I noticed this error (or, if you like, discrepancy) while checking the translation on NETGEAR switches. The point 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 a very different technical meaning between them.
Let's deal.
Consider the problem with the following examples:
1 Cisco
2 HP
The attentive reader will notice that "trunk" in these examples has a different meaning.
Let's dig.
Cisco Version
Cisco under "trunk'om" understands point-to-point channel (communication channel directly connecting two devices), which connects the switch to another network device, such as another switch or router. His task is transmit traffic of multiple VLANs through one link and provide them with access to the entire network. Commonly called "trunk", which is logical.
Operating principle
Let's start with what is a VLAN?
VLAN stands for Virtual local area network or virtual local area network. This is a technology that allows you to divide one physical network into several logical ones that work independently of each other. For example, there is an enterprise Human Resources Department, bookkeeping ΠΈ IT department. They have their own switches, which are connected through a central switch into a single network, and the networks of these departments need to be separated from each other. That's when VLAN technology comes to the rescue.
It looks like a network divided into VLANs (virtual networks).
Often different colors are used to designate a VLAN.
So ports marked in green are in one VLAN, and ports marked in red are in another. Then computers that are in the same VLAN can interact only with each other, but with computers that are part of another VLAN, they cannot.
Switching table changes in VLAN
When creating VLANs, another field is added to the switching table for switches, in which VLAN identifiers are indicated. 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 data link layer, data is transmitted in the form of frames (frames). When transmitting frames from one switch to another, information is needed about which VLAN a particular frame belongs to. This information is added to the transmitted frame. Currently, an open standard is used for this purpose. IEEE 802.1Q. Stepwise evolution of a frame in a VLAN
- The computer generates and sends a normal frame (frame, also known as a link layer packet, i.e. switch level)without adding anything. This frame looks like this:
- The switch receives a frame. In accordance with the switching table, he understands from which computer the frame came, and to which VLAN this computer belongs. Then the switch itself adds service information to the frame, the so-called tag. The tag is a field after the sender's MAC address, which contains, roughly speaking, the VLAN number. This is how the frame with the tag looks like:
The switch then sends that frame to the other switch.
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The switch that receives the frame extracts information about the VLAN from it, that is, it understands which computer this frame should be sent to, removes all service information from the frame and transmits it to the recipient computer.
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A frame arrives at the recipient's computer without service information.
Now back to ourtrunk'y'. Switch ports that support VLANs can be divided into two groups:
- Tagged ports (or trunk ports Ρ Cisco)
- Untagged ports (or access ports)
We are interested in tagged ports or trunk ports. They just serve to one port it was possible to transfer data belonging to different VLANs and receive data from multiple VLANs on one port (we remember that usually ports from different VLANs do not see each other).
In this figure, the tagged ports are number 21 ΠΈ 22that connect two switches. Frames will pass through them, for example, from a computer Π to the computer Πthat are in the same VLAN, according to the scheme described above.
So, the communication channel between these ports is Cisco just called "trunk'om".
Version HP
How does the company interpret this term?
Here we are not talking about VLAN at all. In case of HP we're talking about link aggregation technology. They have "trunk" - is logical channel, which combines multiple physical channels. Such a combination allows you to increase the throughput and reliability of the channel. Let's take an example. Let's say 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 connections between switches - then these connections will transfer frames to each other in a circle, i.e. form loop (moreover, broadcast frames will be duplicated over and over again, introducing switches into a broadcast storm).
Such redundant connections are considered redundant, and they need to be eliminated, for this purpose there is the STP (Spanning Tree Protocol). Then, out of our four connections, STP will turn off three because it considers them redundant, and only one connection remains.
So, if we combine these four physical channels, there will be one logical channel with increased bandwidth between the switches (the maximum rate of information transfer over a communication channel per unit of time). That is, four channels are involved at once, and the problem with redundant connections is solved. It is precisely this logical (aggregated) channel that is called HP "trunk'om".
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 link have the same parameters:
- media type (twisted pair, optical fiber, etc.),
- speed,
- flow control and duplex mode.
If one of the ports in an aggregated link fails, the link will continue to function. Ports of an aggregated channel are perceived as a single unit, which corresponds to the idea of ββa logical channel.
And to fully clarify the picture, we note that such a technology Cisco called EtherChannel. EtherChannel is a link aggregation technology developed by Cisco. The meaning is the same, it allows you to combine several physical Ethernet channels into one logical one.
Thus the term trunk translates according to the context as follows:
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in the documentation for the switches Cisco β trunk port, tagged port, trunk port;
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in the documentation for the switches HP β port port, port port.
In case you want to understand the topic in more detail, below is a small list of sources.
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Cisco: (or like this:
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HP:
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VLANs:
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Link Aggregation:
Source: habr.com