TCP/IP Knowledge Summary (TCP/IP protocol family reading Note II)

Next, summarize the network layer protocol,IP,ARP,RARP,ICMP,IGMP. When we are in the process of network transmission, the delivery of packets to the host or router requires a level two address: Physical address and logical address. And we need to be able to map the physical address to the corresponding logical address, and the reverse mapping is also necessary.

There are two concepts involved: static mapping and dynamic mapping .

Static mapping is the creation of a table that associates a logical address with a physical address, which is stored on every machine in the network. However, the physical address of the machine that exists in the network is often changed (replacing the network card), so that the static mapping table has to be updated constantly, affecting the performance of the network.

Dynamic mapping is when the machine knows one of the addresses, it can find another address through the protocol. ARP and RARP are required to complete the dynamic mapping!

I. ARP (Address Resolution Protocol)

ARP is the logical address mapped to a physical address, ARP requests are sent by broadcast, the answer is sent by a single advertisement.

Two. RARP (Inverse Address Resolution Protocol)

Rarp is to map the physical address to a logical address, the RARP request is sent by broadcast, the answer is sent by a single advertisement.

Three. IP (Internet Interconnection Protocol)

IP is the transmission mechanism, unreliable, "best effort" of TCP/IP. When reliability is important, IP must be used in conjunction with TCP.

VER: Version

Hlen: Header Length

Time to live: datagrams must have a limited lifespan when passing through the Internet. Originally intended to hold a timestamp, the value was reduced by 1 by each route passed. This datagram is discarded when the value of the timestamp changes to 0 o'clock. But then all the machines have to be synchronized, and the time of the data from one machine to another is known. So now this number is used for the maximum number of hops that the datagram is routed through.

Protocol: 1-->ICMP,2-->IGMP,6-->TCP,17-->UDP. Define high-level protocols that use the IP layer service

　　Shard-related fields:

　　Identity:

Flag: 3 bits, first reserved for later use, second bit "not Shard", if 1, indicates that the datagram cannot be fragmented. Finally thought is "Shard".

Shard Offset: This is the offset of the data in the original datagram.

Test and: The error detection method used in most TCP/IP protocol families is test and. Verify and be able to protect the damage that the packet is subjected to during transmission. Inspection and is the information that is attached on the group.

Four. ICMP (★ ¡ï Internet Control Message Protocol)

The IP protocol lacks error control and auxiliary mechanism . ICMP is designed to compensate for the above two points. In fact, the ICMP packet is first encapsulated as an IP datagram and then passed to the next layer. ICMP packets are divided into two categories: Error reporting messages and query packets.

One error report message:

3--> end point is not reached; 4--> source point is suppressed;

11--> timeout; 12--> parameter problem;

Inquiry message:

8 or 0--> echo request or answer 13 or 14--> timestamp request or answer

17 or 18--> address Mask request or answer 10 or 9--> routing inquiries and Notices

ICMP Error Reporting message:

ICMP always reports the error report message to the original data source;

ICMP error messages are no longer generated for datagrams carrying ICMP error messages;

For the datagram of a shard, if it is not the first Shard, no ICMP error message is generated;

ICMP error messages are not generated for datagrams with special addresses (127.0.0.0 or 0.0.0.0)

Five. IGMP (Internet Group Management Protocol)

The IP protocol can be used in two types of communication: Unicast and multicast (the same message is sent to a large number of receivers at the same time). IGMP is a necessary but insufficient protocol for multicasting. There are 3 message types in IGMP messages: query, Membership report, and exit report .

　　

　　

TCP/IP Knowledge Summary (TCP/IP protocol family reading Note II)