Shulou(Shulou.com)06/01 Report--

I watched the second video last night. Here is a brief summary.

First, start with bytes

Bit is made up of 0 and 1.

8bit=1 Byte

Second, the main points of data link layer packets.

1. Destination mac+ source mac+ type 6 bytes + 6 bytes + 2 bytes

2. The size of the mac address is 6 bytes

So the packet size of the data link layer is 14 bytes.

There's an extension here about the difference between 802.2, 802.3 and Ethernet 2.

802.3 of the packets do not have a class model, which leads to a multiplexing problem, so 802.3 of the packets must be followed by a 802.2, that is, llc (logical-link control). Through the asdp and ssap and control in 802.2 to indicate that there is in data type 802.2 (snap is public and asp is private)

But Ethernet 2 has a class model, so it doesn't need to be followed by 802.2 packets.

III. Network layer

A 20-byte ip layer is mainly source ip, destination ip, class model (most important) ip address is 4 bytes

The role of ip is routing

The destination and source address of the packet transmission remain the same. Mac changes.

IV. Transport layer

20 bytes

Mainly port number

Explanation of common problems

1. The concept of bridge is equal to one software switch, one device and two ports (one in and one out).

2. The switch is equal to a fabric

3. Why does the switch work at the data link layer because it works according to the mac of the data link layer

4. Why the router works at the network layer is because it works according to the ip of the network layer.

5. Broadcasts cannot pass through the router

6. The difference between a router and a layer 3 switch is that a wan connection equals that a layer 3 switch cannot do nat

7. Analyze the usage of acl. Acl means to control the network layer ip and transport layer ports.

8. Tcp has flow control and reliable connection. Udp and tcp each have their own advantages. Which is the best?

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