CH.2 Models and Network devices

[2.1] Why use a networking reference model?

It organizes network functions into layers to support understanding / design / and troubleshooting.

[2.2] List the seven OSI layers from 1 to 7.

Physical / Data Link / Network / Transport / Session / Presentation / Application.

[2.2] What does OSI Layer 1 do?

Transmits bits as physical signals over media. includes cabling / connectors / and signaling.

[2.2] What does OSI Layer 2 do?

Handles local-link frames / MAC addressing / and Ethernet switching.

[2.2] What does OSI Layer 3 do?

Handles logical addressing and packet routing between networks.

[2.2] What does OSI Layer 4 do?

Provides transport between applications using protocols such as TCP and UDP and their port numbers.

[2.2] What does OSI Layer 5 do?

Establishes / manages / and ends communication sessions.

[2.2] What does OSI Layer 6 do?

Handles data representation / including encoding / compression / and encryption in the conceptual model.

[2.2] What does OSI Layer 7 do?

Provides network services used by applications / such as HTTP and DNS.

[2.2] Which OSI layer is associated with MAC addresses?

Layer 2 / Data Link.

[2.2] Which OSI layer is associated with IP addresses?

Layer 3 / Network.

[2.2] Which OSI layer is associated with TCP/UDP ports?

Layer 4 / Transport.

[2.2] What is encapsulation?

Adding protocol information as data moves down the sender's network stack.

[2.2] What is decapsulation?

Processing and removing protocol information as data moves up the receiver's network stack.

[2.2] What is the usual encapsulation sequence?

Application data / TCP segment or UDP datagram / IP packet / link-layer frame / transmitted bits.

[2.2] What is the Layer 2 protocol data unit called?

A frame.

[2.2] What is the Layer 3 protocol data unit called?

A packet.

[2.2] What are the TCP and UDP Layer 4 data units called?

A TCP segment and a UDP datagram.

[2.2] A cable is disconnected. Which OSI layer should you investigate first?

Layer 1 / Physical.

[2.2] A host has the wrong IP subnet mask. Which OSI layer is most directly involved?

Layer 3 / Network.

[2.2] An ACL blocks TCP port 443. Which layer identifies that port?

Layer 4 / Transport.

[2.3] List the four TCP/IP model layers from bottom to top.

Network Access / Internet / Transport / Application.

[2.3] Which OSI layers map to TCP/IP Network Access?

Layers 1 and 2.

[2.3] Which OSI layer maps to TCP/IP Internet?

Layer 3.

[2.3] Which OSI layer maps to TCP/IP Transport?

Layer 4.

[2.3] Which OSI layers map to TCP/IP Application?

Layers 5 / 6 / and 7.

[2.4] What does a hub do?

Repeats incoming signals to its other ports without MAC-based forwarding decisions.

[2.4] What does a repeater do?

Regenerates a signal to extend its transmission reach.

[2.4] What does a media converter do?

Connects compatible links using different media / such as copper Ethernet and fiber Ethernet.

[2.4] What does a modem do?

Modulates and demodulates signals for communication over a supported carrier medium.

[2.4] What does an Ethernet switch use to forward frames?

A MAC address table associating learned MAC addresses with ports.

[2.4] How does a switch learn MAC addresses?

It records the source MAC address of an incoming frame and the port where it arrived.

[2.4] What does a router use to choose packet forwarding paths?

Its routing table and the packet's destination IP address.

[2.4] How does a Layer 3 switch differ from a basic Layer 2 switch?

It can also route between IP networks when configured to do so.

[2.4] What does a wireless access point do?

Provides wireless clients with connectivity to a network / typically bridging them to a wired LAN.

[2.4] What does a wireless LAN controller do?

Centrally manages supported access points and wireless configuration.

[2.4] What does a firewall do?

Permits or blocks traffic based on configured security rules.

[2.4] What is the main difference between IDS and IPS?

An IDS detects and alerts. an IPS can actively block suspicious traffic.

[2.4] What does a load balancer do?

Distributes requests or connections across backend resources.

[2.4] What does a proxy do?

Acts as an intermediary for requests between clients and other services.

[2.4] Must every networking device operate at only one OSI layer?

No. Multifunction devices can inspect or perform functions at several layers.

[2.5] What does BYOD mean?

Bring Your Own Device: personally owned devices used to access organizational resources.

[2.5] What is IoT?

Internet of Things: connected devices such as sensors / cameras / and smart appliances.

[2.5] What is IIoT?

Industrial Internet of Things: connected sensors and equipment used in industrial environments.

[2.5] What is an ICS?

An industrial control system that monitors or controls industrial processes.

[2.5] Why separate guest / IoT / and industrial devices from business systems?

To limit access and reduce the impact of compromised or less-trusted devices.

[2.6-2.7] What should you identify in a packet capture?

Source/destination MAC and IP addresses / protocol layers / transport ports when present / and relevant flags or errors