CompTIA Network+ (N10-009) Cheatsheet — High-Yield Tables, Diagrams & Commands

Fast recall for N10-009: OSI model, subnetting, IPv6 essentials, VLANs/trunks, Wi‑Fi, cabling/fiber, ports/protocols, DHCP/DNS, VPN/AAA, and a troubleshooting playbook with common commands.

On this page

Use this for last-mile review. Star weak rows and re-drill with practice.

1) OSI model (memorize + use for troubleshooting)

Layer	Name	PDU	Common examples
7	Application	Data	HTTP/S, DNS, SMTP, DHCP (conceptual)
6	Presentation	Data	TLS/SSL, encoding, compression
5	Session	Data	Session setup/teardown (high level)
4	Transport	Segment/Datagram	TCP/UDP, ports
3	Network	Packet	IP, routing, ICMP
2	Data Link	Frame	Ethernet, VLANs, MAC, ARP
1	Physical	Bits	Cabling, RF, signaling

    flowchart LR
	  A[App data] --> B[TCP/UDP + ports]
	  B --> C[IP + routing]
	  C --> D[Ethernet + MAC/VLAN]
	  D --> E[Bits on wire / RF]

2) IPv4 subnetting quick table

Rules

Hosts per subnet = 2^(host bits) - 2 (except /31 point-to-point)
Block size = 256 - mask_octet (in the interesting octet)

Prefix	Mask	Usable hosts	Block size (last octet)
/24	255.255.255.0	254	1
/25	255.255.255.128	126	128
/26	255.255.255.192	62	64
/27	255.255.255.224	30	32
/28	255.255.255.240	14	16
/29	255.255.255.248	6	8
/30	255.255.255.252	2	4
/31	255.255.255.254	2 (P2P)	2

Fast sanity checks

Same subnet? Compare each IP to the mask (or compute the network address).
Default gateway must be in the same subnet as the host.

3) IPv6 essentials

Address types
- Global unicast: 2000::/3 (public)
- Unique local (ULA): fc00::/7 (private-ish)
- Link-local: fe80::/10 (always on; neighbor discovery)
Compression: remove leading zeros; :: only once per address.
Common multicast
- ff02::1 all nodes (local link)
- ff02::2 all routers (local link)
- ff02::1:ff00:0/104 solicited-node (ND)

4) VLANs, trunks, and switching basics

Access port: untagged, belongs to one VLAN.
Trunk port (802.1Q): tagged, carries multiple VLANs between switches/APs/routers.
Native VLAN: untagged VLAN on a trunk (avoid misuse; document it).
STP: prevents loops; a loop often shows as broadcast storms and MAC flapping.

5) Wi‑Fi quick table + security

Generation	IEEE	Bands	Notes
Wi‑Fi 4	802.11n	2.4/5	MIMO
Wi‑Fi 5	802.11ac	5	MU‑MIMO, wider channels
Wi‑Fi 6/6E	802.11ax	2.4/5/6	OFDMA, dense environments

Channel planning

2.4 GHz: prefer 1 / 6 / 11 to avoid overlap.

Security order (best → worst)

WPA3 → WPA2 (AES/CCMP) → WPA (TKIP) → WEP (avoid)
Enterprise auth: 802.1X with RADIUS + EAP (scenario picks often favor this).

6) Cabling, fiber, optics, and PoE

Copper

Cable	Typical use	Notes
Cat5e	1 Gbps @ 100 m	Common baseline
Cat6	10 Gbps @ ~55 m	Better noise performance
Cat6a	10 Gbps @ 100 m	Best pick for long 10G copper runs

Fiber

Fiber	Mode	Typical range	Notes
MMF	Multi‑mode	Short	Common in buildings
SMF	Single‑mode	Long	Metro/long distance

Transceivers

SFP (1G), SFP+ (10G), QSFP (40G/100G variants)

PoE

802.3af (PoE) • 802.3at (PoE+) • 802.3bt (PoE++)
Know that higher PoE classes power APs, cameras, and phones.

7) Ports & protocols (high yield)

Service	Port/Proto	Notes
DNS	53 UDP/TCP	UDP for queries; TCP for zone/large replies
DHCP	67/68 UDP	Server/client
HTTP / HTTPS	80 / 443 TCP	Web; TLS on 443
SSH	22 TCP	Secure remote management
Telnet	23 TCP	Insecure (distractor)
RDP	3389 TCP/UDP	Remote desktop
SMB	445 TCP	Windows file sharing
NTP	123 UDP	Time sync
SNMP	161/162 UDP	Polling / traps
Syslog	514 UDP	Logging (TCP variants exist)
LDAP / LDAPS	389 / 636 TCP	Directory
RADIUS	1812/1813 UDP	AAA (auth/accounting)
TACACS+	49 TCP	AAA (common alt)

8) DHCP & DNS quick picks

DHCP DORA Discover → Offer → Request → Acknowledge

DNS records

A / AAAA (name → IP)
CNAME (alias)
MX (mail)
TXT (verification/SPF hints)
PTR (reverse lookup)

9) VPN + AAA at a glance

Site-to-site VPN: typically IPsec tunnel between gateways.
Remote access VPN: user → gateway; often SSL/TLS-based or IPsec.
AAA: central auth and auditing; common pattern is RADIUS/TACACS+ plus MFA.

10) Troubleshooting playbook (symptom → layer → tools)

Symptom	Likely layer	Fast checks / tools
No link light	L1	Cable, port, PoE, NIC enabled
APIPA (`169.254.x.x`)	L3/service	DHCP scope, VLAN, relay, server reachability
IP works, names fail	L7/service	DNS servers, `nslookup`/`dig`, firewall 53
One VLAN can’t reach gateway	L2/L3	VLAN on access port, trunk allowed VLANs, SVI/gateway
High latency/packet loss	L3/L4	`ping`, `tracert/traceroute`, interface errors, congestion
Intermittent drops	L1/L2	Duplex/speed mismatch, bad cable, loops/STP, Wi‑Fi interference

Useful commands

 1# Windows
 2ipconfig /all
 3ping 8.8.8.8
 4tracert example.com
 5nslookup example.com
 6
 7# Linux/macOS
 8ip a
 9ip route
10traceroute example.com
11dig example.com
12sudo tcpdump -ni any port 53

Wireshark filter starters

dns
tcp.port == 443
ip.addr == 10.0.0.10

Next steps

Syllabus: objectives by domain → Open
Practice: drills + mocks → Start

Syllabus

Practice

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