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Access、Trunk and Hybrid and this VLAN

Three modes switch port

On the switch,There are three commonly used configuration mode,Respectively Access (Access),Trunk (trunk or trunk) as well as Hybrid (Hybrid),These three interfaces operating mode determines the corresponding interface for processing the attitude data packets on the switch。Nowadays,Routing to elaborate on these three models。


Since the switch has divided the virtual LAN VLAN function is,Therefore, it is allowed to switch into the Ethernet frame data marked with a tag,VLAN is used to identify different data flows,To be forwarded。This is what we often say that this standard 802.1q,It provides,Switch inserted after the source and destination Mac address of the Ethernet frame length is 4 bytes VLAN information,This is the VLAN tag。

Also why,This is inserted through the Ethernet frame is not directly be read directly on our computers and other equipment,Only switches can understand,So,There will be a tag (tagging) and untag (Go to the tab) say。

802.1Q frame is inserted with a 4-byte identification on standard Ethernet frame。Contains:
2Byte protocol identifier (the TPID),Counter current fixed value of 0x8100,Flag information indicates that the frame with the 802.1Q。
2Bytes of Tag Control Information (TCI),It contains three domains。
Priority fields,Accounting 3bits,It indicates the 802.1p priority,Value 0-7,7It is the highest priority,0The lowest priority。The field is employed 802.1p。
Canonical Format Indicator (CFI)area,Accounting for 1bit,0Represent the canonical format,Applied to Ethernet;1It represents a non-canonical format,Used in Token Ring。
VLAN ID field,Accounting for 12bit,For ownership of the marked VLAN。

Native Vlan

On Cisco devices,That name;It was also generally used to call it as the default VLAN,This concept is unique to them Trunk and Hybrid,Because only they are allowed by multiple VLAN,In the Access allows only one VLAN by,Naturally you do not need to care about this issue。

Then,Since it can take forward the label,Why does it need such a role? This concept was first reflected in the Cisco switch,Because Cisco switches itself has a lot of agreement,For example, CDP,of course,There are many other protocols such as stp are marked with a tag does not recognize the Ethernet frame,Otherwise, the VLAN to which the recognition? How to identify? Moreover different switches may be different tag,Although there 802.1q,However, interoperability between devices from different manufacturers will always be a problem with all kinds of weird,So,The native VLAN clever to avoid this problem,Of a specific VLAN tag to send。Now,Almost all of the native VLAN switches have this feature,Equipment interoperability between different vendors,Also to a large extent rely on it to complete。

Native VLAN match in some devices is permitted,This will lead to information disclosure of interoperability between different VLAN mutual;If the native VLAN is set to the user VLAN,Users are also likely to lead to a threat to penetrate the network VLAN。


It can only belong to one VLAN,You can also be understood as it only has a default VLAN,This is what the most common computer interface connection,In the next legend among all,Are transmitted and received with respect to the switch in terms of,Ji Song sent from the switch,Receiving the message is received,Like a router inbound and outbound as,Do not confuse oh。

Process flow when I received the message when Access


When the process flow when the Access Port sends packets



It belongs to VLAN,So the need for the concept of a default VLAN the native VLAN。

Trunk interface when receiving the processing flow when the packet



When the processing flow when transmitting packets Trunk port




It differs in that it is a place Trunk Access can act as a role connected with computers and other equipment,Other,It can be set issues a message to multiple VLAN tags,Not necessarily only the native VLAN can。

Hybrid port when receiving the processing flow when the packet



When the processing flow when transmitting packets Hybrid port



At last,The flowchart and part borrowed fromHereandHere

Original article written by Gerber drop-off:R0uter's Blog » Access、Trunk and Hybrid and this VLAN

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