learn/network-plus
N10-009 study notes written objective by objective, with cited sources, protocol behaviour captured from running networks rather than drawn, and practice questions that link back to the material.
83 topics.
Study tools
Study plan
Topics across weeks, with each week returning the following one. Spacing beats cramming.
Objective coverage
All 25 N10-009 objectives, which are covered, and which are not.
Platform differences
All 53 differences from the topics, collected in one place. A vendor-neutral exam tests exactly this.
Full practice exam
Weighted to the real domain percentages and timed to 90 minutes.
Practice
Domain 1: Networking Concepts
Original practice questions for domain 1 of the CompTIA Network+ N10-009 objectives, written from the published objectives and vendor documentation.
Domain 2: Network Implementation
Original practice questions for domain 2 of the CompTIA Network+ N10-009 objectives, written from the published objectives and vendor documentation.
Domain 3: Network Operations
Original practice questions for domain 3 of the CompTIA Network+ N10-009 objectives, written from the published objectives and vendor documentation.
Domain 4: Network Security
Original practice questions for domain 4 of the CompTIA Network+ N10-009 objectives, written from the published objectives and vendor documentation.
Domain 5: Network Troubleshooting
Original practice questions for domain 5 of the CompTIA Network+ N10-009 objectives, written from the published objectives and vendor documentation.
Lessons
00Start here
What the CompTIA Network+ exam is, why the subject is worth certifying when every other exam assumes it, how these lessons are built, how to get something to practise on when you cannot buy a switch, and what is in the track.
network-plusnetworkingorientation01What a network actually is
A cable between two computers does not make a network. What else has to be true, why one machine needs two different addresses, and the arithmetic that decides whether your neighbour is reachable at all.
network-plusnetworkingbeginner02MACs, IPs and ports
A MAC address, an IP address and a port number identify the same machine at the same moment, and they are not competing answers. What each one is for, how all three travel inside one frame, and which of them survives a trip through a router.
network-plusnetworkingbeginner03The OSI model
The OSI model names the parts of a system you have already seen working. What each layer adds, why encapsulation is the mechanism behind it, which model the protocols on your machine actually follow, and the two layers nothing you will meet implements separately.
network-plusnetworkingbeginner04The boxes on a network
Routers, switches, firewalls, load balancers, proxies and the rest, sorted by the one question that actually separates them: how far into a frame does this thing read before it acts.
network-plusnetworkingbeginner05IPv4 addresses and the mask
An IPv4 address is 32 bits and the mask is a line drawn through them. Where that line falls decides which addresses are neighbours, which two you cannot give to anything, and why the obvious answer to how many machines fit is wrong twice.
network-plusnetworkingsubnettingbeginner06Subnetting by hand
Splitting a network is the other half of subnetting, and it works in the opposite direction from reading one. Borrowing bits, why a requirement for six networks gets you eight, how to turn a machine count into a prefix, and laying the ranges out with nothing overlapping.
network-plusnetworkingsubnetting07Address classes, private ranges and APIPA
Some IPv4 ranges are special and knowing which is worth more than it looks. The classes and why they are obsolete but still examinable, the three private ranges, loopback, and what a 169.254 address is actually reporting.
network-plusnetworkingaddressingbeginner08IPv6 addressing
IPv4 ran dry in February 2011 and the internet carried on, which is the fact worth explaining. What 128 bits buys, how to read and shorten a hex address, the link-local address your machine configured without being asked, and the three ways networks run both protocols at once.
network-plusnetworkingipv609TCP, UDP and the handshake
TCP sets up a connection, numbers everything, and resends what goes missing. UDP does none of that on purpose. The handshake packet by packet, what retransmission actually costs, the state that lingers after a close, and why a video call chooses the protocol that gives up.
network-plusnetworkingtcpudp10Ports and the protocols that use them
A firewall rule says 443 and nobody explains what that means. The ports this exam expects you to know, a way to learn them that is not brute repetition, the plaintext and encrypted pairs, and the uncomfortable fact that a port number guarantees nothing at all.
network-plusnetworkingportsprotocols11Copper cabling
Twisted pair looks the same whatever is printed on the jacket. Why the pairs are twisted at all, what a category number actually promises and why it is not a speed, when shielding helps and when it makes things worse, and the rating on the jacket that has nothing to do with data.
network-plusnetworkingcablingbeginner12Fibre and transceivers
Single mode and multimode look identical and are not interchangeable. What actually differs inside the glass, how the OM and OS numbers name it, the connectors and the transceiver form factors, and why a mismatched optic gives you a link that comes up and then fails.
network-plusnetworkingcablingfibre13Physical installations
Where cabling terminates and why the hierarchy exists, what a rack unit is, which way the air is supposed to travel and what happens when one switch disagrees, sizing power from the load, and the room conditions that decide whether any of it keeps running.
network-plusnetworkingphysicaldata-centre14How a switch learns
A switch is told nothing and works out where everything is by watching. How the forwarding table fills, what happens to a frame whose destination it has not learned yet, why entries expire, and what all of that means for anyone with a packet capture running.
network-plusnetworkingswitching15Unicast, multicast, anycast and broadcast
One packet and four different answers to who gets it. What each delivery type means on the wire, where the boundary of a broadcast actually sits, how multicast avoids sending the same thing twice, and the one that puts a single address in several countries at once.
network-plusnetworkingswitching16VLANs
One switch, two companies, and traffic that must never mix. What a VLAN separates and what it deliberately does not, why a VLAN is exactly a broadcast domain, and the demonstration that separates VLAN membership from subnet membership once and for all.
network-plusnetworkingswitchingvlans17Trunking and 802.1Q tagging
One cable between two switches carrying eight VLANs. Where the tag sits in the frame, the four bytes it costs, what the native VLAN is and why it causes arguments, and what happens when the two ends of a trunk disagree about any of it.
network-plusnetworkingswitchingvlans18Interface configuration and link aggregation
Speed and duplex, what auto-negotiation does when only one end is playing, why a duplex mismatch produces a slow link rather than a broken one, and what bonding two cables together actually buys you, which is not what most people expect.
network-plusnetworkingswitching19Spanning tree
Two switches, two cables between them, and the whole network stops. Why a layer 2 loop is fatal rather than merely wasteful, how the root bridge is elected, what the port states mean, and what running the protocol costs you.
network-plusnetworkingswitching20MTU and jumbo frames
Small requests work and large ones hang forever. What the MTU is, what fragmentation costs, how path MTU discovery is supposed to find the answer, and why blocking one kind of ICMP turns a working network into one that fails only for big packets.
network-plusnetworkingtroubleshooting21The routing table and static routes
A packet arrives for a network this machine is not on. The routing table is the list of decisions that answers what happens next: connected routes nobody typed, static routes somebody did, longest prefix match, and the default route as the answer of last resort.
network-plusnetworkingrouting22Dynamic routing protocols
Forty routers and a link that failed at three in the morning. Why dynamic routing exists, what distinguishes the three protocols this exam names, what an adjacency is, and what convergence looks like when you watch a network repair itself.
network-plusnetworkingrouting23Route selection
Two routes to the same place and only one goes in the table. The order the three tiebreaks are applied in, why prefix length beats everything including a much better metric, and what administrative distance is actually comparing.
network-plusnetworkingrouting24VLSM and planning an address space
Six subnets of wildly different sizes and one /22 to fit them in. Allocating largest first and why the order is not a preference, what summarisation buys and what it costs you if you allocate badly, and how to leave room to grow without wasting the space.
network-plusnetworkingsubnetting25NAT and PAT
Fifty machines behind one public address and everything works. What is actually being rewritten, the table that keeps the conversations apart, why incoming connections are the hard direction, and the reasons NAT is not the security control people believe it is.
network-plusnetworkingroutingnat26FHRP, virtual IPs and subinterfaces
The default gateway is a single point of failure that every machine on the network is configured to use. First hop redundancy as a concept, the virtual address two routers share, and the subinterfaces that let one physical link carry several networks.
network-plusnetworkingroutingredundancy27Topologies and architectures
The shapes networks are built in, why the data centre abandoned the one every textbook teaches, and what north-south and east-west actually describe. Star, mesh, hub and spoke, three-tier and spine and leaf, with the arithmetic that decides between them.
network-plusnetworkingdesignbeginner28SDN, SD-WAN and VXLAN
Two hundred branch offices and one policy change. What separating the control plane from the data plane actually buys, what SD-WAN does that a router does not, and VXLAN as layer 2 carried over layer 3 with the byte cost that comes with it.
network-plusnetworkingdesignoverlay29Wireless and cellular media
A radio link is a shared medium with no cable, and almost everything confusing about wireless follows from that one fact. What 802.11 is as a family, why the air is half duplex, and where cellular and satellite genuinely belong.
network-plusnetworkingwirelessbeginner30Wireless channels and frequencies
Twelve access points in one office and everything is slow. The three bands and what each trades, why only three channels fit in 2.4 GHz, what channel width actually buys, and the regulatory limits that decide what you are allowed to transmit.
network-plusnetworkingwireless31SSIDs, network types and access points
The same network name in every room and your laptop moving between them. What SSID, BSSID and ESSID each actually name, why roaming is the client's decision and not yours, the four network types, and what a controller changes.
network-plusnetworkingwireless32Wireless security and authentication
The password is on a whiteboard and forty people know it. What WPA3 changed and why it mattered, the operational difference between a shared key and per-user identity, what enterprise authentication actually involves, and why two protocols this subject is famous for are absent from the exam.
network-plusnetworkingwirelesssecurity33Security vocabulary and the CIA triad
Five words everybody uses and half of them mean something else. Risk, vulnerability, threat and exploit as four distinct things, why availability is a security property rather than an operations one, and what the triad is for.
network-plusnetworkingsecuritybeginner34Encryption, certificates and PKI
The padlock proves less than people think. Symmetric and asymmetric in one page, what a certificate actually binds and who vouches for it, and the chain of trust demonstrated by breaking it.
network-plusnetworkingsecuritypki35Identity and access management
The contractor left in March and the account still works. Authentication against authorisation as two separate questions, what multifactor actually requires, the four authentication services the exam names, and why RADIUS and TACACS+ are not interchangeable.
network-plusnetworkingsecurityidentity36Network documentation and diagrams
The person who built it left in 2019. Physical against logical drawings, why layer 2 is the diagram nobody has, what an asset inventory needs beyond a list of boxes, and what makes documentation survive contact with change.
network-plusnetworkingoperationsdocumentation37Lifecycle, change and configuration management
The switch stopped getting firmware updates two years ago and nothing changed on the day it happened. End of life against end of support, what change management is protecting, and why a backup config nobody has restored is not a backup.
network-plusnetworkingoperations38SNMP
A protocol from 1988 that most networks still run, and the two ways it delivers information. Polling against traps, what an object identifier actually is, and why the community string in a version 2c poll is not a password.
network-plusnetworkingmonitoring39Flow data, capture and port mirroring
Counters tell you how much. Flow data tells you who. Packet capture tells you what, at a price you cannot pay for long. Plus where a mirror sits, what that means it cannot show you, and the half of a conversation people lose without noticing.
network-plusnetworkingmonitoring40Baselines, alerting and monitoring solutions
Why a number on its own is not evidence of anything, what a threshold does to a metric that has a daily shape, and the two ways a counter lies to the system reading it.
network-plusnetworkingmonitoring41Disaster recovery
Two objectives measured from the same moment in opposite directions, three kinds of standby site that differ only in what is already switched on, and the failover step nobody has ever run with users on it.
network-plusnetworkingoperations42DHCP
Four messages, two of them shouted by a machine with no address. Plus what a reservation is not, the three deadlines inside a lease, and the one field that lets a server hand out addresses on a subnet it has never seen.
network-plusnetworkingservices43IPv6 address assignment and SLAAC
How a host ends up with three IPv6 addresses nobody configured, the two flag bits in a router advertisement that decide whether DHCPv6 is involved at all, and what happens when two machines claim the same address.
network-plusnetworkingservices44How DNS resolution works
The walk from the root down, drawn and then captured on a lab with its own root server. Plus the one flag that separates an answer from a copy of an answer, and why a change you made this morning is still invisible this afternoon.
network-plusnetworkingservices45What happens when you open a web page
One capture of one page load, from the first frame to the last, with every step named and tied to its layer. Nine things happen in twelve milliseconds and any one of them failing produces the same sentence from the user.
network-plusnetworkingfundamentals46DNS records and zones
A record type is a question type, which is why moving a website and moving the mail are separate jobs. Plus the five numbers in the SOA, what a zone actually is, and the one place a CNAME is not allowed.
network-plusnetworkingservices47DNS security
A signed answer proves the zone owner wrote it and hides nothing. An encrypted one hides the question and proves nothing about the answer. Both, demonstrated on a lab that signs its own zone and then breaks it.
network-plusnetworkingsecurity48Time protocols
Stratum counts hops rather than quality, a clock that is wrong makes a perfectly good certificate look forged, and the fault presents as a security problem on exactly one machine.
network-plusnetworkingservices49IP protocols and tunnelling
The field in the IP header that says what the payload is, and what happens when the answer is another packet. GRE and IPSec captured from the middle, where one of them shows you everything.
network-plusnetworkingfundamentals50VPNs
Where the tunnel ends decides everything else. Site to site against client to site, clientless access, and why split tunnel is an argument about policy rather than a setting.
network-plusnetworkingsecurity51Managing devices remotely
Four ways in, and the one that still works when the network does not. Plus a jump box that refuses to route, and a device locked out by a single command sent over the connection it broke.
network-plusnetworkingoperations52Physical security and deception
Cameras, locks and badge readers as network controls rather than building ones, why the most effective attack on a data centre needs no exploit at all, and what a honeypot is actually for, which is not catching anybody.
network-plusnetworkingsecuritybeginner53Compliance and audits
Why a payment standard and a data protection regulation reach all the way down to how you wire a network, what data locality actually constrains, and why an audit asks you to prove a control works rather than that it exists.
network-plusnetworkingsecuritycompliance54Access lists, filtering and security zones
The rule is in the list and traffic still gets through. How a list is evaluated, why order decides everything, what the implicit deny at the bottom is doing, and what a trusted zone actually means once you stop assuming it.
network-plusnetworkingsecurityfiltering55Network segmentation
A vending machine on the same network as the payment system. What segmentation actually enforces, which devices need a segment of their own, and why a guest network is a segmentation decision rather than a wireless one.
network-plusnetworkingsecuritysegmentation56Layer 2 attacks
Everything still works and somebody is reading all of it. MAC flooding that turns a switch back into a hub, ARP poisoning that puts an attacker in the middle, and VLAN hopping that crosses a boundary the tagging was supposed to hold, each one captured.
network-plusnetworkingsecurityattacks57Attacks on services and people
The network is fine and the company has been compromised. Denial of service and the amplification that makes it cheap, the rogue services that answer before the real one does, the evil twin, and the human techniques that are on a network exam for a reason.
network-plusnetworkingsecurityattacks58Device hardening and network access control
A switch in a meeting room with sixteen live ports. The cheap controls that close most of the door, why MAC filtering is a speed bump you can watch an attacker step over, and 802.1X, where a port passes nothing but the authentication until the authentication succeeds.
network-plusnetworkingsecurityaccess-control59Cloud concepts and connectivity
The server is in a building you will never visit. Service and deployment models without the marketing, what a virtual private cloud actually is, why a security group is not a firewall appliance, and the two ways to connect your network to a cloud.
network-plusnetworkingcloud60Zero trust, SASE and infrastructure as code
The old model trusted anything already inside the building. Zero trust checks every request wherever it comes from, SASE moves the controls to where the users are, and infrastructure as code makes the network a repository you can catch drifting from its source.
network-plusnetworkingsecuritymodern61The troubleshooting methodology
Everything is broken and you have to start somewhere. CompTIA's seven steps in order, what each one is actually guarding against, why testing the theory can send you back a step, and why the step everyone skips is the one that pays next time.
network-plusnetworkingtroubleshootingmethodology62Ping, traceroute and what they prove
Ping fails and the server is serving traffic perfectly. What an echo actually tests and what it does not, how traceroute finds each hop by letting a packet die there, why loss at a hop is not loss to the end, and why a failed test proves far less than a successful one.
network-plusnetworkingtroubleshootingtools63Connection and interface tools
Something is listening on a port and nobody knows what. Listing listening sockets and reading the address each is bound to, seeing who is connected right now, the interface tools on each platform and which name goes with which, and the neighbour table.
network-plusnetworkingtroubleshootingtools64Name resolution tools
The name resolves on your machine and not on theirs. Querying a specific server instead of the default one, reading an answer section, telling an authoritative answer from a cached copy by one flag, and doing forward and reverse lookups with the tool the exam names.
network-plusnetworkingtroubleshootingtools65Narrowing a fault by layer
Fifteen candidates, two machines, and one afternoon. Top-down, bottom-up and divide-and-conquer as three named ways to search the stack, why the discriminating test is the only real unit of progress, and why one test in the middle beats ten in a row.
network-plusnetworkingtroubleshootingmethodology66Cable faults and signal problems
The link works at 100 Mb and refuses to negotiate 1000. Which faults a continuity tester finds and which it cannot see, why attenuation, crosstalk and interference each leave a different fingerprint, and why the speed a link settles at is the cheapest diagnostic you own.
network-plusnetworkingtroubleshootingcabling67Interface counters and port status
The interface is up and the counters are climbing. Why an error and a drop are different sentences about a frame, what each counter narrows the fault to, why a number is worthless until you read it twice, and how to tell a port that was switched off from one with nothing on the end of it.
network-plusnetworkingtroubleshootinginterfaces68PoE and transceiver problems
Six cameras, one switch, and the sixth one keeps rebooting. Why a power budget is a total rather than a per-port limit, what happens when an injector and a device disagree about the standard, and how a switch tells you a fibre link is dim rather than broken.
network-plusnetworkingtroubleshootingpoe69Switching faults, loops and VLANs
The network is saturated and no host is sending anything. What one extra cable does to a switched network in a second, why the root bridge election decides every path in the network, and why a VLAN fault looks exactly like a broken host.
network-plusnetworkingtroubleshootingswitching70Routing and default gateway faults
Local traffic is perfect and nothing leaves the building. How the error message tells you how far the packet got, why a missing route and a wrong gateway fail differently, and why traffic taking a path nobody expected is usually one line somebody left behind.
network-plusnetworkingtroubleshootingrouting71Addressing faults
Two machines, one address, and connectivity that comes and goes. Why a duplicate address produces intermittent failure rather than an error, why a wrong mask fails one way down the wire and looks like broken hardware, and why an empty DHCP pool looks identical to four other faults from the client.
network-plusnetworkingtroubleshootingaddressing72Wireless performance and roaming
Full signal strength, and the connection keeps dropping. Why airtime rather than bandwidth is what a cell shares, why one distant laptop slows a whole room, how a coverage gap and a capacity problem produce identical complaints with opposite fixes, and the channel change nobody made.
network-plusnetworkingtroubleshootingwireless73Packet capture and protocol analysis
The two teams disagree and the packets settle it. The two decisions to make before you start a capture, why a reset and a silence mean opposite things, how two captures at two points name the device that is dropping traffic, and what a capture of nothing still proves.
network-plusnetworkingtroubleshootingtools74Discovery tools and device commands
You inherit a network and no documentation. Finding what is on a segment and what it is running, getting the devices to describe each other so a diagram builds itself, the four questions a device command answers, and why scanning is a permission question before it is a technical one.
network-plusnetworkingtroubleshootingtools75Bandwidth, congestion and bottlenecks
The link is at 40 percent and everything is slow. Why a five minute average hides a link that was completely full, why contention shares a link rather than slowing it, and why one bulk transfer punishes every other user on the path.
network-plusnetworkingtroubleshootingperformance76Latency, jitter and packet loss
The call breaks up and the file transfer is fine. Why a packet that arrives late is a packet that is lost when something is waiting for it, why one percent loss costs a TCP transfer most of its speed, and why the same path can be excellent and unusable at the same time.
network-plusnetworkingtroubleshootingperformance
Beyond the exam
Not tested, and no practice question points at any of it. These are the things the certification leaves out that you will want on the job.
Quality of service
The call breaks up every afternoon and the link is not full for the other twenty-three hours. What a marking is, where the queue that acts on it lives, the difference between shaping and policing, and why your marks stop meaning anything the moment traffic leaves your estate.
network-plusnetworkingperformancebeyond-the-examWi-Fi generations and the number on the box
The exam names no 802.11 letter, so this track never did either. Which amendment each marketing generation maps to, what actually changed at each step, how to take apart the throughput figure on a datasheet, and why the generation that matters is the one your clients have.
network-plusnetworkingwirelessbeyond-the-examHow the internet is glued together
Your router knows how to reach a server in Tokyo and nobody told it. Autonomous systems, the three relationships every network has with its neighbours, why an announcement is a claim rather than a fact, and what the signing system built to check those claims does and does not cover.
network-plusnetworkingroutingsecuritybeyond-the-examReading the standards
Every page of this track ends in a list of documents and one of its three forms of evidence is to go and read a named clause. Which document is current, what its status actually means, why MUST and SHOULD are the two most expensive words in networking, and how to get at the ones behind a paywall.
network-plusnetworkingstandardsbeyond-the-examThe hour after it breaks
Topic 61 gives you a method for finding a fault. This is everything happening around you while you use it: who runs the incident, what to say when you do not know yet, when escalating is the right call, and why a postmortem that names a person has found nothing.
network-plusnetworkingoperationsbeyond-the-examHow big networks actually break
Three of the largest failures of recent years, read as faults rather than as news. A backbone that withdrew itself from the internet, a DNS record that automation emptied, and a filter deleted during a tidy-up. All three organisations employ excellent engineers, and none of the causes are exotic.
network-plusnetworkingoperationsbeyond-the-exam