Shulou(Shulou.com)06/03 Report--

1. Introduction: Ttunk is generally translated as "trunk line, trunk line, long-distance line" in network terms, but it is generally used in English without translation. In routed / switched networks, Ttunk is often referred to as "relay (transparent transmission)". In voice-level application lines, Ttunk generally refers to the "backbone network, telephone trunk", that is, the connection circuit or channel between two exchanges or exchanges, which transfers between the devices at both ends and serves as the transmission link for signaling and terminal equipment data.

Second, function: to enable the same VLAN to communicate across the switch.

3. Communication process:

There are two modes for switched ports: access and trunk. The connection terminal (such as PC) uses access mode, and the device-level connection uses trunk mode. Add the access port to a VLAN, then the port will only forward the data from this VLAN to the PC,PC. After passing through this port, the ID of the VLAN will be typed and forwarded to the same VLAN.

4. VLAN logo:

Currently, the most commonly used VLAN identity is IEEE 802.1q, which uses an internal tagging mechanism. The relay device inserts a 4-byte tag into the data frame and recalculates the frame check sequence.

Fifth, the format of IEEE 802.1q frame:

(1) the 2-byte marking protocol identifier (TPID) contains a fixed value of 0x8100, which indicates that the frame has 802.1q tagging information.

(2) the 2-byte tag control information (TCI) contains the following elements.

1) 3-digit user priority (Priority): 802.1g does not use this field

2) 1-bit canonical format identifier (CFI): CFI is commonly used in Ethernet and token ring networks. In Ethernet, the CFI value is usually set to 0

3) 12-bit VLAN identifier (VLAN ID): this field uniquely identifies the VLAN to which the frame belongs. VLAN ID can uniquely identify 4096 VLAN, but VLAN 0 and VLAN 4095 are reserved.

6. Configuration steps and commands of Trunk:

Note: Native VLAN is the native VLAN. It can be unmarked, but there can be only one VLAN, which is VLAN 1 by default, or it can be changed to another VLAN.

7. Other configurations of Trunk:

Layer 8, layer 3 switching: because Trunk can not achieve communication between different VLAN, it needs to be achieved through layer 3 devices (routing / layer 3 switch), so there is a layer 3 switch.

9. Traditional MLS (Multi-layer switching): the three-tier engine processes the first packet and then transfers the information to the second layer for further processing, which is an old-fashioned structure.

10. MLS based on CEF (Cisco Express forwarding): forwarding by viewing the forwarding information base and the adjacency table is much faster than the traditional one.

The forwarding process of layer 3 switch:

1. Four interfaces of the switch belong to VLAN 10 and the other four interfaces belong to VLAN 20. If the switch has been configured with the virtual interfaces of the two VLAN, it is like virtualizing the gateways of the two VLAN inside the switch. When the data comes in from the physical interface that belongs to VLAN 10, it maps to the virtual interface of VLAN 10 to find its own gateway.

2. If the interface of the switch belongs to Trunk mode, then the interface belongs to all VLAN. The switch looks at the label in the data frame and determines which virtual interface it should "forward" to.

Configuration of layer 12 and layer 3 switches:

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