Network hardware
It feels that if you leave the network, the development of the computer will be another scene, but there is a little bit of certain, it will not be colorful. It can be said that the computer shows endless vitality because the network has emerged.
For the network, in addition to mastering the basic OSI model, it is necessary to understand the basic network hardware. This is also the basis of learning the network, leaving hardware, then the network theory will be a paper empty talk.
(1) network cable
The network cable is very important as the basic device of the network connection. The connection between the different devices, the network cable used is not the same, such as the network cable used by the two computers and the network cable used to connect to the HUB connection.
1 From the medium, the network cable has the following three types:
Twisted pair: shield (STP) and non-mask (UTP, mainstream, suitable for RJ-45 interface, square), where the maximum allowable use length of CAT-5 is 100 meters, and the enhanced 100Base-TX network is not more than 220 meters.
Coaxial cable: Raw cable (suitable for AUI interface) and cable (suitable for BNC interface, round)
Fiber: Although it is not very popular now, it is definitely a future trend.
2 From the connection mode, the network cable is divided into two types:
The positive line, the straight line, 568b: two-end line sequence, from left to right, line sequence: white orange, orange, white green, blue, white blue, green, white brown, brown.
Applicable to: PC-HUB
Hub (ordinary port) -hub (cascading)
Hub (cascaded) -switch
Switch-router
Anti-line, ie intersection, 568A: One end is the line order of the positive line, the other end is from left to right: white green, green, white orange, blue, white blue, orange, white brown, brown.
Suitable for: PC-PC
Hub (ordinary mouth) - hub (ordinary mouth)
Hub (cascaded) -hub (cascaded)
Hub-switch
Switch-switch
Router-router
(2) NIC and modem
1 NIC and modem difference: NIC is a direct interface of a computer and a local area network communication medium. The BIT data signal is transmitted. The current mainstream technology is Ethernet technology; the modem is transmitted by using a public switched telephone network, transmitted Pulse type analog signals, the main role of modems is to perform digital / analog signals directly in computer and networks, one of the ways of computer access to WAN.
2 Netcom has the following types according to network technology, interface, bus:
Network technology: ATM network card, token ring network card, Ethernet network card (mainstream)
Interface type: AUI interface (thick cable), BNC interface (cable), RJ-45 interface (twisted pair, mainstream)
Bus Type: ISA, EISA, PCI (mainstream)
(3) hub
The essence of the hub is a multi-port repeater that works in the physical layer, does not have automatic addressing and capacity and exchange, to form a shared network. Since the network cable has a certain transmission distance limit, the signal during transmission generates attenuation, and the hub can perform the signal of the signal reproduction and forwarding and have a plurality of ports, so it is a selection of multiple computers. The hub performs signal forwarding mainly uses information broadcasting methods, and destination ports determine whether to accept information based on the destination address in the frame format. Each port of the hub transmits acceptance data in a CSMA / CD method, so the network terminal connected to the hub is in the same conflict domain.
(4) Bridge
The bridge works in the data link layer, connects two LANs, forwards frames, isolates the conflict domain, but does not isolate the broadcast domain. Since the bridge is forwarded on the data frame, only the same or similar network (data frames of the same or similar structure), such as the Ethernet, the Ethernet and the token ring between the TOKEN RING. Interconnection, for different types of networks (different data frame structures), such as between Ethernet and X.25, the bridge is powerless.
The bridge can be divided into the following:
1 transparent bridge
The transparent bridge has the characteristics of plug-and-play, in a mixed manner, and is achieved in reverse self-learning. The forwarding and filtration of the bridge is done through the bridge table. The bridge table is initially empty, and the entry is increased by self-learning, each entry has a certain aging time.
(1) If the source LAN is the same as the destination, the frame is discarded.
(2) If the source LAN and the destination LAN are different, the frame is forwarded.
(3) If the destination LAN is unknown, spread
2 spanning tree bridge
There may be multiple redundant paths in the LAN network segment. In this case, the frame may cycle and reproduce, block the network, and ultimately make the entire network crash, so use the generated tree bridge virtual disconnection. interface. The implementation method is that each bridge broadcasts its serial number (the serial number is set by the manufacturer and ensures the world's only), and the selected sequence number is the smallest bridge as the root. Next, construct the generated tree according to the shortest path to each bridge.
(5) switch
The switch is a high-performance multi-port bridge, working on the second floor.
1 three exchange technology
Port exchange
Frame exchange
Cell Exchange (ATM)
2 virtual network
The switch can divide the network into a virtual network to manage and limit the broadcast storm to a certain range.
(6) router
When a host in the IP subnet sends an IP packet to another host of the same IP subnet, it will send the IP packet to the network directly, and the other party can receive it. When it is given to different IPs on the Internet, it is to select a router that can reach the subnet, and give the IP packet to the router, and the router is responsible for sending the IP packet to the destination. If such a router is not found, the host gives an IP packet to a router called "default gateway". "Default Gateway" is a configuration parameter on each host, which is an IP address of a router port on the same network.
When the router forwards the IP packet, only the appropriate port is selected according to the network number portion of the IP group's IP address, and the IP packet is sent out. Like the host, the router also determines whether the port is connected is a destination subnet. If so, send the packet directly to the network through the port, otherwise, select the next router to transmit the packet. The router also has its default gateway to transmit IP packets that do not know where to send. In this way, the IP packet knows how to transmit the IP packet is given to the "default gateway" router, which will eventually send it to the destination, the IP group will eventually be delivered to the destination, the IP group will eventually be delivered to the destination The IP packet is discarded by the network. At present, TCP / IP networks are all interconnected through routers, and the Internet is the international network of thousands of IP subnets through routers. This network is called a router-based network, which forms "network network" with a router as a node. In "Internet", the router is not only responsible for the forwarding of IP packets, but also responsible for contact with other routers to determine the routing and maintenance routing table of "Internet Network".
Routing action includes two basic contents: diameter and forwarding. The finding diameter determines the optimal path to the destination, and is implemented by the routing algorithm. Some complicated are relatively complicated due to different routing protocols and routing algorithms. In order to determine the best path, the routing algorithm must start and maintain the routing table containing routing information, where routing information depends on the route selection algorithm used. The routing algorithm fills in the routing table in accordance with the routing table to tell the router according to the routing table. The relationship between the destination network and the next stop. Route interworking information is routing updates, updating the maintenance routing table correctly reflects the topology change of the network, and determines the best path by the router according to the measurement. This is the Routing Protocol, such as Routing Information Protocol (RIP), Open Shortest Path Priority Protocol (OSPF), and Boundary Gateway Protocol (BGP).
Forward the best path to the optimal path to find the diameter. The router is first lookup in the routing table, and it is determined that you know how to send the packet to the next site (router or host), if the router does not know how to send the packet, it usually discards the packet; otherwise groups according to the corresponding entry of the routing table Send to the next site, if the destination network is connected directly to the router, the router is sent directly to the corresponding port. This is the routing forwarding protocol (ROUTED Protocol).
Routing forwarding protocols and routing protocols are mutually cooperative and independent concepts. The former uses the latter maintained routing table, and the latter should use the functionality provided by the former to issue routing protocol data packets.
Doubt:
1 conflict domain and broadcast domain
Conflict domain: Each node in the same conflict domain can receive all transmitted frames based on the first layer.
Broadcast Domain: The collection of all devices of the broadcast frames that can receive any devices in the network are based on the second layer.
The cause of conflict domain is the working principle of the CSMA / CD, that is, the port is listened to the port, waiting for the network to be sent again, and the hub is a shared network, so when the number of terminals, the maximum number of terminals The easier conflicts are created. The generation of the broadcast domain is due to the fact that the data frame is forwarded at the second layer, and the data frame is broadcast in the network in the network to find the destination MAC terminal. (ARP, RARP also broadcasts, ie unknown Macs generally broadcast). In the shared network, a physical network segment is a broadcast domain. In the switching network, the broadcast field can be a virtual network segment with a set of any selected second-layer network address (MAC address). 2 network bottleneck
About the GPRS bandwidth is not a way to achieve G grade, the server generally connected to the network is used to use Ethernet technology. It follows the rules of the CSMA / CD, so it is easy to form a network bottleneck, which can be solved by isolation conflict domain. Generally, it is difficult to reach G-class, and the number of users will be a bandwidth of Grades.
