Networking basics
network reference model
OSI (open system interconnection) seven-layer model of
computer networking features: data sharing, data communications, data security, data processing capabilities
hierarchical thinking: the decomposition of complex processes, simplify complex issues; easier solving specific problems and found that
the 1984 international organization for standardization (ISO international standard organization) enacting
functions of each
physical layer: the establishment, maintenance, physically disconnected (the definition of medium and the interface, the transmission bit stream) card
data link layer : establishing a logical connection, hardware address addressing, error checking (switch), a frame
network layer: logical address addressing, routing implemented (router) packet data packets between different network
transport layer: the definition of transmission of data ports number, as well as flow control and error checking, to achieve a connection with the program (firewall) is called a data segment a data segment
session layer: establishing a session termination management (HTTP)
presentation layer: data indicating security, compression
application layer: network services and end-users an interface
A predetermined binary number one bit (bite), 8 bits in a byte, a bit stream is formed
MAC address: a group ID on the card, called a data frame (frame), stp protocol
Ip protocol
connection-oriented reliable protocol Tcp protocol, udp protocol without connection-oriented protocol unreliable; each program has a special identification number is the port number
Tcp / IP protocol suite
four models: a network interface layer; network layer; a transport layer; application layer
five models: The physical layer; data link layer; network layer; a transport layer; application layer (up to the actual use)
application layer: http; ftp; tftp; smtp ; snmp; dns
transporting layer: tcp; udp
network layer: icmp; igmp; ip; arp; rarp
Data encapsulation and decapsulation
encapsulation process of the data from top to bottom:
the application layer: Upper Data
Transport Layer: TCP header + data upper
network layer: IP header TCP header + data + upper
data link layer: MAC header + IP + TCP header portions header + data upper
physical layer: forming bit stream
decapsulation process data from the bottom to the top: in turn
Protocol data unit (PDU) bit stream, data frames, data packets, data segment
Number System
Number System: A method of digital manifestation count
digit: digit symbol is located in a position numbers
Base: In certain number system, the number of digital symbols can be used by the digital
bit weights: a means species number system, the number of bits represented by the size of the
conventional numbering system:
binary: every two B into a
decimal: a D every decimal
hex: every fifteen H into a
conversion between binary and decimal:
1 1 1 1 1 1 1 1（B）
128 64 32 16 8 4 2 0（D）
IP addresses and their classification
Subnet Mask: 1 represents a continuous network bit, on behalf of the host consecutive 0-bit
host-bit IP address are all 0 for the network number
Host IP address bits are all 1 represents the broadcast address