Computer network topics (not regularly updated)

1.

Network:

will be distributed indifferent LocationsComputers, terminals and their ancillary equipment, which have the ability to independentlycommunication equipment and communication line connectionand configure the network software to achieve the computingMachine resource SharingThe system.

2.

What is a domain name, IP address, and MAC address ? What is the relationship between them?

IP Address: An IP address can also be called an Internet address to identify a logical address that is located on each computer on the Internet . people assign a dedicated address, called an IP address, to each host in the Internet.

Domain name: a computer or group of computers on the Internet consisting of a dotted list of names used to identify the computer's electronic orientation (and sometimes geographic location) when data is transferred .

Physical Address (MAC:

Usually refers to the physical address of the network card , which is the MAC address. Each NIC chip has a unique MAC address, and the MAC address is a 12-bit 16-digit number, usually written in 2 groups.

MAC addresses cannot be permanently modified, but can be configured to replace the MAC address of the network card with a virtual address at the system level, and other hosts appear to be unable to differentiate between the virtual MAC address you are using or the physical MAC address.

Relationship : An IP address is a set of numbers that can be used in the property settings of the NIC to correspond to the NIC. That is , IP binds the physical address . domain name is to replace the bad memory of the IP address of the alias , the domain name is also bound to the IP

you can use the address.

3. What is a network protocol ? What is its role in the network?

Network protocol: A collection of rules, standards, or conventions established for data exchange in a computer network. Role: ① Ensure that computers in the network are connected , and ② ensure that the computers in the network Exchange messages correctly .

4. The Ethernet switch Works : The switch forwards the data through the MAC address . When two users connected to the switch send data at the same time, the switch first looks at the Switch table, which has a mapping of the record port and MAC address . The switch splits the conflict domain , and each port becomes a separate conflict domain . If there is a large amount of data sent per port, the port will first store the received data waiting to be sent to the register and send it back when it is sent.

5.DHCP : DHCP is the abbreviation for Dynamic Host Configuration protocol, which is one of the TCP/IP protocols, mainly used to assign dynamic IP addresses to network clients . These assigned IP addresses are pre-reserved address sets made up of multiple addresses by the DHCP server , and they are generally contiguous addresses.

6.TCP/IP protocol

TCP protocol : Mainly used to manage the quality of network communication, to ensure that there is no error in network transmission .

IP protocol: mainly used for network transmission to provide a communication address , to ensure accurate to find the computer to receive data.

7.VLAN : is a broadcast domain that can cross multiple physical regions logically , can be divided according to the division of Labor or Department of the

with the organization VLAN without regard to the actual location of the user, traffic between the different VLANs is isolated .

8.

There are several ways to forward information on the switch, and analyze its advantages and disadvantages.
① Direct Exchange

Advantage: Short delay time .
Cons: lack of error detection capability, data forwarding between different input/output rate ports is not supported.

② Store-and- forward switching
Pros: differential error detection capability and support for data forwarding between different input/output rate ports

Cons: Long switching delay time

③ Improved Direct switching

Advantage: For short data, the switching delay is close to the direct switching method.

Cons: For long data, the exchange delay will be reduced because it only makes error detection of the primary field in the front of the data .

9. How to divide VLANs:

1. According to the port to divide

　　VLANs use the port of the switch to partition VLAN members. The ports that are set are in the same broadcast domain. For example, the 1,2,3,4,5 port of a switch is defined as a virtual network AAA, and the 6,7,8 port of the same switch makes up the virtual network BBB. This allows for communication between the ports and allows for the upgrade of the shared network.

2. Dividing VLANs by MAC address
This method of partitioning VLANs is divided according to the MAC address of each host, that is, the host for each MAC address configures which group it belongs to. The biggest advantage of this method of partitioning the VLAN is that when the user's physical location is moved, that is, when switching from one switch to the other, the VLAN does not have to be reconfigured, so it can be considered that the MAC address partitioning method is based on the user's VLAN, the disadvantage of this method is the initialization of the  All users must be configured , if there are hundreds of or even thousands of users, the configuration is very tired. And this partitioning method also leads to a reduction in the efficiency of the switch execution, because there may be many VLAN members on each switch port, so the broadcast packet cannot be restricted. In addition, for users who use laptops , their network cards may be replaced frequently, so that VLANs must be constantly configured.

3. VLAN partitioning based on network layer
This method of partitioning VLANs is divided according to the Network layer Address or protocol type of each host (if multi-protocol is supported), although this partitioning method is based on the network address, such as the IP address, but it is not a route, and the network layer of the route has no relationship.

The advantage of this approach is that the user's physical location changes, does not need to reconfigure the VLAN, and can be divided according to the protocol type of VLAN, which is important for network managers, and this method does not require additional frame tags to identify the VLAN, which can reduce network traffic. 

 4. Partitioning VLANs based on IP   Multicast
IP Multicast is also actually a VLAN definition, that is, a multicast group is a VLAN, this partitioning method extends the VLAN to the WAN, so this method has greater flexibility, but also easy to extend through the router , Of course, this method is not suitable for the local area network, mainly efficiency is not high. 

10.

Data exchange technology: The way the continuous data unit is forwarded through the node. Exchange: The data is in the process of node entry and exit.
Packet: The transfer of data into a data unit in the network node in one out of the exchange process. This unit of data is usually called a packet. the application layer, the presentation layer and the session layer are defined as the transmission unit --the message, the transmission Layer--the message or datagram; Network layer--group; link layer--frame.
Three switching strategies:

1) circuit Exchange: is only used for communication between these two nodes. two will persist until one of them terminates communication . Excellent: fast. Applies to cases where the transmission delay is not allowed. Missing: Due to The network line is a dedicated , so other routes cannot be used. As with telephone calls, both parties must participate simultaneously.  

2) message exchange : only when a party has a message needs to be transmitted, the network temporarily set up a routing message, the message is complete, routing release . And the messages are stored by each passing node. Messages are sent to the destination and can be stored for access. Excellent: The route is non-exclusive , after the completion of a message transmission, can be immediately reused . The receiving party is not required to accept the message immediately. Missing: Usually the message takes longer to reach the destination. Because intermediate nodes must store the report , too long a message can cause problems. The tail of the message still follows the route that was originally set, regardless of whether the network condition has changed.   
3) packet switching: packet switching is essentially developed on the basis of "storage-forwarding". It also has the advantages of circuit switching and message exchange. The dynamic multiplexing technique of packet switching is used to transmit data divided into many small segments by a certain length--grouping. After each packet identification, a dynamic multiplexing technique is used on a physical line, and multiple data groupings are transferred. The data from the user's originator is temporarily present in the memory of the switch and then forwarded within the network. Arrive at the receiving end, then remove the packet header to reassemble the data fields in order to complete the message. Packet switching is more efficient than circuit switching, with less transmission delay and better interactivity than packet switching.
Packet Exchange Two ways : 11 datagram Mode: The network protocol treats each packet as a single message, routing it. 22 Virtual Circuit mode: Similar to circuit switching, the difference: The line is not dedicated! That is, different virtual circuits can share a common physical network line!

11.

What is the respective implementation principle of the switch and router? At which level are they implemented?

1) routers can be routed forward (connecting two different network segments and translating for two segments).

The switch is not capable of routing forwarding (connecting several different hosts of the same network segment , reducing intra-network conflicts, isolating conflict domains ). Increase the speed of the use of

hubs and switches have similar capabilities, but cannot isolate conflicting domains, so they are shared bandwidth .

2) Because of the above, so the router can not be forwarded to broadcast packets, can isolate the broadcast domain.

3) switch works at the data link layer, the router works on the network layer

12. Please explain the definition of IP protocol in detail, which layer is above? What is the main role? What about TCP and UDP?

IP Protocol (Internet Protocol), also known as Internet Protocol , is a datagram protocol that supports inter-network interconnection, which together with the TCP protocol ( Transmission Control Protocol) forms the core of the TCP/IP protocol family. It provides the perfect functionality for inter-network connectivity, including IP datagram-defined IP address formats within the Interconnect network range.

IP is a network layer protocol that works on top of the data link layer . the role of IP protocol is to provide a unified IP packet to the Transport Layer (TCP layer), the conversion of various types of Mac frames to a unified IP packet , and the physical address of the Mac frame to the whole network unified logical address (IP address). In this way, the differences between the Mac frames of these different physical networks no longer exist on the upper level. As a result of this transformation, the interconnection of different types of physical networks is realized.

both TCP and UDP are transport-layer protocols.

TCP (transmission Control Protocol, transmission Protocol) is a connection-oriented protocol that must be connected to each other before sending or receiving data.
UDP (User data Protocol, Subscriber Datagram Protocol) is the protocol that corresponds to TCP. It is a non-connection-oriented protocol that does not establish a connection with the other, but sends the packet directly past

Comparison of the OSI model and the TCP/IP model

Same point:

All have the same five layers, these five layers feature similar

Different points:

1) OSI has seven layers, TCP/IP has five layers (some say four layers)

2) OSI supports connectionless and connection-oriented communication at the network layer, and the transport layer has only connection- oriented communication

TCP/IP only has no connected communication at the network layer, and the Transport layer supports two modes of transmission

Computer network topics (not regularly updated)