IT 120 guide

Definition of a computer network

A combination of end and intermediary devices, physical or wireless connections, and rules (protocols) that allow separate devices to exchange information and share resources.

Primary role of end devices

To serve as the source or final destination of a network message by creating, requesting, receiving, or displaying information (e.g., PCs, laptops, smartphones, printers, servers).

Primary role of intermediary devices

To connect individual end devices or separate networks together, forwarding, directing, and controlling traffic flow across the network (e.g., switches, routers).

End device status of a network server

Communication originates from or terminates at the server itself, regardless of how many client hosts it serves simultaneously.

Primary function of a switch

To connect multiple wired devices within the same local area network (LAN) and forward traffic based on physical Layer 2 MAC addresses.

Primary function of a router

To connect different networks together and route traffic across networks based on logical Layer 3 IP addresses.

Primary function of a wireless access point (WAP)

To connect wireless devices to a local wired network using radio frequency signals.

Primary function of a modem

To convert signals between local network digital traffic and the access technology required by an Internet Service Provider (ISP).

Client/Server interaction model

An architecture where a client application sends a request for data or service, and a server stores, generates, or retrieves the resource to send back a response.

Definition and purpose of an SSID

Service Set Identifier; the unique human-readable name assigned to a Wi-Fi network that wireless clients select to join that specific network.

Distinction between an SSID and an IP address

An SSID is the name of a Wi-Fi network used for wireless association, whereas an IP address is a logical Layer 3 numerical identifier used to route packets to hosts.

Logical View vs. Physical View in Packet Tracer

Logical View displays device roles and network topology connections regardless of physical location; Physical View depicts the actual real-world location, room layout, and wiring closets of equipment.

Store-and-forward behavior in packet switching

A process where an intermediary device (like a router) must receive an entire packet before reading header information and forwarding it onto the outbound link.

Cause of packet loss in network buffers

Occurs when incoming data arrives at a router faster than it can be transmitted, filling the buffer queue and forcing excess incoming packets to be dropped.

Bottleneck effect on end-to-end throughput

The maximum data transfer speed across a network path is constrained by the link with the lowest bandwidth/capacity.

Primary role of Domain Name System (DNS)

To translate human-readable domain names (such as www.example.com) into numeric IP addresses required for network routing.

Difference between a URL and DNS

A URL specifies the complete location of a web resource, whereas DNS is the resolution protocol that maps the domain name within that URL to an IP address.

Four essential elements specified by communication protocols

1. Format (message structure)

2. Order (sequence of transmission)

3. Timing (speed and timeout rules)

4. Actions (responses to received messages)

The four layers of the TCP/IP protocol suite from top to bottom

1. Application Layer

2. Transport Layer

3. Internet Layer

4. Network Access Layer

The seven layers of the OSI model from top to bottom

Layer 7: Application Layer 6: Presentation Layer 5: Session Layer 4: Transport Layer 3: Network Layer 2: Data Link Layer 1: Physical

Mapping of OSI model layers to TCP/IP model layers

OSI Layers 7, 6, and 5 map to TCP/IP Application; OSI Layer 4 maps to TCP/IP Transport; OSI Layer 3 maps to TCP/IP Internet; OSI Layers 2 and 1 map to TCP/IP Network Access.

Data encapsulation process

The process where sender application data travels down protocol stack layers, with each layer prepending its own specific header control information.

Data decapsulation process

The process where receiving host layers inspect and strip headers from incoming data in reverse order as it moves up the stack to the application.

PDU names corresponding to each TCP/IP layer

Application Layer = Data Transport Layer = Segment Internet Layer = Packet Data Link Layer = Frame Physical Layer = Bits

Role of each layer during a web request transmission

Application (HTTP) specifies the requested resource; Transport (TCP) manages process ports; Internet (IP) identifies host IP addresses; Data Link (Ethernet) handles local interface MAC addresses; Physical converts bits to network signals.

Default TCP destination port for HTTP traffic

$$80$$

Default TCP destination port for HTTPS traffic

$$443$$

Comparison: Port number vs. IP address vs. MAC address

Port numbers (Transport Layer) identify specific software applications; IP addresses (Network Layer) identify host locations logically across networks; MAC addresses (Data Link Layer) identify physical hardware interfaces locally.

Subnet structure of a /24 network prefix ($255.255.255.0$)

The first three octets ($24$ bits) identify the shared network portion, and the final octet ($8$ bits) identifies individual host devices on that network.

Requirement for direct local communication without a router

Devices must reside within the same IP subnet (e.g., $192.168.10.10/24$ and $192.168.10.20/24$), allowing direct local switch frame delivery without Layer 3 routing.

Primary function of ARP (Address Resolution Protocol)

To discover and map the physical Layer 2 MAC address associated with a known local Layer 3 IPv4 address.

Cause of packet drop/delay on the first ping to a local IP address

The initial ping packet is delayed while the sending host broadcasts an ARP Request and waits for an ARP Reply to learn the destination MAC address.

Key differences: ARP vs. DNS

DNS maps human domain names to IP addresses across networks, whereas ARP maps local IP addresses to physical MAC addresses on the same local subnet.

Three-step operational process of a Layer 2 switch

1. Learn: Record source MAC address and ingress switchport.

2. Look: Search destination MAC address in the MAC address table.

3. Forward: Direct frame to the matching switchport or flood if unknown.

Realtime Mode vs. Simulation Mode in Packet Tracer

Realtime Mode executes network events in real time to test immediate connectivity, whereas Simulation Mode pauses traffic to step through individual PDU packets and protocol details.

Purpose of Cisco IOS and CLI

Cisco IOS is the operating system managing Cisco hardware, while the Command-Line Interface (CLI) provides precise text-based administration and configuration.

Console cable vs. Ethernet cable applications

A console cable connects a computer to a device's management port for configuration, while an ethernet cable connects devices to a network for data transfer.

Requirements for SSH remote device administration

An active network interface with an assigned IP address (such as an SVI on a switch), operational Layer 3 reachability, and configured SSH services.

Four primary Cisco IOS command modes and prompts

User EXEC: Switch> Privileged EXEC: Switch# Global Configuration: Switch(config)# Interface Configuration: Switch(config-if)#

Command sequence to enter Interface Configuration mode for FastEthernet 0/1

Switch> enable Switch# configure terminal Switch(config)# interface fastEthernet 0/1

Comparison: running-config vs. startup-config

running-config stores active temporary settings in volatile RAM; startup-config stores permanent saved configurations in non-volatile NVRAM.

IOS command to save active configuration changes permanently

copy running-config startup-config

Role of a Switch Virtual Interface (SVI / VLAN 1 IP)

Provides a logical IP address on a Layer 2 switch to enable remote IP management tasks such as SSH access and ping testing.

Correct encapsulation header order from sender data creation to media transmission

Application Data -> TCP Segment Header -> IP Packet Header -> Ethernet Frame Header/Trailer -> Physical Medium Bits

Recommended sequence for applying and verifying Cisco device changes

1. Apply configuration

2. Verify settings (show running-config)

3. Test connectivity (ping)

4. Save settings (copy running-config startup-config)