OSI Model: Session, Presentation, and Application Layers
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1
What does the OSI session layer do?
Establishes, manages, and terminates communication sessions.
2
Which OSI layer is the session layer?
Layer 5.
3
What is simplex communication?
Communication in one direction only.
4
What is half-duplex communication?
Communication in both directions, but only one direction at a time.
5
What is full-duplex communication?
Communication in both directions simultaneously.
6
Which OSI layer is the presentation layer?
Layer 6.
7
What does the OSI presentation layer do?
Formats, translates, encrypts, and compresses data.
8
What is data conversion at the presentation layer?
Translating data between formats or encodings.
9
What is encryption?
Transforming readable data into ciphertext using a cryptographic algorithm and key.
10
Which OSI layer is the application layer?
Layer 7.
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What does the OSI application layer provide?
Network services to user applications.
12
Which protocols operate at the application layer?
HTTP, FTP, SMTP, DNS, and Telnet.
13
What is a host-based application architecture?
A central host performs application functions while terminals provide user interaction.
14
What is a client/server architecture?
Clients request services or resources from servers.
15
What is cloud computing?
On-demand access to shared computing resources over a network.
16
What is an N-tier application architecture?
An application divided into multiple tiers with separate responsibilities.
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What is a peer-to-peer architecture?
An architecture in which devices can act as both clients and servers.
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What are the four main application processing functions?
Data storage, data access, processing logic, and user interface.
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What is the data storage function?
Maintaining application data for later use.
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What is the data access function?
Retrieving and modifying stored data.
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What is processing logic?
The rules and calculations that manipulate application data.
22
What is the user interface function?
Allowing users to interact with an application.
23
What is a network port?
A transport-layer number identifying an application or service on a host.
24
What is a network socket?
A communication endpoint identified by an IP address and port within a transport protocol.
25
Which protocol commonly uses TCP port 80?
HTTP.
26
Which port does FTP use for its control connection?
TCP port 21.
27
Which port does FTP traditionally use for active-mode data connections?
TCP port 20.
28
Which protocol commonly uses TCP port 23?
Telnet.
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Which protocol commonly uses TCP port 25?
SMTP.
30
What architecture does the World Wide Web primarily use?
Client/server.
31
What does a web browser send to request a resource?
An HTTP request.
32
What does a web server return after receiving an HTTP request?
An HTTP response.
33
What is malware?
Software designed to damage, disrupt, or gain unauthorized access to systems.
34
What is a denial-of-service attack?
An attack that makes a service unavailable to legitimate users.
35
Which OSI layer is the data link layer?
Layer 2.
36
What is the primary function of the data link layer?
Delivering frames across a local network link.
37
What data unit does the data link layer use?
A frame.
38
How does the data link layer build on the physical layer?
It organizes transmitted bits into frames and controls local link delivery.
39
What type of address is used at Layer 2?
A MAC address.
40
What is a MAC address?
A link-layer identifier assigned to a network interface.
41
What is the usual length of an Ethernet MAC address?
48 bits.
42
How does a switch learn MAC addresses?
It records incoming frames’ source MAC addresses and arrival ports.
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How does a switch forward a frame with a known destination MAC address?
It sends the frame through the associated destination port.
44
What does a switch do with an unknown unicast destination?
Floods the frame through other eligible ports in the same VLAN.
45
What is bridging?
Connecting LAN segments and forwarding frames using MAC addresses.
46
What does CSMA/CD stand for?
Carrier Sense Multiple Access with Collision Detection.
47
What does carrier sensing in CSMA/CD mean?
Checking whether the shared medium is idle before transmitting.
48
What happens after a collision in CSMA/CD?
Devices stop transmitting, wait a randomized backoff interval, and retry.
49
Where is CSMA/CD used?
Shared, half-duplex Ethernet.
50
Does full-duplex switched Ethernet use CSMA/CD?
No.
51
What does STP stand for?
Spanning Tree Protocol.
52
What problem does STP prevent?
Layer 2 switching loops.
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How does STP prevent loops?
It blocks redundant paths to create a loop-free topology.
54
What is the STP root bridge?
The reference switch used to calculate the spanning tree.
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How does STP choose the root bridge?
The switch with the lowest bridge ID becomes the root.
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How does STP support resiliency?
It can activate an alternate path after a topology failure.
57
What is link aggregation?
Combining multiple physical links into one logical link.
58
What does LACP stand for?
Link Aggregation Control Protocol.
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What does LACP do?
Negotiates and maintains a group of aggregated links.
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What are two benefits of link aggregation?
Increased aggregate bandwidth and link redundancy.
61
What is a hierarchical backbone?
A backbone organized into multiple network tiers.
62
What is a flat backbone?
A backbone with little or no hierarchical layering.
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What is a collapsed backbone?
A backbone concentrated in a central device or small group of devices.
64
Which OSI layer is the network layer?
Layer 3.
65
What is the primary function of the network layer?
Routing packets between networks using logical addresses.
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What data unit does the network layer use?
A packet.
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What type of address does IP routing use?
An IP address.
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What is a routed protocol?
A protocol whose packets can be forwarded between networks.
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What is an example of a routed protocol?
IP.
70
What is a routing protocol?
A protocol routers use to exchange reachability and route information.
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What is a routing table?
A list of destination networks and the routes used to reach them.
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What is a next hop?
The next router to which a packet is forwarded.
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What is static routing?
Routing using manually configured routes.
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What is dynamic routing?
Routing that uses protocols to learn and update routes automatically.
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What is path determination?
Selecting a route to a destination network.
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What is a routing metric?
A value used to compare routes.
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What are examples of routing metrics?
Hop count, bandwidth, delay, and cost.
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What is routing convergence?
The state in which routers have consistent routing information after changes.
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What is routing load balancing?
Distributing traffic across multiple available paths.
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What is distance-vector routing?
Routing that exchanges destination distances and next-hop information with neighbors.
81
What is link-state routing?
Routing that distributes link information so routers can calculate paths from a topology map.
82
What is an interior gateway protocol?
A routing protocol used within one autonomous system.
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What is an exterior gateway protocol?
A routing protocol used between autonomous systems.
84
What is an autonomous system?
A group of networks managed under a common routing policy.
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What does RIP stand for?
Routing Information Protocol.
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What type of routing protocol is RIP?
A distance-vector interior gateway protocol.
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What metric does RIP use?
Hop count.
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What is the maximum reachable hop count in RIP?
15 hops.
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What does a RIP metric of 16 mean?
The destination is unreachable.
90
What is split horizon?
A rule preventing a route from being advertised back through the interface where it was learned.
91
What problem does split horizon help reduce?
Routing loops.
92
What does OSPF stand for?
Open Shortest Path First.
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What type of routing protocol is OSPF?
A link-state interior gateway protocol.
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What algorithm does OSPF use to calculate shortest paths?
Dijkstra’s shortest-path-first algorithm.
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What metric does OSPF use?
Cost, typically derived from interface bandwidth.
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What does IGRP stand for?
Interior Gateway Routing Protocol.
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What type of routing protocol is IGRP?
A Cisco-developed distance-vector interior gateway protocol.
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What does EIGRP stand for?
Enhanced Interior Gateway Routing Protocol.
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What type of routing protocol is EIGRP?
An advanced distance-vector interior gateway protocol.
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What algorithm does EIGRP use?
Diffusing Update Algorithm, or DUAL.
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Which factors does EIGRP use by default in its metric?
Bandwidth and delay.
102
What does BGP stand for?
Border Gateway Protocol.
103
What type of routing protocol is BGP?
A path-vector routing protocol.
104
What is BGP’s main role?
Exchanging routing information between autonomous systems.
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What BGP attribute lists the autonomous systems a route traverses?
AS_PATH.
106
What is first-hop redundancy?
Providing an alternate router if a host’s default gateway fails.
107
What does VRRP stand for?
Virtual Router Redundancy Protocol.
108
What does VRRP provide?
A shared virtual default gateway with router failover.
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What does HSRP stand for?
Hot Standby Router Protocol.
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What does HSRP provide?
A Cisco gateway redundancy mechanism using active and standby routers.
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What does GLBP stand for?
Gateway Load Balancing Protocol.
112
What does GLBP provide?
Default-gateway redundancy and load balancing across multiple routers.
113
What is the core or backbone of a network?
The high-speed infrastructure connecting major network segments.
114
What is a WAN?
A wide area network connecting networks across large geographic areas.
115
What is a data center?
A facility housing computing, storage, and networking equipment.
116
What is the distribution layer of a network?
The layer that aggregates access connections and applies network policies.
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What is the access edge of a network?
The portion where end-user devices connect.
118
What is a DMZ?
A separate network segment for externally accessible services.
119
What does IPAM stand for?
IP Address Management.
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What does IPAM manage?
IP address allocation, tracking, and related address-space information.
121
What does DHCP stand for?
Dynamic Host Configuration Protocol.
122
What does DHCP provide?
Automatic IP addressing and other network configuration settings.
123
What does DNS stand for?
Domain Name System.
124
What does DNS do?
Resolves domain names into IP addresses and other records.
125
What does NTP stand for?
Network Time Protocol.
126
What does NTP do?
Synchronizes device clocks over a network.
127
What does a network hub do?
Repeats incoming signals to its other ports.
128
At which OSI layer does a hub operate?
Layer 1.
129
What does a Layer 2 switch do?
Forwards frames using MAC addresses.
130
What does a router do?
Forwards packets between IP networks.
131
What does a firewall do?
Permits or blocks network traffic according to security rules.
132
What does IDS stand for?
Intrusion Detection System.
133
What does an IDS do?
Monitors activity and alerts on suspected intrusions.
134
What does IPS stand for?
Intrusion Prevention System.
135
What does an IPS do?
Detects and actively blocks suspected malicious traffic.
136
What does WAP stand for in networking?
Wireless Access Point.
137
What does a wireless access point do?
Connects wireless clients to a network.
138
What does a wireless range extender do?
Retransmits wireless signals to extend coverage.
139
What is an IoT device?
A network-connected physical device that senses, processes, or exchanges data.
140
What does VoIP stand for?
Voice over Internet Protocol.
141
What does a VoIP device do?
Sends and receives voice communications over IP networks.
142
What is identification in access control?
Claiming an identity, such as by entering a username.
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What is authentication?
Verifying a claimed identity.
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What is authorization?
Determining which resources or actions an authenticated identity may access.
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What is accounting in network access control?
Recording user activity and resource usage.
146
What does AAA stand for?
Authentication, Authorization, and Accounting.
147
How do wireless networks support mobility?
Users can connect while moving within wireless coverage.
148
How can wireless networks reduce installation costs?
They reduce the need for cabling to individual devices.
149
How do wireless networks support scalability?
They allow additional clients to connect without individual cable runs.
150
What does the IEEE 802.11 family define?
Wireless LAN standards.
151
Which frequency band does 802.11b use?
2.4 GHz.
152
Which frequency band does 802.11a use?
5 GHz.
153
Which frequency band does 802.11g use?
2.4 GHz.
154
Which frequency bands does 802.11n support?
2.4 GHz and 5 GHz.
155
Which frequency band does 802.11ac use?
5 GHz.
156
Which Wi-Fi generation corresponds to 802.11n?
Wi-Fi 4.
157
Which Wi-Fi generation corresponds to 802.11ac?
Wi-Fi 5.
158
Which Wi-Fi generation corresponds to 802.11ax?
Wi-Fi 6.
159
What does WLAN stand for?
Wireless Local Area Network.
160
What does OSA stand for in WLAN security?
Open System Authentication.
161
Does Open System Authentication verify possession of a shared secret?
No.
162
What does SKA stand for in WLAN security?
Shared Key Authentication.
163
How does Shared Key Authentication verify a client?
It uses a challenge-response process based on a shared WEP key.
164
What does EAP stand for?
Extensible Authentication Protocol.
165
What does EAP provide?
A framework supporting multiple authentication methods.
166
What does WEP stand for?
Wired Equivalent Privacy.
167
What is a major weakness of WEP?
Its cryptographic design allows attackers to recover keys.
168
What does WPA stand for?
Wi-Fi Protected Access.
169
What protocol did original WPA introduce to improve on WEP?
TKIP.
170
What does AES stand for?
Advanced Encryption Standard.
171
What type of encryption algorithm is AES?
A symmetric block cipher.
172
What is a client-to-client WLAN attack?
An attack by one wireless client against another.
173
What is a WLAN denial-of-service attack?
An attack that disrupts wireless network availability.
174
What is a WLAN insertion attack?
Introducing an unauthorized wireless device or access point into a network.
175
What is a WLAN interception attack?
Capturing wireless communications without authorization.
176
What is IEEE 802.1X?
A framework for port-based network access control.
177
What are the three main roles in 802.1X?
Supplicant, authenticator, and authentication server.
178
What is the supplicant in 802.1X?
The client requesting network access.
179
What is the authenticator in 802.1X?
The switch or access point controlling network access.
180
What is the authentication server in 802.1X?
The server that validates client credentials.
181
What does RADIUS stand for?
Remote Authentication Dial-In User Service.
182
What role does RADIUS commonly serve in 802.1X?
It carries authentication information between the authenticator and authentication server.
183
What is symmetric encryption?
Encryption using the same shared secret key for encryption and decryption.
184
What is asymmetric encryption?
Encryption using a mathematically related public and private key pair.
185
Which key creates a digital signature?
The signer’s private key.
186
Which key verifies a digital signature?
The signer’s public key.
187
What does a digital signature help verify?
The origin and integrity of signed data.
188
Does a digital signature alone conceal a message’s contents?
No.
189
What did IEEE 802.11i establish?
Enhanced wireless authentication and encryption mechanisms.
190
Which Wi-Fi security certification implements 802.11i?
WPA2.
191
What does TKIP stand for?
Temporal Key Integrity Protocol.
192
What does TKIP improve compared with WEP?
Per-packet key mixing and message integrity.
193
What does CCMP stand for?
Counter Mode with Cipher Block Chaining Message Authentication Code Protocol.
194
Which cipher does CCMP use?
AES.
195
What does CCMP provide?
Data confidentiality, integrity, and replay protection.
196
What is MAC address filtering?
Allowing or denying devices based on their MAC addresses.
197
Why is MAC address filtering weak as a sole security measure?
Attackers can spoof an allowed MAC address.
198
What is RF design in WLAN planning?
Planning radio frequencies, channels, power levels, and access point placement.
199
What does WLAN coverage describe?
The area where wireless signal quality supports usable connections.
200
What does WLAN capacity describe?
The number of clients and amount of traffic a WLAN can support.
201
What is WLAN site qualification?
Assessing whether a location can meet wireless coverage, capacity, and installation requirements.
202
What can a wireless site survey identify?
Coverage gaps, interference, and suitable access point locations.
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