RS Review: Two-layer technology----Ethernet

The OSI communication model divides the network communication into 7 relatively independent functional levels---application layer, presentation layer, session layer, Transport layer, network layer, data link layer and physical layer. (This picture is ugly ....) ）

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The physical layer is responsible for transmitting bitstream, using high and low pulse circuits to represent 0 and 1, not within the scope of SWAIIOW research.

The Data Link layer (OOL) has two responsibilities: send and receive, at the same time, also provide data effective end-to-end transmission connection (PPP what), the data link layer is responsible for the instruction, data, etc. encapsulated into the frame (Zhen son, en (⊙v⊙)), the frame is the structure of the link layer, he must contain enough information (who I am, who I want to send) To ensure that the data is transferred to the destination safely and securely through layer two.

So, from this point of view, each data frame needs to have the most basic:

1, as a courier, I want to know who shipped, who received the goods

2, I send is what, the total tell people what is in the car is what is it?

3, check, or someone else to send an iphone, hand turned into a stone

At the same time, as a courier, workflow is like this: the above all kinds of big guys, what to do, I only see the customer---Network layer to my package, and then I bear the load of hard work, and throw to the following physical layer----tall guy and Humpty Dumpty, walking a winnow ...

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(This picture is ugly .....) ）

If you want to look at the details as a courier, how many things to carry ....

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/(ㄒoㄒ)/~~ true TM many .... They are like this one layer by layer inserted ... Insert.... Insert

First of all, take a look at Ethernet, the largest courier company:

Ethernet Although as the largest express company, below also has several small branch

Ethernetⅱ, Netware, 802.3 SAP, 802.3 LLC SNAP, as a branch office, we carry out the courier standards should not be changed, the approximate process is like this

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So for our express company, the customer carrying what, I am not so concerned about, I only use in the end to increase the number of express, ah, check what.

At the same time, we have the package size is required, the requirements of the foreigner head office is such

Ethernet Frame

Here we discuss both legal and illegal Ethernet frames. The receiver would drop all illegal frames.

The vast majority of all local (LAN) data traffic in the world is Ethernet frames!! There is no. A single unit of data, and more common. So anyone in any type of technical field would benefit by understanding the contents of these frames, and how they is TRA Nsmitted and received.

Min Frame Size = header+crc+datamin = 64
Max Frame Size = Header_crc+datamax = 1518

Simply put, the head office requires:

1, package must be legal, or I do not

2, the package can not be too small, can not be too large, the size must be between 64 to 1518, if less than 64 I can not pass, if more than 1518, I have to consider whether to send two parcels, if the customer does not let (DF set, not allow shards), that no way, can only discard

Since here, the parcel size can only rely on the user, the user data is large, we also have to preach Ah, let not send multiple parcels, is also the user's decision-making thing, to understand the business, we must first look at our Express is written, the front also mentioned, the Express must contain:

Who delivery, who receive goods, delivery content, calibration, the Express company to express the number of the wording of the different, to a general overview:

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As can be seen from the above, in the Ethernet, we use the MAC address as customer shipping, delivery address

Let's start with the Ethernetⅱ company first, take a look at the detailed package

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The function of each field is already obvious, here is a thing, the length of each field is added 6+6+2+4=18bytes, so the customer wants to send the goods (data) part, the minimum is 46, the maximum is 1500

The Type field indicates what is being hosted, and the content that can be hosted is roughly the following (En ... Who TM remember Ah .... ), remember a few key on the line, such as IP, ARP, RARP, MPLS and so on, here you can also find a problem-----ARP This protocol is not three layer, oh, before the interview asked, ARP work in which layer, Connaught, three layer of the agreement has told you type=0x0800, The ARP protocol family is listed separately, and then look at MPLS VPN, as a tagged party, working between two or three layers, so, we can say that ARP works on the second level.

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NetWare Express Company:

The package is like this

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1. Change the Type field to length

2. Change the Type field to DSAP and SSAP

3, load can load less point 6+6+2+1+1+4=20

802 group companies are almost

You look at 802.3SAP.

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You're looking at 802.3 LLC.

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Oui, is sold to the manufacturer, 24 bit,22 bit can sell, the last 2 bit to indicate unicast or multicast

And, 802.3 head, use Lenth to be different from Ethernet two frame, length valid value is 0-1536 (ie 0x600)

Then the Ethernet two frame to avoid this value segment, if greater than 0x600, then the Ethernet two-type frame, less than 0x600, is 802.3

since 802.3 header has no type field, it is supplemented by 802.2来 (also known as LLC)ISOwill be2layer is divided intoLLCLayer+maclayers, different protocol areas are divided into differentMAClayer, but the common oneLLClayer, like this

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Actually write so much (╮ (╯_╰) ╭ you have the nerve to say much .... ), mainly remember the following points

1, the data frame transmission on the Ethernet must be legal, otherwise it will be discarded

2, the data frame size must be between 64-1518, less than this can not be transferred, greater than this to be fragmented

3, several packages of subtle differences, the switch uses lenth length to determine the format, greater than 1536 is the Ethernet two frame, less than 1536 is 802.3 of the frame

4, ARP is not a three-layer protocol AH

Attached: http://www.infocellar.com/networks/ethernet/frame.htm

A foreigner's article about Ethernet frames, good

This article comes from "Blood and glory!" "Blog, be sure to keep this provenance http://65191212.blog.51cto.com/5376954/1738889

RS Review: Two-layer technology----Ethernet