Overview Computer Network
LAN : small-coverage, a room where the machine is connected through a convergence layer and access layer switch switches, cable room where no more than 100 meters, and the access switch cable length aggregation switch is not more than 100 m, the signal does not decay, the data access layer switch out broadband larger, if the access port is 100M, the convergence layer out port requires 1000M port, thus constitutes a star configuration.
WAN
relatively far distance, to spend money to rent the bandwidth, if the user via ADSL or fiber access or otherwise, is a WAN bandwidth with the increase in the cost becomes larger,
Internet
from the ISP (internet service provider) composed of operators inter also be connected via broadband 100000M data, the server can also be accessed via the user's global ISP access, different users access to different ISP ISP servers will be data bandwidth limitations between operators, resulting in slower access, of course server It can also allow users to provide two-wire or multi-line service access
computer data communication process
planning IP address to communicate via ip address, resolve domain names to IP addresses to send data requests to the DNS server through a locally configured DNS server addresses, LAN computers to communicate internally through a gateway router, each device has a unique MAC address of the interface, called the physical address,
the packet data frame and
the packet includes a source address and destination address, the router first thrown out the packet transfer , this time you need a computer Physical address and the physical address of the router (the MAC), the maximum 1500 byte data packets,
data framesOn the basis of the data packet is added on the source and destination physical address physical address, next, to find the target router address (IP), then modifies the physical address of the source and target physical address, but the packet will not change, physical addresses with different delivery devices varies, the packet reaches the destination decision, and determines what physical address reaches the router device,
visit data
server sends the data packets, the maximum 1500 bytes, cut into a plurality of packets, transmission code on the number, the card has a cache computer, receive buffer, data transmission buffer has, when sending the transmission remains in the cache of the card, the card when the client receives the first packet, send a message to the server Please send a second, and then the server NIC cache of the first packet can be removed to free up space, sequentially stored in the cache, followed by the release of cache, followed to the end, the data card in the client's cache to start sending a web page data packets put together, and then release the card cache
The OSI reference model
was divided into seven layers became, sequentially from the bottom layer to the top layer of the service
application layer : all programs can generate network traffic
that layer : whether encrypted or compressed prior to transmission processing such as the page image can be transmitted in the first cut into the compression packet is sent, or the site will be encrypted and then cut data packet is sent, the presentation layer if an error occurs, the page will display an error, such as server-side use ASCII code compiler, and clients in other ways compile error occurs.
Session layer : a web server and communicate that session. Or Trojan horse can check netstat -n netstat --nb
transport layer : a reliable transport (TCP, a case where the buffered data packets in the card case without feedback or other data loss in the network can be sent again), flow control, unreliable transport (UDP packet transfer). TCP header plus data called a data segment or news
network layer : responsible for choosing the best path, IP address planning, there are IPV4 IPV6 ARP ICMP IGMP. IP header plus TCP data called packets and
a data link layer : the beginning and end of a data frame, transparent transmission, error checking. MAC header plus the IP TCP data and FCS (check value) referred to the data frame
physical layer : the network device interface standard, Ethernet, ATM, Frame Relay, electrical standards (such as voltage), how to transmit faster physical link speed.
the OSI reference model for network troubleshooting guide
see if the card state of the physical layer fault, connection status, transmit and receive data packets
Fault data link layer, MAC address authentication, MAC address conflict, the ISP supplier arrears, speed mismatch, 100M mismatch 1000M, VLAN computer is connected to the wrong VLAN
network layer failures, planning address, select the path, the configuration incorrect IP address, subnet mask, gateway configuration error, the router does not reach the destination routing address configuration
application layer failure: application configuration error,
the OSI reference model and network security
physical layer security, turn off unused ports
datalink ADSL account password security layer, data link layer security, VALN switch port binding MAC address of the
network layer security, the ACL control packet traffic on the router, a firewall
application layer security, application development without flaws