Computer Networking Final

Layer 2 - Data Link

Handles MAC addressing and switching; devices: switch, NIC (Network Interface Card)

Layer 3 - Network

Handles IP addressing and routing; devices: router

Layer 4 - Transport

Provides end-to-end communication using TCP and UDP with ports

Layer 7 - Application

Closest to the user; includes HTTP, DNS, FTP, email protocols

OSI Acronym

A Pussy So Tight No Dick Penetrates

OSI Model

Layered framework for how data is transmitted across netoworks

TCP

Reliable, connection-oriented protocol using a 3-way handshake (SYN, SYN-ACK, ACK)

UDP

Fast, connectionless protocol with no guarantees of delivery or ordering.

Fields that define a TCP or UDP connection (5 tuple)

Protocol, Local IP, Local Port, Remote IP, Remote Port

Routing Table Purpose

Lists networks the router can reach; their netmasks, next hop, and interface to use.

Routing Interface Requirement

A router must have an interface in every network it connects to.

Routing Table Match Rule

IP addresses is matched against the network and netmask entries in the table.

Routing Behavior

Each router makes independent decisions based on its own configuration and view of the network.

Netmask Function

Used to determine how much of the IP address refers to the network vs host portion

LAN (Local Area Network)

A broadcast domain where all devices can directly communicate with a router

Broadcast Packet (on Ethernet LAN)

Sent to all of devices on the same LAN segment

Do LANs cross routers?

No, routers separate LANs into different broadcast domains

Switch Behavior

Learns MAC addresses and floods frames if the destination MAC is unknown

How to build a bigger LAN

Plug multiple switches together; no additional config required

How to create smaller broadcast domains

Use VLANs to subdivide a switch into logical LANs

VLAN

A logical partition within a switch that separates traffic into isolated broadcast domains

Access Port Behavior

Assigns frames to a VLAN based on the port the traffic enters; does not use tags

Trunk Port Behavior

Adds a VLAN tag to frames to allow traffic for multiple VLANs over a single link.

Routing Between VLANs (with router)

Requires traffic to exit the switch to a router and return

Layer 3 Switch Function

A switch that can route traffic between VLANs internally without a separate router

WiFi and Ethernet Similarity

Use MAC addresses and ARP in the same way

WiFi Physical Differences

Uses radio frequencies (2.4GHz, 5GHz), not copper or fiber

WiFi and Ethernet Similarities

Use MAC addresses and ARP in the same way

WiFi Error Rate

Higher than ethernet; can be 10% more due to interference

SSID

The name of a WiFi network; advertised by access points using beacon frames

Beacon Frame

Signal sent by a client device to ask what networks are available

WPA2

Preferred wireless security protocol that uses AES encryption

WEP

Outdated and insecure encryption method for WiFi; should not be used

NAT (Network Address Translation)

Translates internal private IP addresses to a public IP so devices can access the internet

Purpose of NAT

To conserve IPv4 addresses and allow multiple devices to share one public IP

NAT table

Tracks which internal IP and port maps to which external IP and port

NAT table fields

Includes internal IP, internal port, external IP, and external port

Static NAT entry

A fixed rule that maps a specific internal IP and port to a public IP and port; used to host services

Ephemeral Port

A randomly assigned port above 1023 used by client devices when communicating with servers

Public IP Address

An IP address that can be routed over the internet and must be globally unique

Private IP address

IP address reserved for internal use (e.g., 192.168.x.x); not routable over the internet

Why is duplicate destination address a NAT problem?

The router can’t tell which internal device should receive the response.

HTTP (Hypertext Transfer Protocol)

A request/response protocol used to load web pages

HTTP POST Method

Sends data to a server to modify or update resources

HTTP GET Method

Requests data from a server without modifying anything

HTTP Status Code 200

Ok, the request was successful

HTTP Status Code 404

Not found, the server could not find the requested resource

HTTP Status Code 500

Server Error, something went wrong on the server side

HTTPS (HTTP Secure)

Uses TLS encryption to protect HTTP traffic; runs on port 443

TLS (Transport Layer Security)

Protocol that encrypts web traffic and replaces SSL

Cookie (In HTTP)

Small piece of data stored by the browser to track sessions in between requests

Layer 2 Address

MAC address; used to deliver frames with the same local network

Layer 3 Address

IP address; used to deliver packets between network

Layer 4 Address

Port number, used to identify applications or services on a device

Layer 7 Address

URL or email address; used by end-user applications

Traceroute

A tool that shows the path (hops) packets take from your device to a destination

CDN (Content Delivery Network)

A system of distributed servers that cache content closer to users for faster delivery

DNS (Domain Name System)

Translates human-readable domain names (like google.com) into IP addresses

Purpose of a netmask?

Separates IP address into network and host parts.

What portion of the IP address is identified by the netmask?

The network portion.

Default route IP/netmask notation?

0.0.0.0/0

Which route is chosen if multiple match an IP destination?

The route with the longest (most specific) prefix.

What is a default gateway?

The route used when no other routing table entry matches.

Routing decision: IP 10.0.2.5, routes available 10.0.0.0/8 and 10.0.2.0/24, which is selected?

10.0.2.0/24 because its more specific

Which netmask example has a larger range but less specific? /8 or /24 ; Less range but more specific?

/8, /24

What type of NAT entry must be manually configured to host a server behind NAT?

Static NAT entry

What does a NAT server do with outgoing packets from a private network?

It translates the private IP/port to a public IP/port

Key differences between distance vector and link-state protocols?

Distance Vector is slower and has neighbor-based updates while Link-State is faster with topology-wide updates,

Is OSPF interior or exterior routing protocol?

Interior (IGP)

Is BGP interior or exterior routing protocol?

Exterior (EGP)

TCP 3-way handshake steps

SYN, SYN-ACK, ACK

What is the even parity bit for the binary number 1010110?

0; there are 4 1s

What is the odd parity bit for the binary number 1001101?

1; there are 4 1s so add one to make total number odd.