam question will test.
Which command would you use to trace the path packets take to a remote host and identify where they stop?
traceroute on Linux and macOS, or tracert on Windows. Match tools to symptoms: ping tests reachability and latency, ipconfig or ifconfig shows local configuration, nslookup or dig queries DNS, netstat shows active connections and listening ports, and arp shows the MAC-to-IP mappings the host has learned.
The two habits that protect your clock
Both of the big domains cost time rather than knowledge, and both have a mechanical fix.
First, make subnetting recall rather than arithmetic. Memorise the usable-host counts and the block sizes for the last octet so that a /27 immediately means blocks of 32 and 30 usable hosts. Deriving that from powers of two on every question is a minute you do not have.
Second, read troubleshooting scenarios backwards. Read the question sentence first, then the scenario, so you know what you are looking for while you read. These scenarios are deliberately padded with irrelevant detail, and reading forwards means processing all of it before you know what matters.
- ✓Handle performance-based questions the way most candidates do: flag them, clear the multiple choice, then return with the time you have banked.
- ✓There is no penalty for a wrong answer, so never leave a question blank.
- ✓A maximum of 90 questions in 90 minutes gives you a minute each on average - which is generous for recall and tight for anything you have to calculate.