Data packet is transmitted in TCP/IP OSN 8800 communication protocol data unit, a single message is divided into a plurality of data blocks, the block
of data called a package, which contains the address information of the sender and receiver. The package
and then along different paths in one or more of the network transmission, and reassembled
at the destination.
Structure data, the data packet is very complicated, here mainly about its key
componentscan be, it is very
important for the understanding
of the principle of TCP/IP protocolcommunication.
The packet is mainly composed of the destination IP address, source IP address, payloaddata and other parts, structure of data packets and we
usually write very similar, the destination IP address that the packet is to be sent to the who, the equivalent of the recipient address, IP source address that the
packet is from where, quite the sender
address, andpayload data is
equivalent to the content of the
letter.
Two, it is because the data packets having such a structure, installation of the TCP/IP protocol between computer can communicate with each other. We based
on the TCP/IP protocol network when
in use, the network transmission of data packet is in
fact.
To
understand the data packet, is of critical importance to the network security of network management, you get
online open webpage, this simple act, is that you have to send data packets to the site, after it receives the transmitted
data packets, according to your IP address, return to your webpage data packet, that is to say, the webpage browsing, is actually to exchange data packets.
Three, packet filtering is sometimes referred to as static packet filtering, it analyzes theafferent and efferent and data
packets according to the
established standard transfer or block packets to control access to the network, when the router according to filter rules for forwarding or reject packet, it will
serve as a packet filter.
When a
packet arrives on the data packet
filtering router, the router will extract someinformation from the packet header, according to filter rules determine the packet should bepassed or should be discarded. Packet filtering work in the network layer of the open systems interconnection model, or Internet layer TCP/IP.
Four, as the third layer of equipment, data packet filtering router based on the source and destination IP address, source port and destination port and protocol
of data packet, use the rules to determine should allow or reject flow. These rules are defined using the access control list, ACL is
a sequential list a series of
permit or deny statements, is applied to the IPaddress or the upper layer protocol. ACL can
extract information from the packet header,tested according to the rules, and then decide to allow or reject.
Through the
data packet capture software, can also be the data packet capture and analysis.Is to use packet interface diagram, capture software Iris to
capture data packets on this, we can clearly see the captured data packet MAC address, IP address, protocol type, port number and other details, through the analysis of these data, SL4D the network administrator can know the network exactly what kind of data packets in the activity.
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