CCNA (4) data link layer and switch

1. Functions of the data link layer

Implements data error-free transmission. It receives raw data from the physical layer to form frames and bit groups) and transmits data between network devices. The frames contain the physical addresses of the active and target sites, the device that works on this layer has a switch.

2. Ethernet

To put it simply, we usually use an Ethernet LAN that includes Ethernet)

Strictly speaking, Ethernet works at the data link layer.

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Signal conflicts over Ethernet are solved by using CSDA/CD (Multiple Access Channels for carrier listeners with conflict detection ).

1> If the middle line is shared, who will use this line at the same time?

2> ensure that these hosts can use shared lines in an orderly manner without data conflicts

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3. the MAC address of Ethernet is unique) (physical address in Ethernet)

1> an ethernet address is used to identify a single device or a group of devices on an Ethernet network.

2> 48-bit binary (usually expressed in hexadecimal notation)

3> generally, it is divided into two parts: Supplier ID and serial number.

For example:

00-06-1b-e3-93-6c 00-0d-28-be-b6-42

IBM OISCO

Supplier ID

--> MAC address definition (addressing)

Host A sends A data or data stream to host B to determine whether the host is in my network. At this time, there must be an address.

--> Unicast and multicast of MAC addresses

Unicast: the data sent to the MAC address must have only one acceptor.

Multicast: data sent to MAC addresses, with multiple receivers

--> Differentiate unicast

The eighth digit is used to distinguish 0-physical address unicast) 1-logical address Multicast)

4. Ensure that the recipient of the sent data can receive and identify the data in the network, involving

Data link layer: Data Format frame)

802.3 Ethernet frame format:

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| -------------> Encapsulation of the data link layer <------------ |

| ---------------------> Physical layer encapsulation <-------------------- |

--> Meaning of the Two-byte type/length

Type refers to the protocol type applied by the upper layer.

If the value is greater than 0600 H, the type is smaller than 0060 H, indicating the length.

The minimum data transmission byte is 46 bytes.

5. Data Link Layer

1> Logical Link Control Sub-layer LLC) -- 802.2

2> Media Access Control Sub-layer MAC) -- 802.3

Illustration:

Network Layer
Data Link Layer	LLC sublayer
	MAC Sub-Layer
Physical Layer

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--> Problems solved by the MAC Sub-Layer

Media Access Control MAC) Sub-layer 802.3)

1> encapsulate the data handed over by the upper layer into the opposite process when the frame entry is sent and received, and split the frame)

-- Encapsulation of bits into data frames --

2> implement and maintain media access control protocols, such as CSMA/CD and bit error detection

3> MAC frame addressing, that is, the origin site of the MAC frame), and the Origin Site of the MAC frame)

--> Problems solved by the LLC sublayer

Logical Link Control LLC) sublayer 802.2)

1> establish and release a logical connection to the data link layer

2> Provide SAP at the interface network layer and link layer with the upper layer)

3> Add the sequence number to the frame

6. Ethernet naming

N-signal-Physical Medium

N: data transmission rate in megabytes, such as 10 100 1000

Signal: baseband or broadband

Physical Media: indicates the media type

Illustration:

100 BASE-TX

100: data transmission rate: 100 M

BASE: baseband transmission

TX: Transmission Media

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--> Baseband BASE)

The physical media of Ethernet is used to transmit Ethernet data.

--> Broadband (BROAD)

In addition to Ethernet traffic, there are other traffic, such as voice and video traffic, which are used for sharing.

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7. Ethernet Switch

A switch is the main device used to connect to a LAN.

1> the switch can intelligently forward data based on the destination address in the Ethernet frame. Therefore, the switch works at the data link layer.

2> switch division of conflicting domains to improve transmission rate) to achieve full duplex communication

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8. vswitch data forwarding Principle

-----> Switch-based thinking <-------

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9. Ticket, half duplex, full duplex

1> Ticket: there is only one channel, and the transmission direction can only be one-way

2> half duplex: there is only one channel. At the same time, only one-way transmission is allowed, for example, walkie talkie)

3> full duplex: dual-channel and bidirectional data transmission

10. Switch internal switch mode

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11. vswitch Configuration Mode

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Labs involved:

Vswitch access method

Vswitch startup