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Cisco CCNA 200-301 Study Notes

OSI and TCP/IP Reference Models

Foundational models for network communication

OSI Model (7 Layers)

Layer	Name	PDU	Key Protocols
7	Application	Data	HTTP, HTTPS, DNS, DHCP, FTP, SMTP
6	Presentation	Data	TLS/SSL, JPEG, ASCII
5	Session	Data	NetBIOS, RPC
4	Transport	Segment	TCP, UDP
3	Network	Packet	IP, ICMP, OSPF
2	Data Link	Frame	Ethernet, 802.1Q, STP
1	Physical	Bits	Cables, Hubs, Signals

TCP vs UDP

TCP

Connection-oriented, reliable, ordered delivery. Uses 3-way handshake (SYN, SYN-ACK, ACK). Used by HTTP, FTP, SSH.

UDP

Connectionless, fast, no delivery guarantee. Used by DNS, DHCP, TFTP, VoIP, video streaming.

Common Port Numbers

20/21: FTP | 22: SSH/SFTP | 23: Telnet | 25: SMTP
53: DNS | 67/68: DHCP | 69: TFTP | 80: HTTP
110: POP3 | 143: IMAP | 161/162: SNMP | 443: HTTPS
514: Syslog | 830: NETCONF | 8080: HTTP Alternate

Exam Focus Areas

TCP uses 3-way handshake – SYN, SYN-ACK, ACK
UDP is used where speed > reliability (DHCP, DNS, TFTP)
Memorize well-known ports 0-1023
IPv4 header = 20 bytes minimum; IPv6 header = 40 bytes fixed

IPv4 Addressing and Subnetting

IPv4 address classes, CIDR, and subnetting

IPv4 Address Classes

Class	Range	Default Mask	Use
A	1.0.0.0 – 126.255.255.255	/8 (255.0.0.0)	Large networks
B	128.0.0.0 – 191.255.255.255	/16 (255.255.0.0)	Medium networks
C	192.0.0.0 – 223.255.255.255	/24 (255.255.255.0)	Small networks
D	224.0.0.0 – 239.255.255.255	N/A	Multicast
E	240.0.0.0 – 255.255.255.255	N/A	Reserved/Experimental

Private Address Ranges (RFC 1918)

10.0.0.0/8 — Class A private (10.0.0.0 – 10.255.255.255)
172.16.0.0/12 — Class B private (172.16.0.0 – 172.31.255.255)
192.168.0.0/16 — Class C private (192.168.0.0 – 192.168.255.255)

Subnetting Key Formula

Subnets = 2^(borrowed bits) | Hosts = 2^(host bits) – 2
/30 = 255.255.255.252 → 4 addresses, 2 usable (point-to-point links)
/29 = 255.255.255.248 → 8 addresses, 6 usable
Broadcast = last address in subnet; Network = first address

Exam Focus Areas

127.0.0.0/8 is loopback (localhost = 127.0.0.1)
169.254.x.x is APIPA (link-local) — no DHCP response
/32 = single host route; /31 = point-to-point (RFC 3021)
VLSM allows different subnet masks within same network

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Cisco CCNA 200-301 Study Notes

OSI and TCP/IP Reference Models

Foundational models for network communication

OSI Model (7 Layers)

Layer	Name	PDU	Key Protocols
7	Application	Data	HTTP, HTTPS, DNS, DHCP, FTP, SMTP
6	Presentation	Data	TLS/SSL, JPEG, ASCII
5	Session	Data	NetBIOS, RPC
4	Transport	Segment	TCP, UDP
3	Network	Packet	IP, ICMP, OSPF
2	Data Link	Frame	Ethernet, 802.1Q, STP
1	Physical	Bits	Cables, Hubs, Signals

TCP vs UDP

TCP

Connection-oriented, reliable, ordered delivery. Uses 3-way handshake (SYN, SYN-ACK, ACK). Used by HTTP, FTP, SSH.

UDP

Connectionless, fast, no delivery guarantee. Used by DNS, DHCP, TFTP, VoIP, video streaming.

Common Port Numbers

20/21: FTP | 22: SSH/SFTP | 23: Telnet | 25: SMTP
53: DNS | 67/68: DHCP | 69: TFTP | 80: HTTP
110: POP3 | 143: IMAP | 161/162: SNMP | 443: HTTPS
514: Syslog | 830: NETCONF | 8080: HTTP Alternate

Exam Focus Areas

TCP uses 3-way handshake – SYN, SYN-ACK, ACK
UDP is used where speed > reliability (DHCP, DNS, TFTP)
Memorize well-known ports 0-1023
IPv4 header = 20 bytes minimum; IPv6 header = 40 bytes fixed

IPv4 Addressing and Subnetting

IPv4 address classes, CIDR, and subnetting

IPv4 Address Classes

Class	Range	Default Mask	Use
A	1.0.0.0 – 126.255.255.255	/8 (255.0.0.0)	Large networks
B	128.0.0.0 – 191.255.255.255	/16 (255.255.0.0)	Medium networks
C	192.0.0.0 – 223.255.255.255	/24 (255.255.255.0)	Small networks
D	224.0.0.0 – 239.255.255.255	N/A	Multicast
E	240.0.0.0 – 255.255.255.255	N/A	Reserved/Experimental

Private Address Ranges (RFC 1918)

10.0.0.0/8 — Class A private (10.0.0.0 – 10.255.255.255)
172.16.0.0/12 — Class B private (172.16.0.0 – 172.31.255.255)
192.168.0.0/16 — Class C private (192.168.0.0 – 192.168.255.255)

Subnetting Key Formula

Subnets = 2^(borrowed bits) | Hosts = 2^(host bits) – 2
/30 = 255.255.255.252 → 4 addresses, 2 usable (point-to-point links)
/29 = 255.255.255.248 → 8 addresses, 6 usable
Broadcast = last address in subnet; Network = first address

Exam Focus Areas

127.0.0.0/8 is loopback (localhost = 127.0.0.1)
169.254.x.x is APIPA (link-local) — no DHCP response
/32 = single host route; /31 = point-to-point (RFC 3021)
VLSM allows different subnet masks within same network

Read cisco-ccna notes without distractions

Open Foci to run a focused study block while you review domains, tables, and exam tips.

Focus while reading