Category: CCNA

    What is VLAN (Virtual Local Area Network)?

    VLAN (Virtual LAN) by IEEE stands for Virtual Local Area Network. It works on the 2nd layer of OSI. Using this technology, network users and resources on a local area network (LAN) are logically grouped and assigned to ports. These logical networks are split broadcast domains. After configuration, since each Virtual LAN receives only its own broadcast, broadcast traffic is reduced and bandwidth is increased. When it is desired to create a different VLAN on the LAN, the empty ports of the switch used can be used. This saves network investment.

    Segmenting the network using Virtual LAN enables us to manage users more easily, to configure and implement access permissions more easily, and to identify and resolve potential network problems.

    Including a guest user in the system network may not be safe for security. For this reason, it will be safer to take the guest user to the internet environment via a bent network isolated from the system. This is by dividing the network, that is, by configuring the VLAN. In a network, users in VLAN can only communicate with each other, they cannot communicate with users in a different VLAN.

    It is done by logically grouping network users and resources on a local area network (LAN) and assigning them to ports on the switch. Since each VLAN will only receive its own broadcast, the bandwidth is increased by reducing broadcast traffic. Virtual LAN definitions can be defined according to location, department, people or even the application or protocol used.

    First of all, let’s talk about a few benefits of configuring it on the network you work with.

    • Reduces the traffic by minimizing the mess caused by broadcast messages in the local network.
    • To obtain a more manageable network by assigning at least one VLAN to each unit on the local network.
    • To secure the network by determining the communication (ip-routing) between VLAN blocks.
    • To provide the transmission of many VLAN-networks on the fiberoptic or UTP uplink lines with the Trunk method.

    These are the first pluses that come to mind about the benefits of VLAN. While taking precautions with firewalls against possible attacks and attacks from outside, VLAN configuration and authorization will be the first priority for internal threats.

    By applying Virtual LANs on the network, many problems caused by 2nd level switching are eliminated. We can basically collect them under 3 headings.

    Broadcast Control

    Broadcast is produced by every protocol. However, its density varies depending on the protocol, application and how the service is used. In level 2 switching devices that are used flat, the incoming broadcast packet is sent to each port regardless of whether the end users can receive it. The high number of devices on the network causes the broadcast to increase exponentially and send these packets to every device on the network.

    A well-designed network should be segmented according to criteria. The most convenient way to do this is through switching and routing. This prevents broadcast traffic between VLANs.

    Security

    Another disadvantage of a flat network without a VLAN is security. On a network that does not use a switch (via distribution coax cable or hub), the data flow between the two computers is transmitted to all devices connected to the network (collision). This causes traffic problems and is quite unsafe due to software and even hardware that listens to all packets passing on the network and decodes the data part. When a switch is used as a distribution device, this port can be prevented by separating each port into its own collision segment. However, the fact that broadcast is sent to all ports in the switch topology used flat means that all devices on the network receive each other’s broadcast traffic.

    A second point is that access to other groups of users on the network that will not have a network relationship with others is provided and broadcast packages are sent. When the network devices on the switch are divided into VLANs, such vulnerabilities will be eliminated. In this way, a user will not be able to connect to any end on the network and listen to the entire network and gain information. However, it will be able to operate on the VLAN it will be connected to.

    Flexibility

    Broadcast groups were actually created on a network created by creating VLANs. Regardless of its physical location on the switches, you have the flexibility to assign a user to the VLAN you want. Likewise, a growing VLAN over time can be transferred to newly created VLANs. This is possible with a new port definition on the switch.

    When the same operation is attempted without using Virtual LAN support, the connection to the central router should be physically provided for the new subnet to be created.

    A router or another layer 3 devices is required for routing between VLANs. One end must come from the switch to the router for each VLAN used on the switch.

    Relationships Between VLANs

    There are two types of VLANs.

    1. Static VLANs: They are defined by the network administrator and assigned on switch ports. Unless the port of the switch is changed by the administrator again, it belongs to the Virtual LAN. This method simplifies network management and monitoring. In other words, interfaces of uplink ports in SVLAN configuration are tagged to the desired IDs (Tagged). In the interfaces of other user ports, the label for the VLAN that it will be a member of is removed (Untagged). Therefore, the user using that port will be able to exit only that block of IP, whichever tag is removed from the system administrator.

    Finally, all switches, modems, firewalls, routing and monitoring servers in our network must be members of the VLAN-100, which is the “Network Management VLAN”. It will use this VLAN-100 network when communicating among themselves.

    2. Dynamic VLANs (DVLAN): It recognizes the DVLAN of the device connected to the switch port in the DVLAN and automatically assigns that port to the DVLAN it recognizes. DVLAN identification can be made on the basis of hardware address (MAC), protocol or even application with network management programs. For example; Suppose MAC addresses are entered into a central VLAN management application. When a device is connected to a switch on the network to a port that does not have a VLAN assigned, the MAC address is asked to the VLAN management database and the received VLAN value is assigned to that port of the switch.

    If the user changes or the device connected to the terminal changes, the new VLAN value is requested and assigned to the port. In this case, after the database is carefully prepared, the management and configuration work of the network administrator is reduced. It provides the map database service for VMPS MAC addresses for DVLAN use on Cisco devices. In other words, in DVLAN configuration, the uplink ports on the switch are tagged as in the static configuration.

    However, all of the user ports are members of the Virtual LAN of the guest network. With the combination of switch-firewall or switch-DHCP server, thanks to the user mac address, the user is automatically registered to that VLAN. The authorization process is performed between the switch and the DHCP server and the ID of the user computer is sent to the switch and the switch makes this port a member of the VLAN that DHCP requests. This process can be either Computer-defined or user-defined. This is also possible thanks to the switch-DHCP server-active directory server trilogy. If your company has public computers and you want to authorize them according to the users, you can solve it in this way. Thus, VLAN-10 will be automatically authorized in the network if the accountant opens computer A, VLAN-40 if the engineer opens, or VLAN-200 if our guest opens.

    VLAN Definitions

    VLANs are distributed among connected switches. The package received by the switch is sent to the ports assigned to the VLAN to which it belongs by the method called “frame tagging”. A switch is a group of switches that carry the same information. There are two types of connections in these devices.

    Access links; is a connection that belongs only to a VLAN. The device connected to an access link operates on the assumption that it is connected to a broadcast group regardless of the relationships between VLANs and the physical networks. Switches remove the header on the package before sending it to the device connected with the access link. The packets sent by the devices on the access link cannot talk to devices other than their VLANs unless directed by a router or another 3rd layer device.

    Trunk links; can carry multiple VLANs on it. It can be made from the Trunk link switch to another switch, a router or a server. It has support only on Fast or Gigabit Ethernet. Cisco switches use two different methods to recognize VLANs on a trunk connection: ISL and IEEE802.1q. Trunk connections are used to move VLANs between devices and can be formatted to carry all or part of the VLANs.

    In the frame tagging method, the switch from which the package comes from recognizes the VLAN ID (VLAN number) of the package and finds out what should be done from the filter table to the package. The VLAN header on the packet leaves the packet before leaving the trunk link. If there is another trunk connection on the switch from which the pack came, the packet is sent directly through this port. The last device that the packet will reach cannot access the VLAN information on the packet.

    VLAN Identification Methods

    Inter-Switch Link (ISL): It is used by Cisco switches and can only work on Fast or Gigabit Ethernet. This method is called “external tagging”, which does not change the original size of the package, but adds a 26 byte ISL header to the package, allowing VLAN recognition between devices. It also adds a 4-byte length FCS (frame check sequence) field that controls the pack to the end of the packet. The package can only be recognized by devices that recognize ISL after these plugins. The size of the pack can reach up to 1522 bytes so that the maximum length in the ethernet network is 1518 bytes. When the package that is enveloped with ISL information, the access link type is going to be connected, it is separated from all its plugins and returns to its original form.

    IEEE 802.1q: This standard method developed by IEEE is used to carry multiple VLANs between different brands of switches or routers over a connection. A suitable header is placed on the incoming packet according to the defined standard and the VLAN of the packet is recognized among the devices.

    LAN Emulation (LANE): It is used to carry multiple VLANs over a connection in the ATM network.

    IEEE 802.10 (FDDI): It is used to carry multiple VLANs over a connection in the FDDI network. It adds a VLAN identification header called SAID to the package.

    Routing Procedures Between VLANs

    Devices connected to a VLAN can talk freely among themselves and send their broadcasts. VLANs divide the network and separate the traffic. A 3rd layer device is required for devices to talk between VLANs.

    In this case, there are two options:

    1. A connection is added for each VLAN on a router and the necessary configurations are made on the router and communication between the VLANs is provided.

    2. Connection to switch fabric is made on a router that can define VLAN on ISL (or trunk connection), communication between VLANs is provided after necessary configurations.

    If the number of VLANs to be defined on the network is small, a router with a number of VLAN outputs is provided by choosing the first option.

    However, if the number of VLANs is high and the network is open to expansion, the second option should be preferred. Cisco routers provide ISL support in 2600 and later models. In this case, ISL service is run on a connection of the router (preferably the one with the highest bandwidth) or routing is provided by providing a “route switch module (RSM)” on the router. RSM provides 1005 VLAN support and packet processing is less time since it works on the router’s backplane. VLAN routing is called “router-on-a-stick” by running ISL on the router’s Fast or Gigabit Ethernet connection.

    VLAN Trunk Protocol (VTP)

    Cisco created the VLAN Trunk Protocol (VTP) protocol for VLAN management of connected switches on the network. It enables the VTP network administrator to perform operations such as changing, adding, deleting names on VLANs and notifies new information to all switches on the network. VIP; With multi-switch networks, central management eliminates errors such as lack of configuration and inaccuracy. It enables the establishment of VLAN trunk connections between different networks. For example, Ethernet shares the VLAN definitions between ATM (LANE), FDDI. It allows VLAN monitoring and monitoring without errors. It reports dynamically added VLANs to all switches.

    In order to manage VTP on the network, a VTP server must serve the network. All servers and switches to which the information is to be shared must be formatted into the same VTP domain group. Switches broadcast VTP domain information, configuration renewal number and all known VLANs with their parameters. Switches can be set to send VTP information via trunk port, but not receive it and not update the VTP database (transparent mode).

    Switches listen to upcoming VTP information, get the definition of new VLAN, and wait for new information about this VLAN from trunk ports. The VTP information that can come from can be ID, IEEE 801.10, SAID or LANE. Updates are provided by increasing the configuration renewal number. When the switch receives a higher configuration renewal number from it, the switch knows that a newer configuration has arrived and saves the new incoming information on the old database.

    There are three types of VTP operating modes: Server, Client, Transparent.

    Server; It comes preinstalled on the Cisco Catalyst series switches. At least one VTP server is required for adding, removing, and configuring VLANs for each VTP domain. Any changes made on a switch running in server mode are announced to that VTP domain. Its configuration is stored on NVRAM (Non-Volatile RAM – Nonvolatile memory).

    Client; These are switches that receive information from VTP servers, receive and send update information, but cannot make any changes. Its configuration is not stored on NVRAM (Non-Volatile RAM – Nonvolatile memory), it is temporary.

    transparent; These are the switches that send the incoming VTP information exactly through the trunk ports without joining the VTP domain group. They do not forward any changes that can be made to the VTP database on them through trunk ports. Its configuration is stored on NVRAM (Non-Volatile RAM – Nonvolatile memory).

    Prunning

    It is changing the VTP configuration to reduce broadcast, multicast, and other unicast packets in order to save bandwidth. VTP pruning service sends the incoming broadcast to trunk ports that need to receive that information, not to others. For example; VLAN 5 broadcast, which comes to a switch that does not have any port of VLAN 5, is not sent over any port of the switch. It comes off in VTP pruning switches. In order to activate VTP pruning, it must be activated on all VTP domains. VLAN 2-1005 is pruning configurable VLAN numbers. Since VLAN 1 is a management VLAN, it can never be pruned.

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    What is Spanning Tree Protocol (STP)?

    Spanning Tree Protocol (STP) is an IEEE 802.1 standard and blocks some ports to keep only one active link between any LAN segment (collision domain) using the software-based spanning-tree algorithm on all bridge devices, including switchers. It also prevents cycles that may occur with multiple active paths between stops.

    The Spanning-tree algorithm is used in bridge and switcher-based networks and decides the best way traffic can travel from source to destination. This algorithm takes into account all backup paths and activates only one of them at any time.

    For networks where the Spanning-tree Protocol is actively used, one root bridge per root network (the root bridge), one non-root bridge (root port) for each non-root bridge, and traffic to pass through each segment. there is one designated port.

    Some Spanning Tree Terms

    • Bridge ID: The MAC address of the switcher is its bridge ID. It is important for root bridge selection in the network.
    • Non-root Bridge: All other bridges, except the root bridge, are non-root bridges.
    • Root Port: The root port is always the port that is directly connected to the root bridge or closest.
    • Designated Port Cost: If there is more than one root connection between two switchers, it is taken into consideration. It is calculated by looking at the bandwidth.
    • Bridge Protocol Data Unit (BPDU): All switchers and bridges included in the spanning-tree protocol in the same local area network (LAN) communicate with each other with BPDU messages. BPDUs are; It includes information such as the switcher’s priority, port priority, port value, MAC address. The spanning-tree protocol also uses this information when selecting the root bridge, root port, and assigned port.
    • Convergence: Convergence occurs when all the ports of the switchers and bridges go from the blocking state to the transmission state. Data is not transmitted until convergence is complete. All devices need to be updated before data can be transmitted again. Convergence is important to ensure that all devices have the same database, but it takes some time.

    Root Bridge Selection

    The root bridge is the logical center of spanning-tree topology in switched networks. Each bridge on topology sends messages called “hello BPDU” to each other and claims that it is the root. In these messages;

    • The identity of the root bridge (BID): This value is its own ID, as each bridge initially shows itself as the root bridge.
    • Priority: It belongs to the root bridge. Again, this value is its priority, as every bridge shows itself as the root bridge.
    • Cost of reaching the root: Initially zero.

    The root with the lowest priority in the root bridge selection process. If the priorities are equal, the root with the lowest ID will be.

    All other switchers and bridges in the network are called non-root bridges.

    BandwidthSTP Cost
    4 Mbps250
    10 Mbps100
    16 Mbps62
    45 Mbps39
    100 Mbps19
    155 Mbps14
    622 Mbps6
    1 Gbps4
    10 Gbps2

    Responses to Network Exchange

    Root bridges send the “hello” BPDUs they send every two seconds to indicate that they are working. All other switchers and bridges receive these BPDUs. If “Hellos” come from the path where the data is moved, the path to the root is still standing. Spanning-tree operation starts again if there is a wait in receiving “hello”. “Hello” BPDU defines the time that bridges should wait while responding to the network change. These times are; “Hello Time” is the longest waiting time (max-age) and forward delay.

    • “Hello Time”: Indicates how often the root will send periodically “hello” BPDUs to be transmitted by bridges/switch in succession. The default duration is 2 seconds.
    • Longest Waiting Time: It is the time that the switch/bridges have to wait for the STP to change the topology after hearing the “hello”. The default duration is 20 seconds.
    • Transmission Delay: The time it takes for the interface to change from the blocking state to the forwarding state.

    STP operation in a stable network works as follows:

    1. The root sends “hello” BPDUs from all its interfaces. (The cost of these BPDUs is 0.)
    2. Neighbor switch/bridges add and transmit “hello” BPDUs to their cost from non-root designated ports.
    3. Repeats step 2 when each switch/bridge “hello” in the network receives the BPDU.
    4. Each bridge repeats step 1 at every “hello time”
    5. If a bridge/switch did not receive “hello” BPDU during the “hello time” period, it continues to operate normally for the longest waiting time, if it still does not receive the BPDU, the STP reacts to change the topology.

    The Mission of the Spanning Tree Protocol

    The Spanning-tree algorithm brings each bridge and switcher port to one of the blocking or transmission states. These port states;

    Blocking state: Frame cannot be sent or received from ports, it only listens to BPDUs. The purpose of this situation is to prevent the formation of loops. When the switchers are operated, all ports are in the blocking state by default.

    Listening State: Ports listen to BPDUs before passing the frames to ensure that no looping occurs in the network. While the ports are in this state, they are prepared to transmit data without preparing the MAC address table.

    Learning State: The ports listen to BPDUs and learn all the paths in the network. Ports in this state begin to form the MAC address table, but do not transmit frames yet.

    Forwarding State: The ports are considered to be in an active spanning-tree. All of the transmission ports can receive and send frames.

    Disable State: The passive state does not participate in frame transmission and STP.

    Spanning Tree Port States

    Ports on Bridge and switchers running STP switch between five different states.

    Blocking State: The port in the heap state does not transmit frames, it only listens to BPDUs. The purpose of this situation is to prevent the formation of loops. By default, all ports are heaped when switchers are operated.

    Listening State: Ports listen to BPDUs before passing the frames to ensure that no looping occurs in the network. While the ports are in this state, they are prepared to transmit data without preparing the MAC address table.

    Learning State: The ports listen to BPDUs and learn all the paths in the network. Ports in this state begin to form the MAC address table, but do not transmit frames yet.

    Forwarding State: The port both sends and receives all data frames.

    Passive (Disable): The passive (administrative) port does not participate in frame transmission and STP.

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    Cisco Router Boot Process

    A router initially loads the following two files into RAM:

    IOS image file: IOS simplifies the basic operation of the device’s hardware components. The IOS image file is stored in flash memory of router.

    Initial configuration file: The initial configuration file contains commands that are used to perform the initial configuration of the router and to create the running configuration file stored in RAM. The initial configuration file is stored in NVRAM. All configuration changes are stored in the running configuration file and in the IOS.

    The running configuration is changed when the network administrator performs the device configuration. When changes are made to the running-config file, it must be saved to the NVRAM as the initial configuration file if the router restarts or shuts down.

    Router Boot Process

    The boot process consists of three main steps:

    1. Performs POST and loads the boot program.
    2. Find and install the Cisco IOS software.
    3. Locates the initial configuration file, loads it, or enters setup mode.

    1. Power-on Self-Test (POST) is a common process that occurs on almost any computer at startup. POST is used to test the router hardware. When the router is turned on, the software in the ROM chip runs POST. During this self-diagnostics, the router works with the ROM diagnosis of various hardware components including CPU, RAM, and NVRAM. When POST is finished, the router runs the boot program.

    After POST, the boot program is copied from ROM to RAM. After entering the RAM, the CPU performs the instructions of the boot program. The main task of the boot program is to find the Cisco IOS and install it in RAM.

    Note: If there is a console connection to the router, the results appear on the screen.

    2. Typically, IOS is stored in flash memory and copied to RAM for CPU operation. During the self-decompression of the IOS image file, a symbol sequence is displayed.

    If the IOS image is not in flash memory, the router can search with the TFTP server. If a full IOS image is not found, a reduced version of the IOS from the ROM is copied to RAM. This version of IOS is used to help diagnose any problem and can be used to install the full version of IOS into RAM.

    3. The bootstrap program then looks for the initial configuration file (also known as “startup-config da) in NVRAM. The file contains previously saved parameters and configuration commands. If so, it is copied to RAM as a running configuration file or “running-config”.

    The Running-config file contains interface addresses, initiates routing, configures router passwords, and defines other device properties.

    If the start-config file is not present in the NVRAM, the router can search for a trivial file transfer protocol (TFTP) server. If the router detects an active connection to another configured router, it sends a broadcast to search for a configuration file over the active connection.

    If a TFTP server is not found, the router displays the request to enter setup mode. The setup mode consists of a series of questions that ask the user for basic configuration information. Setup mode is not designed to enter complex router configurations, and network administrators normally do not use it.

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    What is ARP in Networking and How it Works?

    For IPv4 addresses to resolve to MAC addresses, the frames to be placed in a LAN environment must be the destination MAC address.

    When a packet is sent to the data link layer to be enclosed in a frame, the node queries a table in its memory to find the address of the data link layer assigned to the destination IPv4 address. This table is called the ARP table or ARP cache. The ARP table is stored in the RAM hardware of the device.

    Each entry or row in the ARP table links an IP address to a MAC address. The relationship between the two values ​​is called a map, which means that you can find an IP address in the table and find the corresponding MAC address. In the ARP table, device assignments are temporarily stored (cached) in the local LAN.

    To begin processing, a transmitting node attempts to find the MAC address assigned to an IPv4 destination. If this map is found in the table, the node uses the MAC address as the target MAC in the frame that contains the IPv4 packet. The frame is then encoded in the network environment.

    Understanding ARP (Address Resolution Protocol)

    The ARP table is maintained dynamically. There are two ways in which a device can collect MAC addresses. The first is to monitor the traffic that occurs in the segment of the local network. Because a node receives frames from the media, it can save the source IP and MAC addresses as mappings in the table. When frames are transmitted on the network, the device completes the ARP table with address pairs.

    A device can also receive address pairs by sending an request as shown in the figure. An ARP request is a Layer 2 broadcast transmitted to all devices on an Ethernet LAN. The ARP request includes the IP address and the broadcast MAC address of the target host, FFFF.FFFF.FFFF. Because it is a broadcast, all nodes in the Ethernet LAN receive and examine the content. The IP address responds to the node that matches the IP address in the request. The response is a unicast frame containing the MAC address corresponding to the IP address in the request. This response is used to create a new entry in the ARP table of the sending node.

    The entries in the ARP table have a timestamp similar to the MAC table entries in the switches. If a device does not receive a frame from a particular device before the time stamp expires, its entry is removed from the table.

    Additionally, static assignment entries can be entered in an table, but this is not very common. Static entries in the ARP table do not expire over time and must be manually removed.

    How Does ARP Protocol Work?

    What does the node do when a frame needs to create a frame and the ARP cache does not include an IP address assigned to a destination MAC address? When the ARP receives a request to map an IPv4 address to a MAC address, it searches for the map stored in the table. If no input is found, IPv4 packet encapsulation is not performed, and Layer 2 operations notify the ARP that a map is needed.

    The ARP then sends an request packet to find the MAC address of the target device of the local network. If a device receiving the request has a destination IP address, it responds with an response. A map is created in the table. Packets of this IPv4 address can now be placed in frames. If no device responds to an request, the packet is discarded because no frames can be created. This encapsulation error is reported to the upper layers of the device.

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    What is CCENT (Cisco Certified Entry Network Technician)?

    What is Cisco CCENT?

    The Cisco Certified Entry Network Technician (CCENT) Certificate supports the ability to set up, run, and resolve a small enterprise network, including a basic security network. Professionals with this certificate have the skills necessary for basic network support positions.

    This certificate includes:

    1. Basic elements of the network
    2. WAN technologies
    3. Basic security
    4. Wireless concepts
    5. Routing Basics
    6. Simple Network Configuration

    The CCENT Certificate is the first step at Cisco to obtain the CCNA Certificate covering the networks of more complex companies.

    It is intended for students at Cisco Networking Academy in the ICT industry looking for entry-level jobs or waiting to meet their base requirements to acquire more specialized ICT skills.

    The preparation of this certification consists of two courses:

    Introduction to networks

    • Network scanning
    • Setting up a network operating system
    • Network protocols and communication
    • Network access
    • Ethernet
    • Network layer
    • Transport layer
    • IP Address Assignment
    • IP network section on subnets
    • Application layer
    • This is a network

    Basic Routing Policies

    • Introduction to switched networks
    • Configuration and basic switching concepts
    • VLAN
    • Routing Concepts
    • VLAN communication
    • Static routing
    • Dynamic routing
    • OSPF single area
    • Access Control Lists
    • DHCP
    • Network address translation for IPv4

    The exam corresponding to this certificate is 100-001 Interconnection Cisco Networking Devices Part 1 (ICND1). Evaluate the ability to set up, run and solve events in a small network.

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    What is CCNA (Cisco Certified Networking Associate)?

    For basic network engineers, CCNA stands for Cisco Certified Network Associate, a certification program that helps you increase your investment in basic network knowledge and increases the value of your employer network.

    CCNA Certification verifies the establishment, configuration, operation, and troubleshooting of medium-sized routers and switching networks, including the implementation and verification of connections to remote sites in a WAN.

    To obtain a CCNA header and certification change, you will need to obtain an approval score on the Cisco # 200-120 exam or by combining both Cisco Network Device Interconnection approval.

    Pass the ICND1, which validates the knowledge and skills required to set up and issue a CCENT certificate, which means the Cisco Certified Entry Network Technician. Confirmation scores are determined by statistical analysis and may vary.

    At the end of the exam, the candidates receive a final report as well as the loss of responsibilities for the exam section and the passing score of the exam. CCNA does not publish an exam on approval points due to exam questions, and approval points are subject to change without notice.

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    What is Cisco CCNA Certification and What are its Advantages?

    We make it clear that Cisco is a leading communications company in the world of data and IT networks, a very important company that manufactures network components such as routers, hardware firewalls, IP telephony products.

    Cisco Systems offers a range of training programs that ensure the training and certification of professional in the IT and computer networks field.

    Cisco Certifications are internationally recognized and have become a standard for communications, providing great reliability and a high reputation.

    The certificates are shown in the following list range from lesser to more complex, starting with CCENT:

    CCENT (Cisco Certified Entry Network Technician):

    This is your first step towards CCNA certification and will help you stand out from the crowd in entry-level positions. Having CCENT means you have what it takes to manage a small business branch network.

    CCNA (Cisco Certified Networking Associate):

    One of the most important certificates in the IT industry. This certificate represents the relevant level for practical skills in diagnosing and resolving specific network problems.

    CCNP (Cisco Certified Network Specialist):

    Provides knowledge and practical experience to design and support complex business networks in the real business environment, these skills are equally important in today’s physical networks and virtualized network functions.

    CCIE (Cisco Certified Internet Specialist):

    Evaluates infrastructure network design skills at the level of experts worldwide. This certification is recognized worldwide as the most prestigious network certificate in the industry.

    Cisco Certified Architect:

    The highest-level certification within the Cisco certification program. Top of the pyramid for those who want to verify Cisco technology and infrastructure architecture.

    Now, this point has been clarified, let’s focus on the main topic and advantages of CCNA, but before I remember that CCNA Routing and Switching certification is valid for three years. After this time, you will need to re-certify for CCNA or higher levels.

    A professional with Cisco CCNA Routing and Switching certification has the knowledge to set up and configure the network infrastructure that connects all devices within a company.

    Some of its advantages:

    • It is one of the most recognized certificates in the IT sector.
    • It is an important step to building a career in IT, so you can prepare for a successful career in networking.
    • You can earn much more money than you currently receive.
    • Practical information about routing, switching, network applications, protocols, and services.
    • This certification helps you achieve a better job, becoming a certified professional becomes a more attractive candidate for the position you want to do within the company.
    • Prestige offers both you and your company a high level of information guarantee.

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    What is IGRP (Interior Gateway Routing Protocol)?

    IGRP Protocol

    IGRP (Interior Gateway Routing Protocol) is an advanced distance-vector protocol developed by Cisco Systems in the mid-1980s, including some of the RIP errors.

    Different bandwidths can be used to configure the metric value, such as the user’s network latency, bandwidth, and latency depending on the relative speed and capacity of the interface.

    The load and reliability features are calculated based on the performance of the interface in actual network traffic management, although they are not enabled by default for routing decisions.

    Like RIP, it uses IP broadcasts to forward routing information to neighboring routers. However, IGRP has been designated as its transport layer protocol.

    To transmit network route information, UDP see is not connected to TCP. Since IGRP does not have a feedback mechanism, it works in a similar way to UDP.

    It offers three major improvements over the RIP protocol. First, the IGRP metric can support a network with a maximum of 255 router hop counts. Second, the IGRP metric can differentiate between the costs associated with sees of different types of connection media. Third, it should not wait for regularly scheduled times for updates, but rather by sending information about changes in the network when it becomes available.

    IGRP is a routing protocol based on distance vectors developed by CISCO.

    Improved Scalability

    On larger networks, routing has a maximum number of 100 hops by default but can be configured with 255 hops.

    Sophisticated Matrix

    A composite metric for greater flexibility in route selection. Interconnection delay and bandwidth are used and other parameters such as reliability, load and MTU can be included.

    Multiple Rotate support

    It can hold six different cost paths between source and destination networks. Various routes can be used to increase the available bandwidth or provide route redundancy. IGRP allows triggered updates.

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    Source: https://www.cisco.com/c/en/us/support/docs/ip/interior-gateway-routing-protocol-igrp/26825-5.html

    What is OSPF (Open Shortest Path First) Protocol

    Open Shortest Path First Protocol

    OSPF is used inside the networks as RIP, the operation is very simple. Each router knows the nearby routers and the addresses each router has. In addition, each router (measured on routers) knows how far each router is. So when you need to send a packet, you send it the same way you have to do fewer skips.

    For example, a router with a local network with one workstation, and a router with three network connections (A) with a fast 48Mbps square relay network and a 64Kbps ISDN (B) line. Three packets from the local network to A and B to two packets go to W. The packet passes through B regardless of the saturation of the line or the bandwidth of the line.

    OSPF Types

    Undoubtedly, OSPF is a complex protocol and requires a lot of work to understand how it works, and makes many practices to master. One of the most important concepts in OSPF is the design and operation of different areas, which is quite confusing when this protocol is known.

    To explain how each works, it is necessary to know the types of LSA (Link State Ads) that the OSPF uses to communicate between neighbors and transmit routing information between them.

    Type 1 (LSA Router)

    Each router in area X sends a type 1 LSA to its neighbors. This LSA never leaves the domain to which it belongs and contains the Router ID of the sender and all connections that connect it.

    Type 2 (Network LSA)

    Sent by the DR (Private Router) within the network. Tells others the networks and masks it is connected to. This LSA never leaves the area it corresponds to. So, an ABR does not transmit to another region.

    Type 3 (Summary LSA)

    They are sent by an ABR to transfer information from one region to another. OSPF calls them a “summary”.

    Type 4 (ASBR-Summary LSA)

    Represents an ASBR (Autonomous System Border Router)

    Type 5 (External LSA)

    Represents an external route redistributed from another protocol within the OSPF (Ex: EIGRP). The ASBR takes the route from the external protocol and transmits them as type 5 to all internal areas except Stub type.

    Type 7

    OSPF rules say that redistribution is required only in a Spine zone (Area 0). In an NSSA domain, a router with a connection to another external routing protocol (eg RIP) can be connected and the ASBR sends these networks in type 7 format so that the ABR receives them and redistributes them as type 5.

    Type 1 and 2 LSAs are found in all areas and are not shipped anywhere they belong. Other LSAs are sent between fields, depending on the function they perform.

    Field Types

    • Standard
    • Backbone (Area 0)
    • Stub Area
    • Totally Stubby Area
    • Not-so-stubby Area (NSSA)
    • Totally Stubby NSSA

    Standard

    This is the default field and allows links to be updated, summary paths, and external paths.

    Backbone (Area 0)

    OSPF is the main area of ​​topology. It must be present and all others must depend on it. The field is labeled 0 and has the same properties as a standard field.

    Stub Area

    Such a field does not accept information about external routes to the autonomous system (redistribution), such as paths from non-OSPF sources. If routers need to route to networks outside the autonomous OSPF system, they use a default route (0.0.0.0/0) sent by ABR to other internal routers in the Stub area. ASBR is not allowed in this area (unless ABR is also an ASBR)

    Totally Stubby Area

    This area belongs to Cisco and does not accept routes from external autonomous systems (redistribution) or abstracts from other internal regions of the autonomous system. As with the Stub fields, ABRs send a default route for all external and SUMMARY routes (this is the difference with Stub). ASBR is not allowed in this area (unless ABR is also an ASBR)

    Not-so-stubby Area (NSSA)

    Almost the worst name in the world chose this name. There are type 7 LSAs in this field, which are similar to the Stub field because they do not accept information from external routes to the autonomous system (OSPF world) and replace them with a default route originating from ABR. However, the difference is that the NSSA accepts an ASBR directly connected to another routing protocol (eg, RIP, EIGRP, etc.). The NSSA ASBR transmits pathways within the site as LSA 7, and the corresponding ABR converts them to type 5 for normal treatment.

    Totally Stubby NSSA

    If the old is almost the worst name, make sure it is the worst. Fully Stubby Not Left-Handed Area or Fully Stubby NSSA is a proprietary Cisco area that functions in the same way as the Fully Stubby Area, does not allow external or summary routes, but permits an ASBR such as NSSA.

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    Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/xe-16/iro-xe-16-book/iro-cfg.html

    What is EIGRP (Enhanced Interior Gateway Protocol)?

    What is EIGRP?

    The distance vector protocol is an elegant version of the IGRP with the sole purpose.

    It has the following features:

    • RTP Yes (Trusted Transport Protocol)
    • Maintains limited updates
    • Broadcast update algorithm (DUAL)
    • Establishing contiguities
    • Preserves topology or neighboring tables

    Data in an EIGRP message is included in a TLV-style data field (Type, Length, Value).

    EIGRP Multiprotocol

    EIGRP is capable of routing different protocols, some examples:

    • IP
    • IPX
    • Apple Talk

    This is due to the use of individual protocol modules (PDMs), which are responsible for routing tasks specific to each network layer protocol.

    For example:

    The IP-EIGRP module is responsible for sending and receiving IP-coated EIGRP packets and using DUAL to create and maintain the IP routing table. EIGRP uses different packets and provides separate neighbors, topology and routing tables for each protocol in the Network layer.

    The IPX EIGRP module is responsible for exchanging routing information about IPX networks with other IPX routes.

    RTP and EIGRP Package Types

    The Trusted Transport Protocol is the protocol used by EIGRP to deliver and receive the same packets, which is designed to operate as a routing protocol that runs outside the network layer so that services such as UDP and TCP cannot be accessed.

    Even if your name has a reliable word, even if it is possible to obtain a delivery through an unreliable ETPRP, you can identify these packages because a reliable RTP requires a confirmation of receipt that requires nothing.

    RTP can send packets with UNICAST or MULTICAST, the latter uses a reserved address: 224.0.0.10

    Routers with EIGRP can discover their neighbors through a package called “GREETING”, in most networks “greeting” packets are sent every 5 seconds and help keep the neighbors and their routes visible When the greeting is answered.

    The wait time tells the router the maximum time it will wait before receiving the next “greet” before declaring its neighbor “inaccessible”.

    As a rule, the waiting time is 3 times the salutation interval.

    Wait time before reporting a router = “dead”

    (It takes the router to send an e-mail) (3)

    When the timeout expires, the route is declared inactive and a new route is searched using queries.

    Limited updates

    EIGRP reserves some reserves as it does not send periodic updates on update packages, ONLY IN THE METRIC OF ROAD CHANGES.

    It is worth noting that these updates are PARTIAL because when this happens, the entire contents of a table are not sent, only information about route changes is sent.

    EIGRP also takes care to limit this route change information to the affected routers. The partial update is automatically updated to “Limits”, so only routers that require this information.

    Sending ONLY the necessary routing information and ONLY to the routers in need minimizes the bandwidth required to send packets.

    Administrative Distance

    The administrative distance is the “degree of reliability ın of the route.

    EIGRP has 90 administrative distances for internal routes and 170 administrative distances for routes imported from an external source (including default routes)

    Compared to other protocols, the EIGRP has less administrative distance, in other words, IT IS MORE RELIABLE.

    Authentication

    It accepts security settings and can encrypt and verify your routing information.

    It is recommended that authentication is always performed on the transmitted routing information, ensuring that routers will only accept routing information from routers configured with the same password or authentication information.

    Protocols such as:

    · RIPv2
    · OSPF
    · IS-IS
    · BGP

    They also accept encryption in routing information.

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    Source: https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html