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Definition of a network: a set of intermediate systems (network devices) that use media (cables) to interconnect, as well as end systems (PCs and servers).

The meaning of the network: resource sharing is achieved by letting the application pass information to each other.

The hub can be understood as the earliest switch, a 1-tier device that does not recognize any control information, and the forwarding mechanism is amplified signal + flood processing. All devices connected to the hub have a conflicting domain. The hub's interface always supports only half-duplex transmissions.

Conflict domain: The set of devices that can receive conflict fragments when a conflict occurs is a conflict domain.

Broadcast domain: A collection of devices that a broadcast message can affect. All devices connected to the switch (including switches) are in the same broadcast domain (network segment).

Switch , which means "switch", is a network device used for transmitting electrical (optical) signals to any of the two networks connected to a switch. node provides a unique electrical (optical) signaling pathway.

The switch works on the second layer of the OSI Reference Model, the data link layer. The CPU inside the switch is connected to each port successfully, and the MAC address and port correspond to form a Mac table. In future communications, packets destined for that MAC address will be sent only to their corresponding port, not all ports. Therefore, the switch can be used to divide the data link layer broadcast, namely the conflict domain, but it cannot divide the network layer broadcast, namely broadcast domain.

MAC Address (Media Access Control) that defines the location of the network device.

Cam Table (content addressable memory), contents addressable storage.

The so-called cam table, which is a table maintained in memory by Cisco IOS running on a two-layer switch, is the table where the switch forwards data at Layer two to look for, the table with the MAC address, the corresponding port number, the VLAN to which the port belongs, and the type (STATIC or DYNAMIC).

Switch#show mac Address-table

Mac Address Table

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Vlan Mac Address Type Ports

----    -----------       --------    -----

In addition to dynamic learning, the MAC Address table of a switch can be statically specified manually. When the switch forwards the data, it needs to make corresponding forwarding according to the Cam table, if the target host's MAC address is not in the table, the switch will use flooding to obtain the target host's MAC address and join the cam table. One interface of a switch can correspond to multiple MAC addresses, with no limit on the number of addresses, but no more than the maximum number of MAC addresses supported by the switch lock. After the switch learns the MAC address on an interface, the mapping of the address to the interface is not always saved in the Cam table, unless it is statically specified manually. When a host is transferred from an interface, it makes no sense for the switch to make a mapping of the host MAC address to that interface, so the MAC address has the largest dwell time in the cam table, called the Aging Timer (aging-time), The MAC address is deleted when the corresponding MAC address has not been transferred after the aging timer has been exceeded. The default aging time is 300 seconds (5 minutes) and can be manually modified by command.

Switch#show mac Address-table Aging-time

Global Aging time:300

Vlan Aging Time

----    ----------

Switch (config) #mac address-table aging-time?

<0-0> Enter 0 To disable aging

<10-1000000> Aging time in seconds

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