CCNA Study Notes (i) Network Interconnection Foundation

1. Network Segment (segmentation)

In order to cope with the increase of the network caused by slow user response and traffic congestion, the large network is divided into a number of small network behavior. You can use devices such as routers, switches, and bridges.

2. Common reasons that cause LAN congestion:

① too many hosts in the same broadcast domain or conflict domain;

② broadcast storm;

③ Multicast data flow too much;

④ bandwidth is too low;

⑤ extends the network with hubs.

3, the hub can not segment the network, but only to connect the network segment. Suitable for home networking and troubleshooting. (Signal amplifier)

4. Routers are used to connect multiple networks and route data packets between networks.

5, by default, the router splits the broadcast domain and also splits the conflict domain.

6. Broadcast domains (broadcast domain)

Refers to a collection of all the devices in the same network segment that are listening for all broadcasts sent in that network segment.

7. The router uses a serial interface to establish the WAN connection, which is the v.35 physical interface in the Cisco router.

8. When a host or server in a network sends a webcast, all devices in the network must read and process the broadcast, unless the router is used in the network.

9, the advantages of using routers in the network:

① By default, routers do not forward broadcasts

② routers can filter the network based on the third layer (network layer) information (such as IP address)

10, the function of the router:

① packet switching;

② packet filtering;

③ communication between networks;

④ Path Selection

11, the router is actually a third layer switch, using the logical address to provide packet switching functions, using the access list for packet filtering, using the routing table (internetwork map) to select the path and forward the packet to the remote network.

12, the switch is not used to build the internetwork, by default, the broadcast domain is not segmented, and to improve the function of the LAN, to provide higher bandwidth to LAN users.

13. The switch does not want the router to forward packets to other networks, but only to exchange frames between the ports in the switched network.

14. By default, the switch splits the conflict domain.

15. Conflict zone (collision domain)

Ethernet terminology refers to the fact that when a device sends a packet over a network, all other devices in the current network segment must be aware of this. If two devices attempt to transmit data at the same time, it will cause a conflict, and the two devices must retransmit the data separately, so that the efficiency is not high.

16. All hosts connected to a hub belong to the same conflict domain and broadcast domain. There are often conflicting phenomena.

17, each port of the switch is a separate conflict domain. But only one broadcast domain is created.

18. The basic functions of the bridge and the switch are the same, which divides the LAN into multiple conflict domains. Cisco still calls the LAN switch a multi-port bridge. (Smarter than traditional bridges)

19, the advantages of Network Bridge:

① reduce conflicts in the broadcast domain;

② increase the conflict domain in the network;

③ provides users with higher bandwidth

20. The use of hubs may make Ethernet more congested.

21. Although bridges/switches are used to segment networks, they cannot isolate broadcast domains and multicast groupings.

22, today's common network is composed of Exchange-type network. A network is established with the LAN switch as the core, and the router is connected to a logical network.

23. OSI Reference Model (Open Systems interconnection)

Divided into seven layers, 3+4 two groups, on the three layer specifies how applications in the terminal communicate with each other and how to communicate with the user; the next three layers specify how to perform end-to-end data transfer.

24, the application layer is the interface between the actual application program.

Many applications do not exist in the application layer, but interact with the application-layer protocol. For example, ie, when a user accesses the network through IE, IE will attempt to access the application layer and interact with the application layer protocol.

25. The presentation layer provides data to the application layer and is responsible for transforming the data and formatting the code. Essentially, the layer is a converter that provides encoding and conversion capabilities.

26. The session layer is responsible for establishing, managing, and terminating sessions between the presentation layer entities, as well as controlling the conversations between the devices or nodes.

Three different modes of communication are available: simplex, half-duplex, full duplex.

The basic function is to separate data from different applications.

27. The transport layer fragments the data from the upper application and reorganizes it into the data stream, establishes the logical connection between the sending host and the target host, and carries on the end-to-end transmission.

28. The Transport layer is responsible for providing the following mechanisms:

Multiplexing, establishing sessions, and dismantling virtual circuits for upper-level applications.

29. The Transport layer also provides a transparent data connection to hide information that varies from the network to the top.

30, the transport layer can be non-connected or connection-oriented, we pay more attention to the connection-oriented part.

31. Flow control: Designed to provide a mechanism for the receiver to control the amount of data sent by the sender.

Reliable data transfer can achieve the following objectives:

① after receiving the data section, confirm to the sending party;

② retransmission of all data segments that have not been confirmed;

③ data segments arrive at their destination, they are arranged in the correct order;

④ ensures that data traffic does not exceed processing power to avoid congestion, overloading, and data loss.

32. Connection-oriented communication--three-time handshake

① sends the data segment of the "Connection contract" to send the direction target for the request synchronization (SYN);

② the target responds the request to the sender and determines the connection parameters between the hosts, and the colleague requests the synchronization of the receiver's order to establish a two-way connection; (Syn/ack)

The ③ sender notifies the target host that the connection contract has been accepted and the connection has been established.

33, if the service has the following characteristics, it is connection-oriented:

① Establish virtual circuit (such as three-time handshake);

② using sorting techniques;

③ use confirmation;

④ uses flow control.

34, flow control methods include buffering, window technology and congestion avoidance.

35, Window Technology:

The number of data segments that can be sent is called a window in order to increase the transmission efficiency of the data segment that can be transmitted during the time the sender sends the data segment to the receiving acknowledgement.

The window is used to control the number of unacknowledged data segments.

36. If you do not receive all the bytes that should be acknowledged, the receiver should narrow the window to improve the communication session.

37, the sender of the data segment after the launch timer and wait for confirmation, if the timer has not been received after the acknowledgement of the receiver, the data segment is re-transmitted.

CCNA Study Notes (i) Network Interconnection Foundation