Describe the TRUNK function of the core switch

An important indicator is often mentioned in the performance parameters of core switches: TRUNK. Many L2 switches can better solve the conflicts between cost and performance when introducing their performance, the following is a study.

What application advantages can TRUNK be used in core switches? How to configure the TRUNK in a specific core switch product is also discussed in the following article.

The TRUNK configuration function of the core switch is very important. At the same time, the TRUNK can be reasonably configured to provide better transmission performance between the interconnected switches. What is TRUNK? What application advantages can TRUNK bring to us? How to configure the TRUNK in a specific core switch product? Let's take a look at these knowledge.

An important indicator is often mentioned in the performance parameters of core switches: TRUNK. Many L2 Switch products will mention support for TRUNK when introducing its performance, this can provide better Transmission Performance Between Interconnected switches.

1. What is TRUNK?

TRUNK indicates port aggregation, that is, by configuring the software settings, combine two or more physical ports into one logical path to increase the bandwidth between the vswitch and the network node, and merge the bandwidth of these ports, the port is provided with a high bandwidth that is several times the exclusive bandwidth of the Independent Port.

Trunk is a encapsulation technology. It is a point-to-point link. both ends of the link can be a switch, a switch, a router, or a host, a core switch, or a router. Based on the port aggregation (Trunk) function, allows a vswitch and vswitch, vswitch and vro, and host and vswitch or vro to communicate with each other through two or more ports simultaneously to provide higher bandwidth and higher throughput, greatly providing the overall network capability.

Generally, when TRUNK is not used, we all know that this transmission medium feature of the 10/100 M Ethernet twisted pair determines that the bandwidth of the two common 100 switches is only M, if the full duplex mode is used, the maximum bandwidth for transmission can reach 200 MB, which forms a network trunk and server bottleneck.

To achieve a higher data transmission rate, you need to change the transmission media, use a gigabit optical fiber or upgrade to a Gigabit Ethernet, although the bandwidth can reach a Gigabit, however, the cost is very expensive (or even switches need to be replaced), which is not suitable for low-cost SMEs and schools. If the TRUNK technology is used, four ports are bundled together to achieve mbps bandwidth, which can better solve the contradiction between cost and performance.

II. Specific Application of TRUNK

TRUNK (Port aggregation) is a relatively economical method to increase bandwidth between the core switch and network equipment, such as servers, routers, workstations, or other core switches. This method of increasing bandwidth is effective when the connection between a single switch and a node cannot meet the load.

The main function of TRUNK is to bind multiple physical ports (generally 2-8) to a logical channel to make it work like a channel. Bundling multiple physical links not only increases the bandwidth of the entire network.

In addition, data can also be transmitted through multiple bound physical links at the same time, with Link redundancy. When one or more links are disconnected due to network faults or other causes, the remaining links can work. However, in VLAN data transmission, different manufacturers use different technologies.

For example, Cisco products use its vlan trunk technology. Most of the products of other vendors support the 802.1q protocol with the TAG header. In this way, a small giant frame is generated and must be identified using the same port protocol, because the size of a giant frame exceeds the 1518-byte limit of the standard ethereum frame, the common Nic cannot recognize the frame, and the core switch must be de-tagged. The TRUNK function is suitable for the following applications:

1. The TRUNK function is used to connect to the server and provide the server with an exclusive high bandwidth.

2. The TRUNK function is used for cascade between core switches. By sacrificing the number of ports, it provides bundled high bandwidth for data exchange between core switches, improving network speed and breaking through network bottlenecks, this greatly improves network performance.

3. Trunk can provide load balancing capabilities and system fault tolerance. Because Trunk balances the traffic of each core switch port and server interface in real time, once a port fails, it will automatically remove the faulty port from the Trunk group, in this way, the traffic of each Trunk port is re-allocated to implement system fault tolerance.

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3. How to Set TRUNK

To set the TRUNK, you must specify a port as the Trunk, for example, 2/24. To set a port to the TRUNK mode, run the following command: set trunk mod/port [on | off | desirable | auto | nonegotiate] [vlan_range] [isl | dot1q dot10 | lane | negotiate].

The command can be divided into four parts: mod/port: Specify the port to which the user wants to run Trunk; the running mode of the Trunk, including on | off | desirable | auto | nonegotiate. To automatically identify the Trunk over fast Ethernet and Gigabit Ethernet, you must ensure that the Trunk is in the same VTP domain. You can also use the On or Nonegotiate mode to force a Trunk On a port, regardless of whether it is in the same VTP domain.

VLAN range. The default value is 1 ~ 1005, which can be modified, but must have the TRUNK protocol. When TRUNK is used, the protocol on the adjacent ports must be consistent. In addition, you need to set the port connected to the following core switch to TRUNK on the central switch, so that multiple VLANs in the following core switch can communicate with the central switch through one link.

Iv. Precautions for TRUNK Configuration

In a TRUNK, data is always from a specific source point to a destination point, and a single link is designed to process broadcast packets or uncertain packets. When configuring TRUNK, you must follow the following rules:

1: correctly select the number of TRUNK ports, which must be 2, 4 or 8.

2: the ports in the same group must be used. The ports on the core switch are divided into several groups. All ports of the TRUNK must come from the same group.

3: Use Continuous ports. The ports on the TRUNK must be continuous. For example, you can combine ports, 6, and 7 into a port aggregation.

4: generate only one TRUNK in a group of ports.