Ethernet protocol
The concept of the gateway
Provides a door for LAN users to fly through the door, you can access to another network. This door is called the gateway.
Each router interface represents a different network
Ethernet
Traditional Ethernet
1. The maximum transmission distance is limited only 100m, exceeds the distance signal becomes weak, to solve this problem, the use of Hub (concentrator (Hub is the wireless AP))
The role of hubs? (Sub)
1. The signal amplification
2. The data is received from an interface, parts of N copies, transmitted from all other interfaces
3. The half-duplex (at the same time, can accept or transmit data)
As the half-duplex hub of the working mechanism, the network will create a conflict, the scope of the conflict involved is called the collision domain
DIX Ethernet protocol (data link layer)
DIX1.0
Network speed .5 / Mbps
CSMA / CD
CS: Carrier Sense
MA: Multiple Access
CD: collision detection
Collision Detection Carrier Sense Multiple Access technology, to solve the conflict
Using this technology, Ethernet, DIX2.0 10Mbps
Speed, high efficiency, low cost, stability
Simple works
Starting first listen
Edge hair while listening
Conflict suspended
Random wait
The new issue of network congestion
Single occupancy network, causing other people are in a wait state, thereby causing network congestion
sub (not smart)
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bridge bridge (smart) due to the pure software implementation of the bridge, causing no way to use more interfaces
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Data transfer switch switch (smart) implemented in hardware
switch
Smart Switch reasons:
It can learn the source MAC address of the Ethernet data frame, the MAC address table recorded inside. MAC address table records the MAC address of the interface from which to learn.
Switch data frame three ways:
1. Forward: After receiving a data frame, found the destination MAC address exists my MAC address table, it will forward the data
2. Flooding:
1. When you receive a data, we found the destination MAC address does not exist in my MAC address table, it will flood (mass) of this data, if (destination MAC address) and the other end receives the data, it will return a data, the switch will learn, recorded
2. receive a broadcast data will flood (to stop routing)
3. discarded
1. receive an error data frame will discard the
2. If the switch receives a data from one interface but also immediately sent out from the interface, it will discard the data (because it knows, this interface below a sub, and data exchange has been completed)
Ethernet data frame integral structure
MAC address is represented in hexadecimal
6Byte，48bit
The preamble
Distinguished from frame to frame
The destination address (destination MAC address)
Determines that the data frame is a unicast or multicast, if the MAC address, the eighth bit is 0, then this is a unicast MAC address, if the 8th bit is 1, then it is a multicast MAC address If all of the MAC address is 1, then the MAC address is the broadcast MAC address. 1, if not all, then it is a multicast MAC address
Source address (source MAC address)
Type (type)
Data (data)
CRC
Determining whether a frame is damaged