Shulou(Shulou.com)06/02 Report--

The origin of the switch starts with Ethernet:

Ethernet / LAN (local area network):

There is a problem:

The signal transmission distance is limited.

Solution:

Repeater-amplifies the electrical signal to extend the transmission distance of the information

Problems caused by repeaters:

Only 2 ports with few connected devices

Solution:

Hub-A multi-port repeater that can connect multiple devices

Problems with hubs:

The signals sent by different terminal devices will conflict.

Mitigation scheme for signal conflict:

CSMA/CD, with collision detection, carrier sense multiple access mechanism

Introduce a new device: bridge (bridge)-isolate collision domain

Bridge problem:

Bridge devices have fewer ports and can only connect 2 devices

Solution:

Introduce a new device: switch-multi-port bridge to isolate the collision domain

The above is a history of our switch.

How the switch works:

1. First check the "destination MAC address" of the packet

2. Match the destination MAC address with the entry in the MAC address table

If it is successful, it will be forwarded out the corresponding port

If it fails, broadcast (out of all ports except the incoming port)

1. What is the MAC address like?

Length is 48bit

Represented by hexadecimal

Structure:

Vendor Code-24bit

Own code-24bit

(the number of the network card produced by each manufacturer)

Packet structure:

Source MAC-destination MAC

Source IP-destination IP

2. What does the MAC address table look like?

Each entry is the correspondence between the MAC address and the Port

Data that is destined for the MAC address is sent from the corresponding Port

How the MAC table is formed:

Static configuration

Dynamic learning-

1. After the switch receives the packet on the port, first check the

Source MAC address, thus forming the correspondence between the source MAC and the incoming port

2. Analyze the destination MAC address of the packet and look up the MAC address table

-if the corresponding MAC entry can be found, it will be forwarded at the corresponding port

-if the corresponding entry is not found, broadcast

3. How do the two match?

Show MAC address tabl

SW1# show mac-address-table

4. Survival time of dynamic entries in MAC table:

300 seconds.

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