Shulou(Shulou.com)06/03 Report--

I. introduction to the functions of the network layer:

The main function of the network layer is to transfer data from the source to the destination.

2. IP packet format:

1. Version: this field contains the version number of IP, 4 bits. The current version numbers are IPv4 and IPv6, and here is IPv4.

2. Header length: this field is used to indicate the IP packet header length, 4 bits. The minimum length of the IP header is 20 bytes, but its length is variable, depending on the length of the optional field.

3. Priority and classification: this field is used to indicate the priority and service type of the packet, 8 bits. By dividing a certain priority in the data packet, it is used to achieve the requirement of quality of service.

4. Total length: this field is used to indicate the length of the entire IP packet, 16 bits. The maximum length is 65535 bytes, including packet headers and data.

5. Identifier: this field is used to represent the identifier of the IP packet, 16 bits. When IP fragments the upper data, it assigns a set of numbers to all the fragments, and then puts these numbers into the identifier field to ensure that the fragment will not be mistakenly reorganized by the identifier field to identify a packet, so that the receiving node can reorganize the fragmented packet.

6. Logo: flag field, 3 bits. Logos and fragments are used to convey information. For example, when a packet is sent from one Ethernet to another, it indicates that the current packet cannot be sliced or a packet is sliced to indicate whether the last shard in a series of shards has been sent.

7. Segment offset: this field is used to indicate the segment offset, 13 bits. The information contained in the segment offset is how to reconnect the fragments in a fragment sequence.

8. TTL: this field is used to indicate the life cycle of an IP packet, 8 bits. This field contains information that prevents a packet from being forwarded through the network indefinitely.

The meaning of the TTL value is the maximum turnaround time that a packet can experience in the network before it is abandoned. Each router through which the packet passes checks the value in this field, and when the value of TTL is 0, the packet is discarded.

TTL corresponds to the number of packets passing through the router. Each time a packet passes through a router, the TTL subtracts 1.

9. Protocol number: protocol field, 8 bits. This field is used to indicate which protocol is encapsulated in the IP packet, whether it is TCP or UDP,TCP. The protocol number is 6 and the number of UDP is 17.

10. The first checksum: this field is used to represent the checksum, 16 bits. A checksum is a 16-bit error detection field. The destination host and each gateway in the network recalculate the checksum of the packet header, just as the source host does. If the data has not been changed, the two calculations should be the same.

11. Source IP address: this field is used to indicate the source address of the packet, 32 bits. This is a network address, which refers to the network address of the device that sent the packet.

12. Destination IP address: this field is used to indicate the destination address of the packet, 32 bits. This is also a network address, but refers to the network address of the receiving node.

13. Optional: optional fields are of variable length according to the actual situation, and there are several options that can be used with IP. For example, you can enter the time when the packet was created, and so on. After the option, there is the upper data.

Third, the full name of IPCM protocol is Internet control message protocol, which is mainly used to send control messages in IP network and provide feedback on all kinds of problems that may occur in the communication environment. Through this feedback, the administrator can make a judgment on the problem, and then take appropriate measures to solve the problem.

IV. Packaging of ICMP

5. Common parameters of Ping command

1. In a Windows system, four ping packets usually occur. If you add-t to the ping command, the system will continue to ping all the time. Press and hold Ctrl+C to interrupt the command.

2. In the Windows system, add-an after the ping command to return the hostname between places.

3. In general, the size of the ping packet is 32 bytes. You can add-l plus byte length after the ping command.

VI. Brief introduction of ARP

ARP- address Resolution Protocol, its basic function is to resolve a known IP address to an MAC address so that it can communicate through the MAC address on the switch.

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