A domain name protocol DNS (Domain Name System)
function: the domain name to an IP address. For example, hit the open QQ (can directly use the IP address of the landing), open network may be the domain names.
8.8.8.8 is google's DNS server, 222.222.222.222 telecommunications DNS server can be used to help resolve the domain name address.
6.1.2 Domain Name
Root.
Top-level domain com, edu, net, cn, org, gov
two domain names 91xueit, inhe, for example 91xueit.com is globally unique domain name.
Third-level domains dba, for example www.dba.91xueit.com
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Ping or nslookup to get the IP address. Or directly enter the URL.
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II Dynamic Host Configuration System DHCP (same network segment)
(1) a static IP address
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(2) dynamic IP address
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(3) DHCP client requests an IP address of course
I understand that this is a request and allocation process dynamic IP addresses. Made in the web client request to the broadcast address, the destination IP is 4 255, the destination MAC address is all FF. After receipt of DHCP, the address will be selected from a pool to the client. If your network has two DHCP server and gave feedback, this time the computer is also a need to return data to inform him who chose the address provided. Another DHCP client was found not to be his, then withdraw his offer. From this perspective, the network can not have too many DHCP server.
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(4) mounted DHCP server
must be a fixed IP address. Release command ipconfig / Release
(5) DHCP IP address inter-network configuration
requires a computer with DHCP IP addresses, you need to configure IPhelper address on the gateway router network where he was, then access to DHCP.
6.3 File Transfer Protocol the FTP (File Transfer Protocol)
6.3.1 use the FTP two TCP connections
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FTP connections comprises a control and data connections. Each upload / download a file it will establish a session.
Control connection: 21 is the standard port for transmitting the FTP command information.
Data Connection: 20 is the standard port for uploading / downloading data.
Three, FTP data connection (data on a TCP connection in FIG.)
Related to active and passive modes
(1) Active mode: FTP client tells the FTP server (port 21) it is what the port listens, then FTP server (port 20) actively and FTP client this port to establish a connection .
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(2) Passive mode: FTP server to open a new port (e.g., port 1089) in the specified range and listens passively waiting for the client to initiate a connection.
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summary, in the case of a firewall, if you use the passive mode, the firewall had to open multiple ports to listen. Therefore the active mode should be used for data connection and the firewall 20 and port 21 open.
Four, FTP transmission mode
Text Mode: ASCII mode to transmit a sequence of text data.
Binary Mode: Binary mode, binary data sequence transmission.
Fifth, the remote terminal protocol telnet
TDP23 default port.
Sixth, the Remote Desktop Protocol RDP (Remote Desktop Protocol)
6.6 Hypertext Transfer Protocol HTTP (Hyper Text Transfer Protocol)
Visit the Web site through this agreement.
Seven, the World Wide Web www (World Wide Web)
(1) www providing distributed service
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(2) Uniform Resource Locator System URL (Uniform Resource Locator)
a bit like an address.
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identifies the site of a variety of ways, different ports, different IP addresses, different domain (host headers) to distinguish.
Eight, using a web proxy server to access the site
Other hosts within the network can not be accessed by routing Internet, this can only be accessed by a web proxy web proxy (on the same network segment) to access the Internet and other hosts within the network to achieve Internet access. If the web proxy outside the network, but more slowly.
(1) to save bandwidth within the network to access the Internet (easy access to the contents of small changes in the website).
(2) to bypass network access outside the firewall. For example, to visit a banned site A, but if A by the same network of web proxy, you can access the site.
(3) to avoid being tracked by a web proxy.
Nine, e-mail (SMTP, POP3, IMAP)
Of the SMTP, POP3 and IMAP is closing.
