Top 50 CCNA Interview Questions and Answers 2024 

  • By Gandhar Bodas
  • March 4, 2024
  • CCNA
Top 50 CCNA Interview Questions and Answers 2024 

Top 50 CCNA Interview Questions and Answers 2024 

Prepare for success in CCNA interviews with our comprehensive guide featuring the top 50 CCNA interview questions and answers 2024.

Q1) What is Network? 

🡺 A computer network can be described as a system of interconnected devices that  can communicate using some common standards called the Internet protocol  suite or TCP/IP. These devices communicate to exchange network resources, such  as files and printers, and network services. 

Example: The example above shows that the two computers are directly  connected using a cable. This small network can exchange data between just  these two computers. 

Q2) What is Point to Point Connection? 


A point-to-point connection is a direct connection between two nodes. Data  transmitted by one node goes directly to the other. 

Dial-up modem connections are point-to-point connections

Q3) What is the Gateway-to-Gateway protocol? 


The Gateway-to-Gateway Protocol (GGP) is an obsolete routing protocol used in  early versions of the Internet.  

It was used to exchange routing information between gateway hosts in different  networks to facilitate routing decisions. GGP was designed to work with the older  version of the Internet Protocol (IP) known as IPv4.  

However, GGP has been largely replaced by more efficient and scalable routing  protocols such as Border Gateway Protocol (BGP) and Open Shortest Path First  (OSPF) in modern networking environments. 

Q4) What is Protocol? 


A protocol is a set of rules and conventions that govern how data is exchanged between devices or systems.  

In networking, protocols define the format and sequence of messages exchanged  between devices, as well as the actions taken by devices in response to those  messages.  

Protocols ensure that devices can communicate effectively and understand each  other’s messages.  

Examples of networking protocols include the Internet Protocol (IP) for routing  data across the Internet, the Transmission Control Protocol (TCP) for reliable data  transmission, and the Hypertext Transfer Protocol (HTTP) for transmitting web  pages over the Internet.

Q5) Explain difference between Router, Switch and Hub? 🡺

Hub  Switch  Router
Hub is a physical layer  device i.e. layer 1.  Switch is a data link layer  device i.e. layer 2.  Router is a network layer  device i.e. layer 3. 
A Hub works on the basis  of broadcasting. Switch works on the basis  of MAC address. A router works on the  basis of IP address.
A Hub is a multiport  

repeater in which a  

signal introduced at the  input of any port appears  at the output of the all  available ports.

A Switch is a tele 

communication device  which receives a message  from any device connected  to it and then transmits  the message only to the  device for which the  

message is intended.

A router reads the header  of incoming packet and  forward it to the port for  which it is intended there  by determines the route.  It can also perform  

filtering and  


Hub is not an intelligent  device that may include  amplifier on repeater. A Switch is an intelligent  device as it passes on the  message to the selective  device by inspecting the  address. A route is more  

sophisticated and  

intelligent device as it  can read IP address and  direct the packets to  

another network with  specified IP address.  Moreover routers can  

built address tables that  helps in routing  


At least single network is  required to connect. At least single network is  required to connect. Router needs at least two  networks to connect.
Hub is cheaper as  

compared to switch and  router.

Switch is an expensive  device than hub. Router is a relatively  much more expensive  device than hub and  switch.
Speed of original hub  10Mbps and modern  internet hub is 100Mbps. Maximum speed is  

10Mbps to 100Mbps.

Maximum speed for  

wireless is 1-10 Mbps  and maximum speed for  wired connections is 100  Mbps.

Hubs are used in LANs.  Switch is used in LANs.  Routers are used in  

LANs, MANs and WANs.


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Q6) What are the criteria necessary for an effective and efficient  network? 


The most important criteria are performance, reliability, and security. A) Performance:  

– It measures how well a network can support communication between two  nodes in the Network or with nodes of other networks in the global scope. 

– The two major tasks in a network are the Transmission and Reception of  information. 

– We need to focus on how fast a message is transmitted and how fast a node can  receive a request and find the needed information. 

– Hence, to measure the performance of a network, here are the major factors to  be considered: 

  1. a) Transit Time: The total time a node takes to transmit a message from the beginning until the last character of the message. Transit stands for  
  2. b) Response Time: The total time a nodes takes to process an inquiry or a request from another node / device and respond. It is the time between the inquiry’s end and the response’s beginning. 
  3. c) Throughput: Throughput measures how much data is transferred successfully from the sender node to the receiver node in a particular time It is measured in bits per second or data per second. 
  4. d) Bandwidth: The max possible throughput capacity of the Network. We can measure it in bits, megabits, or gigabits per second. It defines the highest limit.
  5. e) Delay / Latency: As, we discussed, Throughput is the number of data packets successfully delivered in a given time. Delay is the measure of time taken to do the delivery. 
  6. B) Reliability:

– It is the degree to which a network is trustworthy, consistent, and dependable. 

– The Reliability of a network is measured by the frequency of failures it is  undergoing and the time it takes to recover from the failures. 

– Overall, the Robustness of the Network at times of catastrophic events is  measured to check how reliable the Network is.


Robustness of the Network = The ability to maintain the function and  property of the network that the damaged network has it network  robustness. 

  1. C) Security:

– It measures how the Network secures the data amid failures and attacks and the  policies and procedures it implements to protect itself from damages and un authorized access.  

– In Reliability, the frequency of failures is checked. 

– In Security, network attacks and data breaches are checked. 

Q7) What is the Ipconfig command, and why is it used? 🡺 

The IPCONFIG command shows the IP address information for a computer. From  the output, we can find the IP address, DNS IP address, and gateway IP address  given to the computer. 

Q8) Let’s say a virtual machine is suddenly turned off. Which VM  log files should be looked at to troubleshoot what’s wrong? 


If something like this happens, an administrator needs to analyze the issue by  looking at the log files named vmware.log and hostd.log.  

The hostd.log log files explain the agent that maintains and configures the ESXi  host and virtual machines.  

The Vmare.log log files keep track of the activity on the ESX host and the virtual  machines it hosts. 

Q9) What common problems with software can cause network  problems? 


Several of the following can contribute to network-related problems: 

Error in configuration 

Application conflicts 

Client-server problems 

Security issues 

Protocol mismatch

User policy and rights issues 

Q10) What would you do to troubleshoot what was wrong with an  FTP server? 

🡺 If you’re having issues with your FTP server, here are the three things you  should try: 

Ping is a simple tool for checking network connectivity. The “echo request”  is a part of ICMP that is used by the “ping” command (Internet Control  Message Protocol). To check if a device is online or active, you can use the  “ping” command, equivalent to sending an echo request. 

Check the available ports with Nmap (20 and 21). You may evaluate your  firewall and other security measures with the help of the Nmap-hosted  security tool. Ports in modern operating systems are numeric addresses  used for networking. As a general rule, various services make use of  separate ports. It is essential to know which ports are open and closed to  prevent any security breaches resulting from the improper port  configuration. 

Find out if a firewall is preventing traffic from reaching the server. 

Q11) What is the difference between OSI and TCP/IP Model? 🡺

The full form of TCP/IP is Transmission Control  Protocol/ Internet Protocol. The full form of OSI is Open Systems  Interconnection.
It is a communication protocol that is based on  standard protocols and allows the connection of  hosts over a network. It is a structured model which deals which the  functioning of a network.
In 1982, the TCP/IP model became the standard  language of ARPANET. In 1984, the OSI model was introduced by the  International Organisation of Standardization  (ISO).
It comprises of four layers: 

Network Interface 




It comprises seven layers: 


Data Link 







It follows a horizontal approach.  It follows a vertical approach.
The TCP/IP is the implementation of the OSI  Model. An OSI Model is a reference model, based on  which a network is created.
It is protocol dependent.  It is protocol independent.


Q12) What is meant by and localhost? 

🡺The localhost or loopback address is These systems are often only  accessible to the largest clients or the Internet’s founding members. Pinging the  server to see if it responds is the first step in diagnosing connection problems. 

There could be many reasons why the server isn’t responding, such as a  malfunctioning network, faulty wiring, or a malfunctioning network card. Pinging indicates that the hardware is functioning properly because it is a  loopback connection on the NIC. 

With most network operations, and localhost refer to the same thing. 

Q13) What are different ways to send data through networks? 🡺 

In computer networks, there are three different ways that data can be sent. Here  is a list of them, 

Simplex: Simplex is one-way data transport. Simplex mode transfers data  from sender to receiver or receiver to sender—radio signal, computer-to printer signal, Etc. 

Half Duplex: Both directions can transfer data, but not simultaneously.  Data is sent and received. In internet browsing, a user submits a request to  the server, which then sends back the web page. 

Full Duplex: Simultaneous bidirectional data transfer. Two-way highways,  phone calls, Etc.


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Q14) What’s the difference between FTP and TFTP application layer protocols? 


The simple file transfer protocol (TFTP) describes a local host retrieving  data from a remote host.  

It takes advantage of the standard packet delivery features of UDP.  However, it is unreliable and lacks security. 

TCP/IP often provides the File Transfer Protocol to transfer data between  hosts (FTP). Because it takes advantage of TCP’s facilities, it is dependable  and safe.  

Two connections are established between the hosts: one for command and  control information and another for actual data transfer. 

Q15) When were OSI model developed and why it’s standard called 802.XX and so on? 


The OSI (Open Systems Interconnection) model was developed by the  International Organization for Standardization (ISO).  

It was first introduced in 1984 as a conceptual framework to standardize  and organize the functions of a telecommunication or computing system  into seven distinct layers.  

The goal was to facilitate communication and interoperability between  different systems and technologies. 

The term “802.XX” refers to a series of IEEE (Institute of Electrical and  Electronics Engineers) standards related to networking.  

The numbers following “802” correspond to specific working groups within  the IEEE that focus on various aspects of networking.  

The IEEE 802 standards cover a wide range of protocols and technologies,  including Ethernet (802.3), Wi-Fi (802.11), and many others. 

The naming convention “802” is simply a reference to the project number  assigned to the working group within the IEEE that develops and maintains  these standards.  

It doesn’t directly correlate with the OSI model; instead, it’s a separate set  of standards that address various aspects of network communication and  connectivity.

Q16)What is the difference between tracert and traceroute? 🡺 

tracert and traceroute are commands used to trace the route that packets take to  reach a destination on a network.  

The main difference between them lies in the operating systems and platforms  where they are commonly used: 

1) Tracert: 

Platform: Tracert is a command-line utility used in Windows operating  systems. 

Syntax: In Windows, you use the tracert command followed by the  destination IP address or domain name. 

Example: tracert 

2) Traceroute: 

Platform: Traceroute is the equivalent command used in Unix-like  operating systems, including Linux and macOS. 

Syntax: In Unix-like systems, you use the traceroute command followed by  the destination IP address or domain name. 

Example: traceroute 

Q17) IEEE standard for wireless networking? 


The IEEE standard for wireless networking is defined under the IEEE 802 family of  standards. Several standards within this family address various aspects of wireless  networking, including different types of wireless technologies. Some of the  prominent IEEE 802 standards for wireless networking include: 

1) IEEE 802.11: This standard defines the specifications for Wireless Local  Area Networking (WLAN) commonly known as Wi-Fi. It includes various  amendments and updates, such as 802.11a, 802.11b, 802.11g, 802.11n,  802.11ac, and 802.11ax (Wi-Fi 6).

2) IEEE 802.15: This family of standards focuses on Wireless Personal Area  Networks (WPANs). One notable standard is IEEE 802.15.1, which is the  basis for Bluetooth technology. 

3) IEEE 802.16: This standard is known as WiMAX (Worldwide Interoperability  for Microwave Access) and is designed for broadband wireless access over  longer distances. It includes specifications for both fixed and mobile  broadband wireless systems. 

4) IEEE 802.22: This standard is designed for Wireless Regional Area Networks  (WRANs) and utilizes cognitive radio technology to operate in unused TV  spectrum. 

Q18) What is 100BaseFX? 


100BaseFX refers to one of the Ethernet standards defined by the IEEE 802.3u  committee for Fast Ethernet over optical fiber.  

The “100” in 100BaseFX denotes a data rate of 100 megabits per second (Mbps),  and “FX” indicates that it uses a fiber optic medium.  

Fast Ethernet represents an improvement over traditional Ethernet, which  operates at 10 Mbps. 

Key features of 100BaseFX: 

Data Rate: It supports a data rate of 100 Mbps, providing a tenfold increase  in speed compared to traditional Ethernet. 

Medium: 100BaseFX operates over optical fiber, which offers advantages  such as greater bandwidth, immunity to electromagnetic interference, and  the ability to transmit data over longer distances compared to copper  cabling. 

Topology: It can be used in various network topologies, including point-to point links and multi-mode or single-mode fiber optic cables. 

Standards: 100BaseFX is part of the IEEE 802.3u standard, which defines  Fast Ethernet. Specifically, the standard for 100BaseFX is IEEE 802.3u-1995. Connectors: It typically uses fiber optic connectors such as SC (Subscriber  Connector) or ST (Straight Tip). 

100BaseFX provides a cost-effective solution for upgrading network speeds in  environments where the installation of new copper cabling may be impractical or  where the advantages of fiber optics are desired.  

It played a significant role in the transition from traditional Ethernet to Fast  Ethernet in the evolution of networking technologies.

Q19) Which layer provides logical addressing that routers will use  for path determination? 


The Layer 3, or Network Layer, is responsible for finding the right path for the  data packet to reach its destination based on Logical Addresses (means addresses  not really present on the network node). 

Q20) Which layer specifies voltage, wire speed, and pinout cables  and moves bits between devices? 

🡺 Physical Layer 

Q21) Which layer combines bits into bytes and bytes into frames,  uses MAC addressing, and provide error detection? 

🡺 The Data Link Layer combines bits into bytes and bytes into frames and uses  MAC addressing. The Data Link Layer is the second layer of the OSI model and is  responsible for providing reliable and error-free communication over a physical  link. 

Q22) Which layer is responsible for keeping the data from  different applications separate on the network? 

🡺 Session Layer 

Q23) Which layer provides the physical transmission sof the data  and handless error notification, network topology, and flow  control? 

🡺 The Data Link layer (also called Layer 2) provides the physical transmission of  the data and handles error notification, network topology, and flow control. 

Q24) Which layer is responsible for converting data packets from  the Data Link layer into electrical signals? 


The Physical layer takes frames from the Data Link layer and encodes the 1s and  0s into a digital signal for transmission on the network medium.

Q25) Utilizing RIP, what is the limit when it comes to number of  hops? 


In RIP version 1, the maximum allowable hop count is 15. This means that a  route will be considered unreachable if the number of hops exceeds 15. A  hop count represents the number of routers a packet must traverse to  reach its destination. 

In RIP version 2, the maximum hop count is also 15 by default. However,  RIP version 2 introduces support for a feature called “infinite” or  “unreachable” metric. Instead of relying solely on the hop count, RIP  version 2 allows routes to be marked as unreachable by setting their metric  to a special value, effectively indicating that the route is unreachable. This  provides a more flexible mechanism for expressing unreachable routes. 

Q26) How do you stop RIP updates from propagating out an  interface on a router? 


In RIP (Routing Information Protocol), you can control the propagation of updates  out of a specific interface using the “passive-interface” command.  

This command prevents RIP updates from being sent or received on a particular  interface without affecting the overall operation of RIP on other interfaces. 

Here’s how you can use the “passive-interface” command: 

Command: Router(config)# router rip 

Command: Router(config-router)# passive-interface [interface_type  interface_number] 

Router rip: Enters the RIP configuration mode. 

passive-interface [interface_type interface_number]: Marks the specified  interface as passive, preventing RIP updates from being sent or received on that  interface. 


Router(config)# router rip 

Router(config-router)# passive-interface GigabitEthernet0/0 

Note: In this example, RIP updates will not be sent or received on the  GigabitEthernet0/0 interface. 

You would replace “GigabitEthernet0/0” with the actual interface you want to  make passive. 

Q27) Does EIGRP require an ip default-network command to propagate a  default route? 


No, EIGRP does not require the “ip default-network” command to propagate a  default route. EIGRP can propagate a default route using either a static route or  by redistributing a static route into EIGRP. 

To propagate a default route in EIGRP, you can use the following methods: 

Redistribution: If the default route is present in the routing table as a static route,  you can redistribute it into EIGRP using the redistribute static command under the  EIGRP process. 

Command: router eigrp <AS-number> 

redistribute static 

Summary Routes: You can advertise a summary route that covers all possible  default routes. This is done using the ip summary-address command under the  EIGRP interface configuration. 

Command: interface <interface> 

ip summary-address eigrp <AS-number> 

The ip default-network command is used with other routing protocols like RIP  and IGRP to advertise a default route. In EIGRP, you typically use the methods  mentioned above to propagate a default route. 

Q28) Does EIGRP require an ip default-network command to propagate a  default route? 


Yes, this command makes it easy to determine why an EIGRP neighbour was reset Q29) What is Advertised distance? 


In EIGRP (Enhanced Interior Gateway Routing Protocol), the Advertised Distance  (AD) is the total metric of a route as advertised by a neighboring router. It  represents the cost to reach a destination network as advertised by the  neighbor.

When a router receives an EIGRP update from a neighbor, it includes the AD in  the update packet. The receiving router uses this information to calculate its  feasible distance (FD) to the destination network, which is the sum of the AD and  the cost to reach the neighbor advertising the route. 

The AD is used in the DUAL (Diffusing Update Algorithm) to determine the best  path to a destination network. Each router maintains a topology table containing  information about all known routes, including the AD and the FD. By comparing  the FD of its neighbors with its own FD to the same destination, a router can  determine if the neighbor’s path is a better route to reach the destination  network. 

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Q30) What is successor? 


In EIGRP (Enhanced Interior Gateway Routing Protocol), a successor is the best  path to reach a destination network. It is the route with the lowest feasible  distance (FD) among all known routes to that destination. 

When a router receives EIGRP updates from its neighbours, it calculates the FD for  each route based on the advertised distance (AD) received from the neighbour  and the cost to reach that neighbour. The route with the lowest FD is chosen as  the successor route. 

The successor route is used to forward traffic to the destination network. EIGRP  also maintains backup routes, known as feasible successors, which are routes that  have a higher FD than the successor but are still considered loop-free backup  paths. If the successor route fails, one of the feasible successors can be used as  the new successor without causing a routing loop. 

Q31) If there are two EIGRP processes that run and two equal paths are learned, one by each EIGRP process, do both routes get installed? 🡺 

Yes, if there are two EIGRP processes running on a router and each process learns  an equal-cost path to a destination network, both routes will be installed in the  routing table.  

Each EIGRP process maintains its own topology table and calculates its own best  paths independently.  

If both processes determine that a path is the best path to a destination, both  routes will be installed in the routing table and the router will load-balance traffic  between them.

Q32) What is the difference in metric calculation between EIGRP and IGRP? 


Characteristics  IGRP  EIGRP
Convergence time  Slow  Fast
Administrative distance  100  Internal: 90; External:  170
Maximum hop count  100  224
Route summarization  Classful  Classless
Support for VLSM and  CIDR No  Yes
Supports multiple  

network layer protocols

No  Yes
Triggered updates  No  Yes
Neighbour discovery and  maintenance Broadcast-based  Multicast-based
Scalability  Limited  High
Compatibility with Cisco  devices Yes  Yes
Full Form  Interior Gateway Routing  Technology (IGRP) Enhanced Interior  

Gateway Routing  

Protocol (EIGRP)


Q33) Which command in OSPF shows the network LSA information? 🡺 

In OSPF (Open Shortest Path First), the command to display network LSA (Link  State Advertisement) information is show ip ospf database network.  

This command displays information about network LSAs in the OSPF database,  including the router ID of the advertising router, the network mask, and the list of  routers connected to the network. 

Q34) What is the main importance of STUB network? Why it is been developed in OSPF? 


A stub network in OSPF (Open Shortest Path First) is a network that has only one  exit point, typically towards a single router or a single point of connection to the 

OSPF domain. The main importance of stub networks in OSPF is to reduce the size  of the OSPF routing table and to simplify routing in certain network topologies. 

Here are some key reasons why stub networks were developed in OSPF: 

  1. a) Reduced Routing Table Size: By designating a network as a stub network, OSPF routers in the network do not need to store detailed routing information for external networks beyond the stub area. Instead, they only  need to know the route to the exit point of the stub network, reducing the  size of the routing table. 
  2. b) Reduced OSPF Traffic: OSPF routers in a stub network do not participate in OSPF routing updates beyond the stub area. This reduces OSPF control traffic and processing overhead on routers within the stub network. 
  3. c) Simplified Configuration: Configuring a network as a stub network simplifies OSPF configuration, as routers in the stub network only need to be configured with basic OSPF settings and do not require complex routing  policies or filtering. 
  4. d) Increased Stability: By limiting the scope of OSPF routing updates within the stub network, changes in external networks are less likely to affect the stability of the stub network. 

Overall, stub networks in OSPF are a mechanism to optimize routing in certain  network scenarios, providing a balance between routing efficiency and network  complexity. 

Q35) If router ID are same between OSPF enabled routers will they form adjacency or not? 


If OSPF-enabled routers have the same router ID, they will not form an adjacency.  The router ID in OSPF is a unique identifier for each router in the OSPF domain.  When routers attempt to form an OSPF adjacency, they exchange Hello packets  containing their router IDs.  

If two routers have the same router ID, they will consider each other as the same  router and will not form an adjacency, as OSPF requires each router to have a  unique router ID within the OSPF domain.

Q36) What is LSA in case of OSPF? It resemblance to which properties of EIGRP? 


LSA (Link State Advertisement) in OSPF (Open Shortest Path First) is a type of  packet used by OSPF routers to exchange information about the network  topology.  

LSAs contain information about routers, links, and network segments in an OSPF  domain.  

OSPF routers use LSAs to build and maintain a map of the entire OSPF domain,  which is used to calculate the shortest path to each destination network. 

LSAs in OSPF resemble the topology table in EIGRP (Enhanced Interior Gateway  Routing Protocol).  

Both OSPF LSAs and EIGRP’s topology table contain information about the  network topology and are used by routers to make routing decisions. However,  there are differences in how they are implemented and the specific information  they contain.  

OSPF LSAs are more standardized and contain specific types of information about  routers and links in the OSPF domain, while EIGRP’s topology table is more  flexible and can contain additional information based on EIGRP’s metric  calculation and route selection process. 

Q37) What are the states used in OSPF when forming neighbours ip? 🡺 

In OSPF (Open Shortest Path First), when routers are forming neighbours and  establishing OSPF adjacencies, they go through several states.  

These states are part of the OSPF neighbour relationship process and are as  follows: 

  1. a) Down: This is the initial state of an OSPF neighbour relationship. In this state, the router has not yet received any OSPF Hello packets from the potential neighbour. 
  2. b) Init: In this state, a router has received an OSPF Hello packet from a potential neighbour, but the router’s own Router ID was not included in the Hello packet’s neighbour list. 
  3. c) Two-Way: In this state, the router has received an OSPF Hello packet from a potential neighbour, and the router’s own Router ID was included in the Hello packet’s neighbour list. At this point, bidirectional communication  between the two routers is established.
  4. d) Exstart: In this state, routers are determining which router will be the master in establishing the adjacency. They exchange their initial database descriptions (DBDs) to synchronize their databases. 
  5. e) Exchange: In this state, routers exchange database description packets (DBDs) to describe their link-state databases. They request and send link state advertisements (LSAs) that are missing in their databases.
  6. f) Loading: In this state, routers request and receive missing link-state advertisements (LSAs) from each other. They are in the process of updating their link-state databases. 
  7. g) Full: This is the final state of the OSPF neighbour relationship process. In this state, routers have fully synchronized their link-state databases, and the OSPF adjacency is fully established. Routers in this state can exchange  routing updates and forward traffic based on the OSPF topology. 

Q38) How does STP maintain a loop-free network? 


STP (Spanning Tree Protocol) maintains a loop-free network by ensuring that only  one active path exists between any two network devices.  

It accomplishes this by electing a root bridge and calculating the shortest path to  the root bridge for each network segment.  

Here’s how STP maintains a loop-free network: 

  1. a) Root Bridge Election: STP elects a root bridge for the network based on the bridge ID, which consists of a priority value and a MAC address. The bridge with the lowest bridge ID becomes the root bridge. All other bridges in the  network determine their shortest path to the root bridge. 
  2. b) Designated and Non-Designated Ports: After the root bridge is elected, each network segment (or LAN segment) selects a designated port. The designated port is the port on the switch that offers the shortest path to  the root bridge for that segment. All other ports on the segment are in a  blocking state, preventing loops. 
  3. c) Blocking Ports: STP uses a blocking state on ports that are not designated Blocking ports do not forward traffic but are kept in a listening state to detect if the designated port fails. If the designated port fails, the  blocking port can transition to a forwarding state to maintain connectivity. 
  4. d) Path Cost Calculation: STP calculates the path cost for each port based on the speed of the link. Higher-speed links have lower path costs, so STP prefers these paths over lower-speed links. 
  5. e) Loop Prevention: By using the root bridge election, designated ports, and blocking ports, STP ensures that there is only one active path between any two devices in the network. This prevents loops from forming and ensures 

that traffic can flow without causing broadcast storms or other network  issues. 

Q39) What is BDPU? What is the basics function of BPDU? 


BPDU (Bridge Protocol Data Unit) is a message format used by the Spanning Tree  Protocol (STP) and its variants (RSTP, MSTP) to exchange information between  switches in a network to detect loops and create a loop-free topology.  

The basic function of BPDU is to allow switches to communicate with each other  and exchange information about the network topology. 

  1. a) Electing the Root Bridge: BPDUs contain information about the sending switch, including its bridge ID and the path cost to the root bridge. Switches use this information to elect the root bridge for the network. 
  2. b) Calculating the Shortest Path to the Root Bridge: BPDUs also contain information about the sending switch’s best path to the root bridge. Switches use this information to determine the shortest path to the root  bridge for each network segment. 
  3. c) Detecting Loops: BPDUs are used to detect loops in the network. When a switch receives a BPDU on a port, it checks the BPDU information to determine if the receiving port should be blocked to prevent a loop. 
  4. d) Notifying of Topology Changes: BPDUs can also be used to notify switches of changes in the network topology, such as link failures or topology When a switch detects a change, it sends out BPDUs to inform  other switches of the change. 

Q40) Difference between Spanning Tree Protocol (STP) and Rapid Spanning Tree Protocol (RSTP)? 


Its IEEE standard is 802.1D.  Its IEEE standard is 802.1W.
In STP only the root bridge sends  BPDU (Bridge protocol data unit) and it  is transferred by others. In RSTP all bridges can forward BPDUs.
STP has three port roles (i.e., Root  Port, Designated Port, and Blocked  Port). RSTP has four-port roles (i.e., Root  Port, Designated Port, Alternate Port,  and Backup Port).
STP has five port states (i.e.,  

Forwarding, Learning, Listening,  Blocking, and Disabled). 

RSTP has three port states (i.e.,  Forwarding, Learning, and Discarding).


It doesn’t have any link type.  It has Two link types i.e., Shared link  and Point to point link.
STP provides slower network  

convergence in response.

RSTP provides significantly faster  network convergence.


Q41) How do non root bridge decide which port will elect as root port? 🡺 

In a Spanning Tree Protocol (STP) network, non-root bridges determine which  port will be the root port based on the following criteria: 

  1. a) Path Cost: The path cost is calculated based on the speed of the link. Lower-speed links have higher path costs. The port with the lowest path cost to the root bridge is selected as the root port. 
  2. b) Bridge ID of Neighbour Switches: If there are multiple paths with the same path cost, the bridge ID of the neighbour switches is used to break the tie. The switch with the lower bridge ID is preferred, and its corresponding port  is selected as the root port. 
  3. c) Priority and MAC Address: If the bridge ID tiebreaker is not enough to select a root port, the switch’s own priority and MAC address are used as additional tiebreakers. The switch with the lower priority or MAC address is   
  4. d) Port ID: If all other factors are equal, the port ID (port number) is used as the final tiebreaker. The port with the lower port ID is selected as the root  

By using these criteria, non-root bridges in an STP network can determine the  best path to the root bridge and select the root port accordingly. This helps to  create a loop-free topology and ensures that traffic is forwarded along the most  efficient path in the network. 

Q42) How many designated ports can be available on a root bridge? 🡺 

On a root bridge in a Spanning Tree Protocol (STP) network, all ports are  designated ports.  

This means that there can be multiple designated ports on a root bridge, one for  each segment connected to the root bridge. 

A designated port is the port on a segment that offers the shortest path to the  root bridge for that segment. 

Since the root bridge is the central point in the STP topology and all other  switches in the network are trying to reach it, all ports on the root bridge will be  designated ports.  

This allows traffic to flow efficiently through the network, with each segment  having a single designated port to reach the root bridge. 

Q43) How many root bridges can be available on a STP configured network? 🡺 

In a Spanning Tree Protocol (STP) configured network, there can be only one Root  Bridge.  

The root bridge is the central bridge in the STP topology and is responsible for  providing a reference point for all other bridges in the network.  

All other bridges in the network are either directly or indirectly connected to the  root bridge. 

The root bridge is elected based on the bridge ID, which consists of a priority  value and a MAC address.  

The bridge with the lowest bridge ID becomes the root bridge. 

If multiple bridges have the same priority, the bridge with the lowest MAC  address is selected as the root bridge. 

Having only one Root Bridge ensures that there is a single point of reference for  the STP topology, which helps prevent loops and ensures that traffic flows  efficiently through the network. 

Q44) Which switching technology reduces the size of a broadcast domain? 🡺 

VLANs (Virtual Local Area Networks) are a switching technology that reduces the  size of a broadcast domain. VLANs allow you to segment a single physical network  into multiple logical networks, each with its own broadcast domain. By separating  devices into different VLANs, you can control the broadcast traffic within each  VLAN, which helps reduce the overall size of the broadcast domain and improves  network performance. 

Q45) Which protocols are used to configure trunking on a switch? 🡺 

The protocols used to configure trunking on a switch are: 

IEEE 802.1Q: This is the industry-standard protocol for trunking. It adds a 4-byte  tag to Ethernet frames, indicating the VLAN to which the frame belongs.

Cisco Inter-Switch Link (ISL): This is a proprietary protocol developed by Cisco  before 802.1Q became the standard. ISL encapsulates the entire Ethernet frame  with a header and trailer, adding VLAN information 

Both protocols allow switches to carry traffic from multiple VLANs over a single  link, known as a trunk. However, 802.1Q is more commonly used today due to its  standardization and compatibility with non-Cisco devices. 

Q46) What is meant by “router on stick”? 


“Router on a stick” is a network configuration where a single physical router  interface is used to route traffic between multiple VLANs (Virtual Local Area  Networks). In this configuration, the router interfaces are configured as trunk  ports, allowing them to carry traffic for multiple VLANs over a single physical link. 

The term “router on a stick” comes from the idea that the single physical link  resembles a stick, with the router acting as the “router” that routes traffic  between VLANs. 

To implement router on a stick, the router interface connected to the switch is  configured with sub interfaces, each corresponding to a different VLAN. Each sub  interface is assigned an IP address in the respective VLAN’s subnet, and the router  uses 802.1Q trunking to tag traffic from each VLAN as it travels over the single  physical link. This allows the router to differentiate and route traffic between  VLANs. 

Q47) Which are the two trunking protocols? 


The two trunking protocols commonly used in networking are: 

  1. IEEE 802.1Q: This is the industry-standard trunking protocol used to carry VLAN information on Ethernet networks. It adds a 4-byte VLAN tag to the Ethernet frame, allowing switches to identify which VLAN the frame  belongs to. 
  2. Cisco Inter-Switch Link (ISL): This is a proprietary trunking protocol developed by Cisco. ISL encapsulates the entire Ethernet frame with a header and trailer, adding VLAN information. However, ISL is less  commonly used today as 802.1Q has become the industry standard.

Q48) How does a switch forward traffic from a trunk port to appropriate VLAN? 


When a switch receives traffic on a trunk port, it uses the VLAN tag in the  Ethernet frame’s header to determine which VLAN the traffic belongs to. 

Here’s how a switch forwards traffic from a trunk port to the appropriate VLAN: 

  1. a) Receive Frame: The switch receives an Ethernet frame on a trunk port. The frame includes a VLAN tag, which indicates the VLAN to which the frame  
  2. b) Check VLAN Tag: The switch checks the VLAN tag in the frame’s header to determine the VLAN ID.
  3. c) Look up VLAN Membership: The switch looks up the VLAN ID in its VLAN database to determine which ports are members of that VLAN.
  4. d) Forward Traffic: If the frame is destined for a device within the same VLAN, the switch forwards the frame out the appropriate access port for that If the frame is destined for a device in another VLAN, the switch  forwards the frame out the trunk port with the appropriate VLAN tag. 

Q49) What are different Vlan modes? 


In Cisco switches, there are several VLAN modes that determine how a port  behaves in relation to VLANs. The main VLAN modes are: 

  1. a) Access Mode: This mode is used for connecting devices that are not VLAN aware. Traffic received on an access port is untagged, and the switch forwards it to the VLAN configured on the port. The switch discards any incoming frames with VLAN tags. 
  2. b) Trunk Mode: Trunk mode is used for interconnecting switches or connecting to VLAN-aware devices. Traffic on a trunk port is tagged with the VLAN ID, allowing multiple VLANs to be carried over the same physical   
  3. c) Dynamic Auto Mode: In this mode, the port is willing to form a trunk if the neighboring switch is set to trunk or dynamic desirable mode. If the neighboring switch is set to access or dynamic auto mode, the port  becomes an access port. 
  4. d) Dynamic Desirable Mode: In this mode, the port actively tries to form a trunk with the neighboring switch. If the neighboring switch is set to trunk, dynamic auto, or dynamic desirable mode, a trunk will be formed. If the  neighboring switch is set to access mode, the port becomes an access port.
  5. e) Nonegotiate Mode: This mode disables DTP (Dynamic Trunking Protocol) negotiation on the port, forcing it to become a trunk port if the neighboring switch is set to trunk or dynamic desirable mode. 
  6. f) Default Mode: The default mode for Ethernet ports on Cisco switches is dynamic auto, while the default mode for Fast Ethernet and Gigabit Ethernet ports is dynamic desirable. 

Q50) What are the requirements to exchange VTP messages between two switches? 


To exchange VTP (VLAN Trunking Protocol) messages between two switches, the  following requirements must be met: 

  1. a) VTP Domain Name: Both switches must be configured with the same VTP domain name. The VTP domain name is a case-sensitive alphanumeric string that identifies the VTP domain to which the switch belongs. 
  2. b) VTP Mode: At least one of the switches must be in VTP server or transparent mode. The VTP server is responsible for managing VLAN information and propagating it to other switches in the same VTP domain.  The other switch can be in server, client, or transparent mode. 
  3. c) VTP Version: Both switches must be using the same version of VTP (either VTP version 1 or VTP version 2). VTP version 2 introduces enhancements over version 1, such as support for Token Ring VLANs and better handling  of VLAN pruning. 
  4. d) Trunk Link: The switches must be connected by a trunk link that allows VLAN traffic to pass between them. The trunk link should be configured to allow the necessary VLANs to pass. 
  5. e) Configuration Revision Number: The switch with the higher configuration revision number will overwrite the VLAN configuration on the switch with the lower revision number. Therefore, it’s important to ensure that the  configuration revision numbers are synchronized between switches. 
  6. f) VTP Password (Optional): If a VTP password has been configured on the switches, it must be the same on both switches. The VTP password is used to authenticate VTP messages exchanged between switches. 


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