How does the translation of the term trunk depend on the vendor of the switches?

How does the translation of the term trunk depend on the vendor of the switches?

I noticed this error (or, if you like, a discrepancy) during the translation check on the NETGEAR switches. The fact is that when translating the term “trunk” , it is necessary to take into account whose interpretation the vendor adheres to Cisco or HP , because there is very different between them technical sense.

Let's figure it out.

Consider the problem in the following examples:

1. Cisco

2. HP

The attentive reader will notice that “trunk” in these examples has a different meaning.

We will dig.

Cisco Version

Cisco by “ trunk “ om ”means point-to-point channel (a communication channel directly connecting two devices ) , which connects a switch and another network device, such as another switch or router. Its task is to transfer the traffic of several VLANs through one channel and provide them access to the entire network . In common people it is called "trunk" , which is logical.

principle of operation

Let's start with what is a VLAN?

VLAN stands for Virtual local area network or VLAN. It is a technology that allows you to divide one physical network into several logical, operating independently of each other. For example, there is a personnel department , accounting department , and IT department . They have their own switches, which are connected through a central switch into a single network, and now the networks of these departments need to be separated from each other. That's when VLAN technology comes to the rescue.

This is how the network is divided into VLANs (virtual networks).

Often, different colors are used to designate a VLAN.

So the ports marked in green are in one VLAN, and the ports in red are in the other. Then computers that are in the same VLAN’e can only communicate with each other , but cannot interact with computers belonging to another VLAN.

Changes in the VLAN switching table

When creating VLANs, another field is added to the switching table at the switches, which specifies the VLAN IDs. Simplified it looks like this:

Here we see that ports 1 and 2 belong to VLAN 2 and ports 3 and 4 belong to VLAN 10.

Go ahead. At the link level, data is transmitted as frames ( frames ). When transferring frames from one switch to another, information is needed on which VLAN the frame belongs to. This information is added to the transmitted frame. At this time, the open standard IEEE 802.1Q is used for this purpose. Step-by-step frame evolution in VLAN

  1. A computer generates and sends a regular frame (a frame, also known as a link layer packet, that is, a switch layer) , without adding anything. This frame looks like this:

  1. Switch receives frame. In accordance with the switching table, he understands from which computer the frame came, and to which VLAN the computer belongs. Then the switch itself adds service information to the frame, the so-called tag. The tag is the field after the sender's MAC address, which contains, roughly speaking, the VLAN number. This is the frame with the tag:

The switch then sends this frame to another switch.

  1. The switch that receives the frame, extracts the VLAN information from it, that is, understands which computer to transfer this frame to, removes all the service information from the frame and sends it to the recipient's computer.

  2. A frame comes to the recipient’s computer without the service information.

Now back to our “ trunk ’ y ”. Switch ports that support VLANs can be divided into two groups:

  1. Tagged ports (or trunk ports of Cisco )
  2. Untagged ports (or access ports )

We are interested in tagged ports or trunk ports. They serve to ensure that through one port you can transmit data belonging to different VLANs and receive data from several VLANs to one port (we remember that usually ports from different VLANs do not see each other) .

In this figure, the port numbers 21 and 22 are tagged, which connect the two switches. Frames will pass through them, for example, from computer E to computer A , which are located in one VLAN, according to the scheme described above.

So, the communication channel between these ports is called trunk ’th” by Cisco .

Version HP

How do companies interpret this term?

Here, in general, we are not talking about VLANs. In the case of HP , we are talking about channel aggregation technology. They have a “trunk” - this is the logical channel , which combines several physical channels . Such a combination allows to increase the capacity and reliability of the channel. Let us consider an example. Suppose we have two switches, each of which has four ports and these ports are interconnected by four wires.

If you leave everything as it is - just the connections between the switches - then these connections will transmit frames to each other in a circle, i.e. form loops (and broadcast frames will be duplicated by introducing switches into a broadcast storm) .

Such duplicate connections are considered redundant and must be eliminated; for this purpose, the Spanning Tree Protocol (STP) exists. Then out of our four connections, STP will turn off three, because it considers them redundant, and only one connection will remain.

So, in the case, if we combine these four physical channels, there will be one logical channel with increased bandwidth between the switches ( maximum information transfer rate over a communication channel per time unit ). That is, four channels are involved at once, and the problem with redundant connections has been resolved. It is this logical (aggregated) channel that is called by HP trunk ’ ohm ”.

Link aggregation can be configured between two switches, a switch and a router. Up to eight physical channels can be combined into one logical channel. It is important that all ports that are combined into an aggregated channel have the same parameters:

  • media type (twisted pair, fiber, etc.) ,
  • speed,
  • flow control and duplex mode.

If one of the ports in the aggregated link fails, the link will continue to work. Ports of the aggregated channel are perceived as a whole, which corresponds to the idea of ​​a logical channel.

And to completely clarify the picture, we note that this technology is Cisco called EtherChannel . EtherChannel is a channel aggregation technology developed by Cisco . The meaning is the same, it allows you to combine several physical Ethernet channels into one logical channel.

Thus, the term trunk is translated depending on the context as follows:

Source text: How does the translation of the term trunk depend on the vendor of the switches?