Network + Comprehensive Review

Layer 1 Physical

Cabling, radio, light, pinouts, transceivers, signal quality, speed/duplex negotiation.

Layer 2 Data Link

Ethernet frames, MAC addresses, switching, VLAN tags, ARP adjacency, STP

Layer 3 Network

IP addressing, routing, ICMP, IPv4/IPv6 packet delivery between networks

Layer 4 Transport

TCP/UDP ports, segmentation, reliability, retransmission, sequencing, and flow control

Layer 5 Session

Setup, maintain, and tear down conversations

Layer 6 Presentation

Encryption, compression, and data formatting

Layer 7 Application

User-facing network services such as DNS, HTTP, HTTPS, SMTP, SSH clients, and directory queries.

Destination MAC

Tells which local NIC should receive the frame

Source MAC

Tells who sent the frame on the local segment

EtherType

Identifies payload type such as IPv4 or IPv6

SaaS

Provider manages application and infrastructure. Customer mainly manages data and identities

PaaS

Provider manages infrastructure, OS, runtime. Customer manages application and data

IaaS

Provider manages physical infrastructure. Customer manages OS, applications, data, and much network security policy

Unicast

One sender to one receiver. Most web traffic is unicast.

Broadcast

One sender to all devices in the broadcast domain

Multicast

One sender to interested receivers. Often used for streaming.

Anycast

Many destinations share one address; routing sends clients to the nearest/best instance. Common for DNS and CDNs.

Private IPv4 Ranges:

10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16

APIPA

169.254.0.0/16. This means DHCP failed or no static address was configured

Port 20/21

FTP

File Transfer, not secure

Port 22

SSH

Secure File transfer via SSH

Port 23

Telnet

Insecure remote CLi

Port 25

SMTP

Mail transfer between servers

Port 53

DNS

Port 67/68

DHCP

Server: 67

Client: 68

Port 80

HTTP

Unencrypted Web

Port 110

POP3

Download Email

Port 143

IMAP

Mailbox Sync between devices

Port 389

LDAP

Directory Queries

Port 443

HTTPS

Encrypted web using TLS

Port 445

SMB

Windows File/Printer Sharing

Port 3389

RDP

Remote Desktop

802.11a

5GHz

Legacy

802.11b

2.4 Hz

Legacy

802.11g

2.4 GHz

Legacy

Better than 802.11b

802.11n

2.4/5 GHz

Wi-Fi 4

802.11ac

5 GHz

Wi-Fi 5

802.11ax

2.4/5 GHz

Wi-Fi 6

WEP

Broken

Weak RC4/IV design

WPA

Legacy

Better than WEP, but outdated

WPA2-Personal

Common

PSK with AES/CCMP

Strong if passphrase is strong

WPA2-Enterprise

Business

802.1X/EAP/RADIUS.

Per-User Auth

WPA3-Personal

Best Personal

SAE improves resistance to offline dictionary attacks

WPA3-Enterprise

Best Enterprise

Stronger enterprise security options

Certificate based EAP-TLS

RIP

Routing protocol

Uses Hops (Max count 15)

OSPS (Open Shortest Path First)

Uses Cost instead of Hops (Bandwidth)

Chooses the route based off of speed, not how many hops

EIGRP (Enhanced Interior Gateway Routing Protocol)

Less universal

Most common in Cisco environments

BGP (Border Gateway Protocol)

Directs traffic across the internet

Functions like a postal service by choosing the most efficient path for data to travel between separate networks (Autonomous Systems) worldwide.

Trunk Port

Carries traffic for multiple VLANs across a single cable

Access Port

Carries traffic for one VLAN

Used for connecting end user devices to a switch

MTTR

Mean time to repair (Average time)

MTBF

Mean time between failures

Confidentiality

Prevent unauthorized disclosure

Encryption/Access Control

Availiability

Keep Services reachable

Redundancy, DDoS protection, etc

Integrity

Prevent unauthorized modification

Hashing, checksums, etc

AAA

Authentication: Who are you?

Authorization: What are you allowed to do?

Accounting: What did you do?

RADIUS

Encrypts the password, not the whole packet

TACACS+

Encrypts the entire packet body

Preferred for network device administration

Kerberos

Uses tickets, supports SSO

Depends heavily on synchronized time

EAP-TLS

Password-less authentication protocol for Wireless networks

Uses certificates

Distance-Vector Protocol

Routers share their entire routing table with neighbors at regular intervals

Metrics: Hop Count

Link-State Protocol

Routers share information about the state of their links with all routers in the network

Metrics: Cost (bandwidth)

Path-Vector Protocols

Used for routing between autonomous systems

Metrics: Path Attributes (length)

Autonomous Systems

A collection of IP networks under a single administrative domain

Spanning Tree Protocol

• Prevents network loops by creating a loop free logical topology at layer 2

• Assigns specific roles to switch ports to maintain a loop-free network

Network Loops

Occurs when multiple active paths exist between network switches, causing network congestion