Introduction to the Internet Protocol

CompTIA Network+ · N10-009 · Objectives 1.1 & 1.4

Chapter 6 — Introduction to the Internet Protocol

Four TCP/IP layers, thousands of ports, and one end-to-end journey. This study map connects protocols to ports, TCP and UDP to their behavior, IP to routing, ARP to local delivery, and GRE/IPSec to secure tunneling.

15 sectionsPort explorerTCP handshakeDORA simulatorEncapsulation builder15-question exam check

Backbone / Contents

01

TCP/IP and OSI Mapping

TCP/IP is the open protocol suite used by the Internet and most private networks. Its four layers combine the seven OSI layers into a practical implementation model.

TCP/IP layer	OSI equivalent	Primary responsibility
Process/Application	7, 6, 5	Application services, representation, and sessions
Host-to-Host	4 Transport	End-to-end delivery, reliability, and ports
Internet	3 Network	Logical addressing, routing, and packets
Network Access	2 and 1	Frames, MAC addresses, media, and signals

Mapping ruleHost-to-Host = Transport. Internet = Network. Process/Application combines OSI 5–7. Network Access combines OSI 1–2.

02

Protocol & Port Explorer

Select a protocol to connect its port, transport, purpose, and security clue.

03

Secure Replacement Flip Cards

Flip each older service to reveal the secure exam choice.

Telnet · TCP 23

Secure terminal?

SSH · TCP 22. Encrypts authentication and terminal traffic.

FTP · TCP 20/21

Secure file transfer?

SFTP · TCP 22. Transfers files through SSH; it is not FTP with TLS.

HTTP · TCP 80

Secure web?

HTTPS · TCP 443. Protects browser-server traffic with TLS.

LDAP · TCP 389

Secure directory?

LDAPS · TCP 636. Encrypts directory queries and credentials.

SMTP · TCP 25

Secure submission?

Submission · TCP 587. TLS protects submitted email in transit.

Exam trapSFTP is a separate SSH-based service on TCP 22—not “FTP with TLS.”

04

DHCP DORA & APIPA

DHCP uses UDP 67 on the server and UDP 68 on the client to deliver addressing, gateway, DNS, and domain information.

Client starts at 0.0.0.0 and broadcasts DHCPDISCOVER.

APIPA clueAn unexpected 169.254.x.x address means the Windows client could not reach DHCP or receive a valid lease.

05

Monitoring, Logging & Time

Syslog level	Severity	Meaning
0	Emergency	System unusable
1–3	Alert–Error	Immediate or serious condition
4–5	Warning–Notice	Potential problem or notable event
6–7	Information–Debug	Normal detail or diagnostics

Severity ruleLower syslog number means greater severity: 0 is Emergency; 7 is Debugging.

06

TCP versus UDP

Connection-oriented

TCP

Virtual circuit, sequencing, acknowledgments, retransmission, windowing, and higher overhead.

Connectionless

UDP

No built-in delivery guarantee, order, or flow control; low overhead and fast delivery.

Best fit

Reliability vs. speed

TCP suits web, email, files, and remote access. UDP suits voice, video, simple queries, monitoring, and broadcasts.

Important“Unreliable” does not mean bad. UDP deliberately omits recovery features when speed matters or reliability is handled elsewhere.

07

TCP Session Animator

A TCP connection starts by synchronizing sequence numbers. Step through SYN, SYN/ACK, and ACK.

No virtual circuit yet.

08

TCP Header & Flags

Flag	Meaning	Exam clue
SYN	Synchronize sequence numbers	Starts connection
ACK	Acknowledgment field valid	Confirms received data
FIN	Graceful finish	Normal close
RST	Immediate reset	Abort or reject
PSH	Push promptly	Deliver to application now
URG	Urgent pointer valid	Urgent data

09

Internet Protocol, TTL & MTU

IP provides logical addressing and routing on a best-effort basis. It does not guarantee delivery, order, or recovery.

Loop prevention

TTL

Each router decrements Time to Live. A packet is discarded when TTL reaches zero.

Packet size

MTU

Largest Layer 3 packet a link carries without fragmentation. Path-MTU problems may break large transfers while small packets work.

Next payload

Protocol field

Identifies ICMP 1, TCP 6, UDP 17, GRE 47, or another protocol carried inside IPv4.

Exam trapPorts identify applications inside TCP or UDP. The IPv4 Protocol field identifies the carried protocol. TCP is protocol 6—not “port 6.”

10

IP Protocol Number Explorer

11

ICMP & ARP

Control and errors

ICMP

Ping uses Echo Request/Reply. Tracert uses TTL expiry and Time Exceeded. A blocked ping alone does not prove a host is down.

IPv4 to local MAC

ARP

Checks cache, broadcasts a request on the local link, and learns the owner’s MAC address.

ARP decision lab

A client at 192.168.10.25/24 sends data to 198.51.100.20. Whose MAC address must it resolve?

Choose one answer.

Core ruleFor a remote destination, ARP resolves the local default gateway’s MAC. The IP destination remains the remote host.

12

GRE & IPSec

Flexible tunnel

GRE

Carries multiple Layer 3 protocols and multicast, but provides no encryption, authentication, or confidentiality.

Authenticate

AH

Provides origin authentication and integrity, but no encryption; address changes such as NAT are problematic.

Encrypt

ESP

Provides confidentiality plus optional integrity, authentication, and anti-replay protection.

Negotiate

IKE

Negotiates peers, security associations, algorithms, parameters, and keys.

Memory hookAH authenticates. ESP encrypts and can authenticate. IKE negotiates. GRE gains security when protected by IPSec.

13

Encapsulation Builder

Build the sending sequence from application data to physical bits.

Start with application data.

OrderData → Segment/Datagram → Packet → Frame → Bits. Receiving devices reverse the process.

14

PowerShell 7 Practice

Get-NetTCPConnectionTCP listeners and connections

Get-NetUDPEndpointLocal UDP endpoints

Test-NetConnection example.com -Port 443DNS and TCP port test

Get-NetNeighborARP / neighbor cache

Get-NetRouteLocal routing table

ping example.comICMP Echo test

tracert example.comTTL-based routed path

ipconfig /allDHCP, DNS, and addressing

15

Exam Check

Fifteen questions drawn directly from the Chapter 6 manual.

Score: 0 / 0

NETWORK+ STUDY MAP · CHAPTER 6 · INTRODUCTION TO THE INTERNET PROTOCOL