Ethernet Overview
First, the Ethernet standard
1,10GE Mb / s Gigabit Ethernet 802.3ae
2,1000Mb / S Gigabit Ethernet 802.3z / ab &
. 3, Fast Ethernet 802.3u
. 4, the standard 802.3 Ethernet
II Ethernet evolutionary
shared Ethernet
1, the working principle of shared Ethernet
CS: carrier Sense
of the links before sending data monitoring, to ensure that the link is idle, reduce conflict.
MA: multiple access
data transmitted by each station, multiple stations can be received simultaneously.
CD: collision detection
side edge hair testing, found the conflict to stop, then continue to transmit after a delay of a random time.
Collision detection principle:
Since the two sites at the same time signaling, after superposition, the voltage on the line will swing more than double the normal value, to judge whether the conflict.
2, shared duplex mode: half
3, shared Ethernet speed: 10m / S
. 4, shared Ethernet disadvantages:
broadcast flooding causes: multiple access
poor security reasons: in the physical layer working Hub
low rate, cause of serious conflict: half duplex mode, at any time data from only one direction to the other
switched Ethernet
1, the working principle of switched Ethernet
forwarding table according to the MAC address 
MAC address table: source MAC address learning, destination MAC address forwarding.
If the destination MAC a single wave, then looks up the MAC address table, if the MAC address table has a MAC address forwarding, if the MAC address is not the MAC address, the link flooding.
If the destination MAC is a broadcast on the link flooding.
aging mechanism to maintain MAC address table use.
2, MAC forwarding table
Switched Ethernet to solve the problem:
1, to ease the problem of poor security, the MAC address table screening, works at the data link layer.
2, full-duplex mode of operation to solve the differential rate of serious conflict.
3, disadvantages:
poor security
broadcast flooding
VLAN
1, role: vlan divide broadcast domains, isolation collision domain.
2, the format: 
2B 12 'bit 1bit 3bit
CFI 0 ordinary Ethernet
CFI is a Token Ring Ethernet
Tag power of the number 2 12 0 4096 to 4095 can use
3, vlan in the frame structure: 
of Vlan Standard 802.1 Q
4, Implementation Methods of Vlan create priority order
based on policy-based protocol based on subnet MAC (based on port now we use) based on port
5, port type
Accress port: in (entering direction) to untag marked with labels. Out (transmission direction) out of the frame and allow only the port untag the same frame by pvid.
It is generally used to connect between the host and switch
Trunk Port: in (entering direction) to tag the untag. Out (transmission direction) may not be through out by specific ports is allowed to see through the vlan. Vlan allows multiple tags by, and if the tag vlan port pvid same label is removed.
The connection between the general user switches and switch
Hybrid port:
PVID is only responsible for tagging.
Hybrid There are two tables: tag + untag = allow pass
Out from the tag table is tagged.
Untag out from the table that there is no label.
6, VLAN shortcomings
1, communication can not be achieved in different network segments
2, the number of labels is limited
solution:
1, the route-arm: sub interface configuration in a gateway router's IP address, and play on the label, the use of this host ip address.
2, three vlan: Configuring Layer vlan, vlanif mouth open, configure the IP address.
3, a limited number of tags, used to resolve QinQ technique qinq comprising: a substantially flexible QinQ QinQ (double labels, inner label, outer label)