▶ Link layer fifth ◀ Ethernet LAN with broadcast channel (lower)-------

Ethernet LAN with broadcast channel (down)--------- frame format (MAC)

L Hardware address (Mac address ) of the MAC layer

In a local area network, the hardware address is also called the physical address, or the MAC address. ( address of the location)

The "address" as stated by the 802 standard should be strictly the "name" or identifier of each station.

In fact, our textbook address is not very accurate, but we are accustomed to this type of "name" is called "address", so this book is also used in this idiom.

ieee RA  responsible for assigning the first three bytes of the Address field to the factory ( Span style= "font-family: ' Times New Roman ';" >24  bit ) Span style= "font-family: ' The song Body '; >

The latter three bytes in the Address field ( that is, the low -level ) are assigned by the manufacturer, called the extension identifier, and must be guaranteed that the produced adapter does not have duplicate addresses.

A block of addresses can generate 224 different addresses. This type of address is called MAC-48, and its generic name is EUI-48.

The "MAC Address" is actually the adapter address or adapter identifier EUI-48. It was burned in our network card before the factory. This address is not to be changed.

L Adapter Check MAC address

The adapter first checks the Mac address in the mac frame with hardware from every mac frame received on the network .

If it is sent to the site of the frame is accepted, and then other processing. Otherwise, the frame is discarded and no additional processing is done.

"frames destined for this site" includes the following three types of frames :

Unicast (unicast) frames ( single-to-one)

Broadcast (broadcast) frame (one-to-all) (full 1 address)

Multicast (multicast) frames (one-to-many)

L MAC frame format

Common Ethernet MAC frame formats are available in two different standards:

DIX Ethernet V2 standard

IEEE 's 802.3 Standard

The most commonly used MAC frames are the Ethernet V2 format.

MAC frame V2 format

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In order to achieve bit synchronization on the transport media, the actual transfer is 8 bytes More than the MAC frame

l Invalid MAC frame  

When the adapter receives a mac frame, it checks to see if it is a valid mac frame.

ü the length of the frame is not a whole number of bytes;

ü test sequence with received frame FCS isolated with error;

ü the length of the data field is not between the ~ bytes.

ü A valid MAC frame length is between ~ 1518 bytes.

For invalid MAC frames checked out, simply discard them. Ethernet is not responsible for retransmission of discarded frames.

L minimum inter-frame interval             

The minimum interval between frames is 9.6 ms, which is equivalent to the send time of the.

When a station detects that the bus is starting to idle, it waits for 9.6 ms to send the data again.

This is done so that the receiving cache of the station that just received the data frame is cleaned up and ready to receive the next frame.

Extended

"extended one"mac address conflict and view change mac address

If you have the same MAC address in a local area network (under the same switch connection) , it can cause a conflict, causing the party not to be able to surf properly.

We say that the mac address is engraved in the NIC adapter, is not possible to change, but we can specify a mac address, so that the application of the specified mac address, Without a fixed MAC address on the NIC

See the MAC address below

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Manually specifying MAC addresses

Local Area Connection --- change adapter settings --- Local Area Connection Properties --- configuration ---- Advanced --- Network Address (locally administered address)

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Check the MAC address After you've specified it.

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found that the mac address did change to the mac address we specified.

"Extended two" uses the Grab tool to grab mac frames and view the composition of Mac frames.

In the virtual machine PC0 shared a tt.txt file, the contents are all tttt ....

This file is then found in the PC1 with the capture kit installed and then copied to the PC1 desktop. In this process, the data packets are crawled as follows :

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You can easily understand the format of MAC frames.

Packet capture analysis is very important, can be used to troubleshoot the network, here first to understand, when the TCP/IP will focus on.

                                                                                                   

This article is from the "Huan Blog" blog, make sure to keep this source http://zhaoyuqiang.blog.51cto.com/6328846/1577150

▶ Link layer fifth ◀ Ethernet LAN with broadcast channel (lower)-------