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الموضوع: CCNA Quick Notes

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    عضو برونزي الصورة الرمزية 7amasa7
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    CCNA Quick Notes



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    وجدت هذه ال quick notes فى احد ال bloges الخاصه بامتحان سيسكو ccna فحبيت انقلهلكم لانى حسيت انها قويه جدا ومفيده جداا واعتقد انها على طريقة اسئلة الانترفيو فيارب تفيدكم

    Quick notes LAN
    What is carrier sense multiple access collision detect (CSMA/CD)?
    CSMA/CD describes the Ethernet access method. In CSMA/CD, many stations can transmit on the same cable, and no station has priority over any other. Before a station transmits, it listens on the wire to make sure no other station is transmitting. If no other station is transmitting, the station transmits across the wire. CSMA/CD is all about devices taking turns using the wire.

    What are MAC addresses?
    For computers to identify each other on the data link layer, they need a MAC address (hardware address). All devices on a LAN must have a unique MAC address. A MAC address is a 48-bit (six octet) address burned into a network interface card. The first three octets (24 bits) of the MAC address indicate the vendor that manufactured the card. This is called the Organization Unique Identifier (OUI). The last three octets of the MAC address are the unique host address. An example of a MAC address is 00-80-C6-E7-9C-EF.

    What are the three types of LAN traffic?
    The three types of LAN traffic are:
    Unicasts
    Broadcasts
    Multicasts

    What are unicast frames?
    Unicast frames are the most common type of LAN traffic. A unicast frame is a frame intended for only one host. In unicast frames, the only station that processes the frame is the station that has its own MAC address in the destination portion of the packet.

    What are broadcast frames?
    Broadcast frames are frames intended for everyone. Stations view broadcast frames as public service announcements. All stations receive and process broadcast frames. In large networks, broadcasts can bring the network to a crawl, because every computer must process them.

    What is the destination address of broadcast frames?
    The destination address of broadcast frames (Layer 2 broadcast addresses) is FF-FF-FF-FF-FF-FF, or all 1s in binary.

    What are multicast frames?
    Multicast frames address a group of devices that have a common interest. These frames allow the source to send only one copy of the frame on the network even though it is intended for several stations. Only stations that have a card that is configured to receive multicast frames process them. All other stations discard multicast frames.


    What devices can you use to segment a LAN at Layer 1, Layer 2, and Layer 3?
    Three devices you can use to segment a LAN are:
    Hubs/repeaters (Layer 1)
    Bridges/switches (Layer 2) - physical addresses
    Routers (Layer 3) - logical addresses

    What happens when you segment the network with hubs/repeaters?
    Because hubs and repeaters operate at the physical layer of the OSI model, segmenting a network with these devices appears as an extension to the physical cable. Hubs and repeaters are transparent to devices. They are unintelligent devices. All devices that connect to a hub/repeater share the same bandwidth. Hubs/repeaters create a single broadcast and collision domain.

    What is the advantage of segmenting a network with bridges/switches?
    Bridges/switches operate at Layer 2 of the OSI model and filter by MAC address. Each port on a bridge/switch provides full-dedicated bandwidth and creates a single collision domain. Because bridges/switches operate at Layer 2 of the OSI model, they cannot filter broadcasts, and they create a single broadcast domain. For the CCNA test, remember that switches create more collision domains and fewer collisions.

    What is the difference between bridges and switches?
    Bridges and switches function the same way; the only difference is in how they are implemented. Bridges are implemented by software and usually have a couple of network ports. Switches are implemented in hardware by ASIC chips and have many ports.

    What are the advantages and disadvantages of segmenting the LAN with routers?
    An advantage of segmenting the LAN with routers is that each interface on a router creates a single broadcast and collision domain. Routers operate at Layer 3 of the OSI model and do not propagate broadcasts. Some disadvantages are that routers are not transparent and are implemented in software, thus introducing latency in the network.


    What is the Maximum Transmission Unit (MTU) for an Ethernet frame?
    1500 bytes is the MTU for an Ethernet frame. You will notice that some publications state that the MTU for Ethernet is 1518 bytes. This is correct also. But what is the true answer? The MTU for Ethernet, including the header, source and destination address, data, and CRC is 1518 bytes. The MTU for the data portion of the frame is 1500 bytes.

    What three major functions do Layer 2 switches provide?
    The three major functions that Layer 2 switches provide are
    Address learning
    Packet forwarding/filtering
    Loop avoidance by spanning tree

    What are some advantages of switches?
    Some advantages of switches are as follows:
    They increase available network bandwidth.
    They reduce the number of users per segment.
    They provide dedicated bandwidth to each segment.
    Transparent bridging (switching) provides five bridging functions to determine what to do when it receives a frame.

    What are these five processes?
    The five processes are:
    Learning
    Flooding
    Filtering
    Forwarding
    Aging

    In transparent bridging, what is the learning process?
    The first process a bridge goes through when it is powered on is the learning process. The MAC address table on the bridge contains no entries, and the bridge goes through the learning process to record all workstations on every interface. In the learning process, the bridge records the source MAC address and source port number in the MAC address table every time it sees a frame.

    In transparent bridging, what is the flooding process?
    When a bridge is first turned on, it has no MAC address in its table. When a switch receives a unicast frame, it knows the source address and port from which the unicast frame came, but no entry exists in its table for the destination address. This is called an unknown unicast frame. When a switch receives an unknown unicast frame, it sends the frame out all forwarding interfaces on the bridge except the interface that received the frame. This process is the flooding process.

    In transparent bridging, what is the filtering process?
    The filtering process occurs when the source and destination addresses reside on the same interface on the bridge. Because the bridge does not need to forward a frame in which the destination and source addresses reside on the same interface, it filters the frame and discards it.

    In transparent bridging, what is the forwarding process?
    The forwarding process occurs when a switch receives a unicast frame and has an entry of the destination address in its MAC table. The switch then forwards the frame to the interface where that destination address resides.

    In transparent bridging, what occurs during the aging process?
    Every time a bridge learns a source address, it time-stamps the entry. When the bridge sees a frame from this source, it updates the time stamp. If the bridge does not hear from the source for a specific amount of time (called the aging timer), the bridge deletes the entry from its MAC address table. This process is the aging process.

    What is the default aging time in transparent bridges?
    The default aging timer is 5 minutes.

    What is the Spanning-Tree Protocol (STP)?
    STP is a loop-prevention bridge-to-bridge protocol. Its main purpose is to dynamically maintain a loop-free network. It does this by sending out Bridge Protocol Data Units (BPDUs), discovering any loops in the topology, and blocking one or more redundant links.

    How does STP maintain a loop-free network?
    STP maintains a loop-free network by
    Electing a root bridge
    Electing a root port on each nonroot bridge
    Electing designated ports
    Putting in the blocking state any port that is not a root port or designated port

    What two key concepts does STP calculation use to create a loop-free topology?
    The two key concepts that STP uses to calculate a loop-free topology are
    Bridge ID (BID)
    Path cost

    In spanning tree, what is a Bridge ID (BID)?
    A BID is an 8-byte field that is composed of the bridge's 6-byte MAC address and a 2-byte bridge priority.

    What is the default bridge priority in a Bridge ID for all Cisco switches?
    32,768

    In spanning tree, what is path cost?
    Path cost is a calculation to determine the link's bandwidth. It is a value assigned to each port that is based on the port's speed.

    What is the spanning tree path cost for each of the following?
    10 Mbps
    100 Mbps
    1 Gbps
    The path costs are as follows:
    10 Mbps - 100
    100 Mbps - 19
    1 Gbps - 4

    When calculating a loop-free environment, what four-step decision sequence does spanning tree use to determine what will be the root bridge and which ports will forward or block?
    The four-step decision sequence that spanning tree uses to determine the root bridge and which port will forward is as follows:
    Step 1. The lowest root BID
    Step 2. The lowest path cost to the root bridge
    Step 3. The lowest sender BID
    Step 4. The lowest port ID

    How do bridges pass spanning tree information between themselves?
    Bridges pass STP information using special frame called Bridge Protocol Data Units (BPDUs).

    How often do bridges send BPDUs out active ports?
    The default time that bridges send BPDUs out active ports is 2 seconds.
    Note: All ports on a switch listen for BPDUs in case there is a topology change.

    In STP, how is a root bridge elected?
    In STP, the bridge with the lowest BID is elected the root bridge. All ports on the root bridge are placed in the forwarding state and are called designated ports.
    Note: The BID is a 6-byte field that is composed of a default priority (32,76 and a MAC address. Because all Cisco switches use the default priority, the switch with the lowest MAC address is elected the root bridge. As a rule of thumb, lower will always win in spanning tree.

    After bridges elect the root bridge, what do they do next?
    After electing the root bridge, switches elect root ports. A root port is the port on nonroot bridges that is closest to the root bridge. Every nonroot bridge must select one root port.

    How do nonroot bridges decide which port they will elect as a root port?
    Nonroot bridges use root path cost to determine which port will be the root port. Root path cost is the cumulative cost of all links to the root bridge. The port with the lowest root path cost is elected the bridge's root port and is placed in the forwarding state.

    What is the difference between path cost and root path cost?
    Path cost is the value assigned to each port. It is added to BPDUs received on that port to calculate the root path cost. Root path cost is defined as the cumulative cost to the root bridge. In a BPDU, this is the value transmitted in the cost field. In a bridge, this value is calculated by adding the receiving port's path cost to the value contained in the BPDU.

    If a nonroot bridge has two redundant ports with the same root path cost, how does the bridge choose which port will be the root port?
    If a nonroot bridge has redundant ports with the same root path cost, the deciding factor is the port with the lowest port ID (port number).

    After the root bridge and root ports are selected, the last step in spanning tree is to elect designated ports. How do bridges elect designated ports?
    In spanning tree, each segment in a bridged network has one designated port. This port is a single port that both sends and receives traffic to and from that segment and the root bridge. All other ports are placed in a blocking state. This ensures that only one port on any segment can send and receive traffic to and from the root bridge, ensuring a loop-free topology. The bridge containing the designated port for a segment is called the designated bridge for that segment. Designated ports are chosen based on cumulative root path cost to the root bridge.
    Note: Every active port on the root bridge becomes a designated port.

    If a bridge is faced with a tie in electing designated ports, how does it decide which port will be the designated port?
    In the event of a tie, STP uses the four-step decision process discussed in Question 30. It first looks for the BPDU with the lowest BID; this is always the root bridge. If the switch is not the root bridge, it moves to the next step: the BPDU with the lowest path cost to the root bridge. If both paths are equal, STP looks for the BPDU with the lowest sender BID. If these are equal, STP uses the link with the lowest port ID as the final tiebreaker.

    What are the four spanning tree port states?
    The four spanning tree port states are
    Blocking
    Listening
    Learning
    Forwarding
    Remember that root and designated ports forward traffic and that nondesignated ports block traffic but still listen for BPDUs.
    Important note: There is another port state - Disabled - (No frames forwarded, no BPDUs heard). If it shows up in the answer options - select it along with the others.

    What is the STP blocking state?
    When a switch starts, all ports are in the blocking state. This is to prevent any loops in the network. If there is a better path to the root bridge, the port remains in the blocked state. Ports in the blocked state cannot send or receive traffic, but they can receive BPDUs.

    What is the STP listening state?
    Ports transition from a blocked state to a listening state. In this state, no user data is passed. The port only listens for BPDUs. After listening for 15 seconds (if the bridge does not find a better path), the port moves to the next state, the learning state.

    What is the STP learning state?
    In the STP learning state, no user data is being passed. The port quietly builds its bridging table. The default time in the learning state is 15 seconds.

    What is the STP forwarding state?
    After the default time in the learning state is up, the port moves to the forwarding state. In the forwarding state, the port sends and receives data.

    What is STP forward delay?
    The forward delay is the time it takes for a port to move from the listening state to the learning state or from the learning state to the forwarding state. The default time is 30 seconds.

    What is the hello time in STP timers?
    The hello time is the time interval between the sending of BPDUs. The default time is 2 seconds.

    What is the Max Age timer?
    The Max Age timer is how long a bridge stores a BPDU before discarding it. The default time is 20 seconds (ten missed hello intervals).

    What is the default time a port takes to transition from the blocking state to the forwarding state?
    The default time a port takes to transition from the blocking state to the forwarding state is 50 seconds: 20 seconds for Max Age, 15 seconds for listening, and 15 seconds for learning.

    What does STP do when it detects a topology change in the network due to a bridge or link failure?
    If spanning tree detects a change in the network due to a bridge or link failure, at least one bridge interface changes from the blocking state to the forwarding state, or vice versa
    وان شاء الله فى حاجات تانيه كتير
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  2. #2
    عضو برونزي الصورة الرمزية 7amasa7
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    رد: CCNA Quick Notes


    Quick notes WAN


    The three WAN connection types available are leased lines, circuit-switched, and packet-switched. Define the differences between each connection type.
    Leased lines are dedicated point-to-point lines that provide a single preestablished WAN communication path from the customer's network to the remote network. Leased lines are usually employed over synchronous connections. They are generally expensive and are always up. Circuit-switched connections are dedicated for only the duration of the call. The telephone system and ISDN are examples of circuit-switched networks. Packet-switched connections use virtual circuits (VCs) to provide end-to-end connectivity. Packet-switched connections are similar to leased lines, except that the line is shared by other customers. A packet knows how to reach its destination by programming of switches. Frame Relay is an example of a packet-switched connection.

    Define customer premises equipment (CPE), and give an example.
    CPE is equipment that is located on the customer's (or subscriber's) premises. It is equipment owned by the customer or equipment leased by the service provider to the customer. An example is your router.

    What is the demarcation point (demarc)?
    The demarc is the point where the CPE ends and the local loop begins. It is the last responsibility of the service provider and is usually an RJ-45 jack located close to the CPE. Think of the demarc as the boundary between the customer's wiring and the service provider's wiring.

    What is the local loop?
    The local loop is the physical cable that extends from the demarc to the central office.

    Describe the central office (CO).
    The CO is the telco switching facility that connects the customer to the provider's switching network. The CO is sometimes referred to as a point of presence. It is the point where the local loop gains access to the service provider's access lines.

    What is the toll network?
    All the telco switches, COs, and trunk lines inside the WAN provider's network are the toll network.

    What are synchronous links?
    Synchronous links have identical frequencies and contain individual characters encapsulated in control bits, called start/stop bits, that designate the beginning and end of each character. Synchronous links try to use the same speed as the other end of a serial link.

    What are asynchronous links?
    Asynchronous links send digital signals without timing. Asynchronous links agree on the same speed, but there is no check or adjustment of the rates if they are slightly different. Only 1 byte per transfer is sent.

    List some typical Layer 2 encapsulation methods for WAN links.
    . High-Level Data Link Control (HDLC)
    · Point-to-Point Protocol (PPP)
    · Serial Line Internet Protocol (SLIP)
    · X.25/Link Access Procedure, Balanced (LAPB)
    · Frame Relay· Asynchronous Transfer Mode (ATM)

    Describe HDLC.
    HDLC was derived from Synchronous Data Link Control (SDLC). It is the default encapsulation type on point-to-point dedicated links and circuit-switched connections between Cisco routers. It is an ISO-standard bit-oriented data-link protocol that encapsulates data on synchronous links. HDLC is a connection-oriented protocol that has very little overhead. HDLC lacks a protocol field and therefore cannot encapsulate multiple network layer protocols across the same link. Because of this, each vendor has its own method of identifying the network-layer protocol. Cisco offers a propriety version of HDLC that uses a type field that acts as a protocol field, making it possible for multiple network-layer protocols to share the same link.

    By default, Cisco uses HDLC as its default encapsulation method across synchronous lines (point-to-point links). If a serial line uses a different encapsulation protocol, how do you change it back to HDLC?
    To change a serial line back to HDLC, use the following interface command on the serial interface you want to change: Router(config-if)#encapsulation hdlc

    What is the Point-to-Point Protocol (PPP)?
    PPP is an industry-standard protocol that provides router-to-router or router-to-host connections over synchronous and asynchronous links. It can be used to connect to other vendors' equipment. It works with several network-layer protocols, such as IP and IPX. PPP provides authentication through PAP or CHAP.

    Describe X.25/LAPB.
    X.25/LAPB is an ITU-T standard that has a tremendous amount of overhead because of its strict timeout and windowing techniques. LAPB is the connection-oriented protocol used with X.25. It uses the ABM (Asynchronous Balance Mode) transfer mode. X.25/LAPB was used in the 1980s when WAN links were not as error-free as they are today. X.25 is a predecessor of Frame Relay. X.25 supports both switched and permanent virtual circuits.

    What is Frame Relay?
    An industry standard, Frame Relay is a switched data link layer protocol that uses virtual circuits to identify the traffic that belongs to certain routers. It provides dynamic bandwidth allocation and congestion control.

    How do you view the encapsulation type on a serial interface?
    To view the encapsulation type on a serial interface, use the show interface serial interface-number command:
    RouterB#show interface serial 0
    Serial0 is up, line protocol is up Hardware is HD64570
    Internet address is 192.168.1.1/24
    MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
    Encapsulation HDLC, loopback not set, keepalive set (10 sec)
    Last input 00:00:00, output 00:00:03, output hang never
    Last clearing of "show interface" counters never
    Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/1000/64/0 (size/max total/threshold/drops)
    Conversations 0/1/256 (active/max active/max total)
    Reserved Conversations 0/0 (allocated/max allocated)
    5 minute input rate 0 bits/sec, 0 packets/sec
    5 minute output rate 0 bits/sec, 0 packets/sec
    9 packets input, 1730 bytes, 0 no buffer
    Received 8 broadcasts, 0 runts, 0 giants, 0 throttles
    0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
    7 packets output, 1584 bytes, 0 underruns
    0 output errors, 0 collisions, 2 interface resets
    0 output buffer failures, 0 output buffers swapped out
    5 carrier transitions
    DCD=up DSR=up DTR=up RTS=up CTS=UP
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  3. #3
    عضو برونزي الصورة الرمزية 7amasa7
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    رد: CCNA Quick Notes

    Quick notes internetworking
    [SIZE="1"][SIZE="3"]
    What are the three layers of the Cisco Hierarchical Model?
    The three layers of the Cisco Hierarchical Model are:1
    The access layer
    The distribution layer
    The core layer


    In the Cisco Hierarchical Model, what is the function of the access layer?
    Sometimes referred to as the desktop layer, the access layer is the point at which users connect to the network through low-end switches. Some functions of the access layer include:
    Connectivity into the distribution layer
    Shared Bandwidth
    MAC Address filtering (switching)
    Segmentation


    What is the function of the distribution layer in the Cisco Hierarchical Model?
    The distribution layer is also known as the workgroup layer. It is the demarcation point between the access and core layers of the network. Its primary function is to provide routing, filtering, and WAN access. The distribution layer determines how packets access the core, so it is the layer at which to implement policy-based connectivity. Some functions include the following:
    Collection point for access layer devices
    Broadcast and multicast domain segmentation
    Security and filtering services such as firewalls and access lists
    Providing translation between different media types
    Inter-VLAN routing


    What is the role of the core layer in the Cisco Hierarchical Model?
    The core layer is the backbone of the network. Its main function is to switch traffic as fast as possible. Therefore, it should not perform any filtering to slow down traffic.
    The ISO's OSI Reference Model contains seven layers. What are they? Include the layer number and name of each layer in your answer.
    The seven layers of the OSI model are as follows:
    Layer 7 - Application layer

    Layer 6 - Presentation layer

    Layer 5 - Session layer

    Layer 4 - Transport layer

    Layer 3 - Network layer

    Layer 2 - Data link layer

    Layer 1 - Physical layer


    What are some reasons that the industry uses a layered model?
    Here are some reasons why the industry uses a layered model:
    It encourages industry standardization by defining what functions occur at each level.
    It allows vendors to modify or improve components at only one layer versus rewriting the whole protocol stack.
    It helps interoperability by defining standards for the operations at each level.
    It helps with troubleshooting.


    What does the application layer (Layer 7) of the OSI model do, and what are some examples of this layer?
    The application layer is the layer that is closest to the user. This means that this layer interacts directly with the software application. The application layer's main function is to identify and establish communication partners, determine resource availability, and synchronize communication. Some examples include the following:
    TCP/IP applications such as Telnet, File Transfer Protocol (FTP), Simple Mail Transfer Protocol (SMTP), WWW, and HTTP.
    OSI applications such as Virtual Terminal Protocol, File
    Transfer, Access, and Management (FTAM), and Common Management Information Protocol (CMIP).


    In the OSI model, what are the responsibilities of the presentation layer (Layer 6)? Give some examples of this layer.
    Also known as the translator, the presentation layer provides coding and conversion functions to application layer data. This guarantees that the application layer on another system can read data transferred from the application layer of a different system. Some examples of the presentation layer are:
    Compression, decompression, and encryption
    JPEG, TIFF, GIFF, PICT, QuickTime, MPEG, and ASCII


    What are the functions of the session layer (Layer 5)? Give some examples.
    The session layer is responsible for creating, managing, and ending communication sessions between presentation layer entities. These sessions consist of service requests and responses that develop between applications located on different network devices. Some examples include SQL, RPC, NFS, X Window System, ZIP, NetBIOS names, and AppleTalk ASP.


    What is the transport layer (Layer 4) responsible for? Give some examples of transport layer implementations.
    The transport layer segments and reassembles data from upper-layer applications into data streams. It provides reliable data transmission to upper layers. End-to-end communications, flow control, multiplexing, error detection and correction, and virtual circuit management are typical transport layer functions. Some examples include TCP, UDP*, and SPX.
    Note: watch out for end-to-end on communications on the exam! Transport layer.


    * Error correction does not apply to UDP - connection-less - unreliable.....


    What is flow control, and what are the three methods of implementing it?
    Flow control is the method of controlling the rate at which a computer sends data, thus preventing network congestion. The three methods of implementing flow control are
    Buffering
    Congestion avoidance
    Windowing
    Almost certain to be on the exam.


    Describe the function of the network layer (Layer 3), and give some examples of network layer implementations.
    The network layer provides internetwork routing and logical network addresses. It defines how to transport traffic between devices that are not locally attached. The network layer also supports connection-oriented and connectionless service from higher-layer protocols. Routers operate at the network layer. IP, IPX, AppleTalk, and DDP are examples of network layer implementations.


    Are network layer addresses physical or logical?
    Network layer addresses are logical addresses specific to the network layer protocol being run on the network. Each network layer protocol has a different addressing scheme. They are usually hierarchical and define networks first and then host or devices on that network. An example of a network address is an IP address, which is a 32-bit address often expressed in decimal format. 192.168.0.1 is an example of an IP address in decimal format.


    How do routers function at the network layer of the OSI model?
    Routers learn, record, and maintain awareness of different networks. They decide the best path to these networks and maintain this information in a routing table. The routing table includes the following:
    Network addresses, which are protocol-specific. If you are running more than one protocol, you have a network address for each protocol.
    The interface the router uses to route a packet to a different network.
    A metric, which is the distance to a remote network or the weight of the bandwidth, load, delay, and reliability of the path to the remote network.
    Routers create broadcast domains. One interface on a router creates a single broadcast domain and collision domain. However, an interface on a switch creates only a single collision domain.


    In addition to learning the remote network and providing a path to the network, what other functions do routers carry out?
    Routers perform these tasks:
    Routers, by default, do not forward broadcasts or multicasts.
    Routers can perform bridging and routing functions.
    If a router has multiple paths to a destination, it can determine the best path to the destination.
    Routers forward traffic based on Layer 3 destination addresses.
    Routers can connect Virtual LANs (VLANs).
    Routers can provide quality of service for specified types of network traffic.


    What is the responsibility of the data link layer (Layer 2)?
    The data link layer provides functional and procedural means for connectionless mode among network entities, and for connection mode entities it provides the establishment, maintenance, and release of data link connections among network entities and for the transfer of data link service data units. The data link layer translates messages from the network layer into bits for the physical layer, and it enables the network layer to control the interconnection of data circuits within the physical layer. Its specifications define different network and protocol characteristics, including physical addressing, error notification, network topology, and sequencing of frames. Data link protocols provide the delivery across individual links and are concerned with the different media types, such as 802.2 and 802.3. The data link layer is responsible for putting 1s and 0s into a logical group. These 1s and 0s are then put on the physical wire. Some examples of data link layer implementations are IEEE 802.2/802.3, IEEE 802.5/802.2, packet trailer (for Ethernet, the FCS or CRC), FFDI, HDLC, and Frame Relay.


    The IEEE defines what two sublayers of the data link layer?
    The two sublayers of the data link layer are
    The Logical Link Control (LLC) sublayer
    The Media Access Control (MAC) sublayer
    These two sublayers provide physical media independence.


    For what is the LLC sublayer responsible?
    The Logical Link Control (802.2) sublayer is responsible for identifying different network layer protocols and then encapsulating them to be transferred across the network. An LLC header tells the data link layer what to do with a packet after it is received.


    What functions does the Media Access Control (MAC) sublayer provide?
    The MAC sublayer specifies how data is placed and transported over the physical wire. The LLC layer communicates with the network layer, but the MAC layer communicates downward directly to the physical layer. Physical addressing (MAC addresses), network topologies, error notification, and delivery of frames are defined at this sublayer.


    What are some network devices that operate at the data link layer?
    Bridges and switches are network devices that operate at the data link layer. Both devices filter traffic by MAC addresses.


    What is the function of the OSI model's physical layer (Layer 1)? Give some examples of physical layer implementations.
    The physical layer defines the physical medium. It defines the media type, the connector type, and the signaling type (baseband versus broadband). This includes voltage levels, physical data rates, and maximum cable lengths. The physical layer is responsible for converting frames into electronic bits of data, which are then sent or received across the physical medium. Twisted pair, coaxial cable, and fiber-optic cable operate at this level. Other implementations at this layer are repeaters/hubs, RJ-45.


    The Ethernet and IEEE 802.3 standards define what three physical wiring standards that operate at 10 Mbps?
    These physical wiring standards operate at 10 Mbps:
    10Base2
    10Base5
    10BaseT


    What are collision domains?
    In Ethernet segments, devices connect to the same physical medium. Because of this, all devices receive all signals sent across the wire. If two devices send a packet at the same time, a collision occurs. In the event of a collision, the two devices run a backoff algorithm and resend the packet. The devices retransmit up to 15 times. The first station to detect a collision issues a jam signal. When a jam signal is sent from a workstation, it affects all of the machines on the segment, not just the two that collided; when the jam signal is on the wire, no workstations can transmit data. The more collisions that occur in a network, the slower it will be, because the devices will have to resend the packet. A collision domain defines a group of devices connected to the same physical medium.


    What are broadcast domains?
    A broadcast domain defines a group of devices that receive each others' broadcast messages. As with collisions, the more broadcasts that occur on the network, the slower your network will be. This is because every device that receives a broadcast must process it to see if the broadcast is intended for it.


    What devices are used to break up collision and broadcast domains?
    Switches and bridges are used to break up collision domains. They create more collision domains and fewer collisions. Routers are used to break up broadcast domains. They create more broadcast domains and smaller broadcast areas.


    How do the different layers of the OSI model communicate with each other?
    Each layer of the OSI model can communicate only with the layer above it, below it, and parallel to it (a peer layer). For example, the presentation layer can communicate with only the application layer, session layer, and presentation layer on the machine it is communicating with. These layers communicate with each other using protocol data units (PDUs). These PDUs control information that is added to the user data at each layer of the model. This information resides in fields called headers (the front of the data field) and trailers (the end of the data field).
    What is data encapsulation?
    A PDU can include different information as it goes up or down the OSI model. It is given a different name according to the information it is carrying (the layer it is at). When the transport layer receives upper layer data, it adds a TCP header to the data; this is called a segment. The segment is then passed to the network layer, and an IP header is added; thus, the data becomes a packet. The packet is passed to the data link layer, thus becoming a frame. This frame is then converted into bits and is passed across the network medium. This is data encapsulation. For the CCNA test, you should know the following:
    Application layer -- Data
    Transport layer -- Segment
    Network layer -- Packet
    Data link layer -- Frame
    There is also the Physical Layer -- Bits


    What is the difference between a routing protocol and a routed protocol?
    Routing protocols determine how to route traffic to the best location of a routed protocol. Examples of routing protocols are RIP, EIGRP, OSFP, and BGP. Examples of routed protocols are IP and IPX.


    What 3 devices are used to segment a LAN?
    Router
    Switch
    Bridge
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    جزاك الله خيرا عنا ربنا يجعله لك فى ميزان حسناتك
    بسم الله الرحمن الرحيم

    أَمَّنْ يُجِيبُ الْمُضْطَرَّ إِذَا دَعَاهُ وَيَكْشِفُ السُّوءَ وَيَجْعَلُكُمْ خُلَفَاءَ الْأَرْضِ أَءِلَهٌ مَعَ اللَّهِ قَلِيلًا مَا تَذَكَّرُونَ
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    رائع جداً
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    الملفات المرفقة الملفات المرفقة
    إذا ضاقت بك الدنيا فلا تقل , يا رب عندي هم
    كبير ..... ولاكن قل يــا هم لــي رب كبيـــــر

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