Data Link Layer Basics
Data Name: Data frame (Frame)
function:
to establish a logical link, maintenance and demolition
frame packaging, transport, synchronization
error checking frame
flow control
Ethernet (ethernet):
LAN: Ethernet work the data link layer
topology:
bus, star, tree, integrated
Build three problems:
data conflicts: CSMA / CD collision detection band carrier sense multiple access
data communication: MAC address of
data interpretation: the same frame format: Ethernet Ⅱ; IEEE802.3
CSMA / CD :( to drive an example) 
the MAC address: Ethernet network identifier used to identify an individual device or group of devices
represented by 12 hexadecimal representation before 6 (IEEE allocated) for the factory, after 6 represents a (discretionary manufacturer) for a device
of 48 bit, 6 bytes represented; the last bit of the first byte of the destination MAC address is a unicast address is 0, the multicast address is always 1, 48 bits are a broadcast address (multicast address and wherein the broadcast address is a logical address)
frame format 
range frame format length: 64-1518 byte
length: table data immediately following the data length of its resumed
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Sublayer of the data link layer:
http://m.elecfans.com/article/647662.html
medium access control (MAC) sub-layer
logical link control (LLC) sublayer
switch (formerly bridges) works
switches to create LAN major equipment
can forward the data to the destination address in the Ethernet frame intelligent; segmented collision domains, full duplex operation
Huawei switches series:
the S2700: Fast Layer Interface
S5700: Gigabit downlink interfaces, Gigabit uplink interface
S12700: campus
CE12800: Data Center
Switch-level division: access layer; convergence layer; core layer
Forwarding principle switch: (MAC address table): learning the source MAC address only
acquaintance state: a blank
MAC address learning: the received data frame to view the source address (no record) to do the recording, mapping mac address and port; in view the destination address (MAC address table Comparative) no
broadcast unknown data frame:
recipient response: compare their client mac address, is inconsistent, discarding data; consistent reply; switch to learn the destination MAC address of the
switch forwarding unicast unicast communication data :
update the MAC address: aging time of 300 seconds
冲突域与广播域
单工，半双工，全双工
单工：信道单一，通信方向单一（BB机）
半双工：信道单一，同一时间通信方向单一（对讲机）
全双工：双信道，同时可以双向通信（电话）
冲突域
多个网络节点的通信使用同一主线，同一时间只能一个节点进行数据传输，如果多个节点同时发送数据，会产生冲突，这个区域叫做冲突域
广播域
指接收同样广播信息的节点的集合；
交换机分割冲突域，但是不能分割广播域
交换机内部转发方式
存储转发：应用最广发；对
快速转发：延迟小速度快；不能提供错误检测；没有缓存，不能将不同速率不同
分段过滤:检查数据包的长度是否够64字节；不提供数据校验
交换机的配置
查看MAC地址表：
See the switch MAC address
Display bridge (Bridge) mac-address 
to view information about the adjacent switch
Lldp enable startup protocol (Link Layer Discovery Protocol (Link Layer Discovery Protocol, LLDP) is a data link layer protocol, network device may advertise itself to other devices by sending status LLDPDU (Link Layer discovery protocol Data Unit ) in a local network. enables a network device discovery protocol state and inform each other, mutual information.)
Display LLDP neighbor (neighboring) brief (simple, concise)
on-mode (full-duplex, half duplex, speed) port; the default is auto-negotiation, auto-negotiation must first shut down before changing
Undo negotiation (negotiation) Auto
Duplex: change the mode
Speed: band the rate of
open remote management services:
to configure the IP address of the switch
to configure virtual IP
Interface vlanif 1
IP address xxxx 24-
Undo the shutdown