Why trunk ports on a switch

This is why i assumed you are already knowing that, just pointing this out in case someone else is reading. Like I said, you got it right just pointing it out that you did it correct!

Because you are sending tagged frames from the router down to Switch6. Otherwise packets. Because if you know how networking works, it's possible to make this work without configuring this as a trunk-port. Additional reuirements: DTP-mode auto or off on all those interfaces.

What will happen then is that it will magically work without any trunk-ports except for the port leading up to the router. It's not complicated, but i think it requires some technical discussion outside the scope of your original one. This is not the recommended best practice way of implementing it since it's really a misconfiguration that is difficult to troubleshoot, but it will work. Simply put, because it doesn't know where to forward the frame. Remember a switch looks at Layer 2 information meaning destination MAC-address to make a forwarding decision.

It will actually receive the tagged frame on a trunk-port, look at it and then find out that it does not have that local VLAN in it's VLAN-database so it will discard the frame. I don't really know what you are asking here. This protocol is not used in production networks due to some design flaws with it - it's very easy to put a misconfigured switch into your already working network and have it ruin the VLAN-database in the entire Switching domain.

Again, this is a question i don't understand - sorry. I tried something different, I created a VTP in both cases. Everything is "flowing smoothly" now! Don't worry about subnets, after hit my head against the wall I finally learned.

Additional requirements: DTP-mode auto or off on all those interfaces. Untagged packets cannot pass through this link..

That will be a problem, right? What would be the case that I have to use or know to use that protocol? Is necessary to encapsulate a Switch Port? It's a little confuse to try explain but, what I'm wanting to speak is that packet doesn't have as destiny the switch.

Hey, Thanks for your great help, and I'm sorry if you cannot understand what I was trying to say. You're welcome. Although i just put it as a "distribution switch" since it's technically aggregating the traffic from Switch 5 and Switch 7 up towards the router. A distribution switch in general attaches to at least one core-switch. Or in smaller networks, they are combined into a single switch.

Yes in the configuration i was talking about the one without a trunk-port on Sw5 and SW7 the uplink was configured as access-ports only. In general you don't need to worry about this, but DTP is a protocl that tries to detect what type of device you attach to your switchport. It's just So the general best practice is, as almost always, to use static configuration like this:.

In either case it's recommended to not use it and if you do, the recommended way is to use "Dynamic Auto" on the access-switch and "dynamic desirable" on the Distribution switch. The reason those requirements exists is because in any other configuration DTP will negotiate the link as a trunk-port and then it's no longer an access-port assigned to a specific VLAN - that would make the configuration without trunk-port not work The protocol was probably designed to overcome cabling issues and related configuration changes needed inside the switch depending on if you connected the switchport to another switch or to an end-host.

So DTP helped with that, just connect a cable and if it's connecting to a switch - a trunk port forms, if it's connected to another device without DTP-frames This is a very complicated process, but it will try to see if the destination-ip address it's trying to reach is located on the same ip-subnet as itself. If it is, then send an arp-broadcast to ask for that host's MAC-address.

With only one host in your subnet, chances are it's going to be in a different ip-subnet. On the local host itself, it will save this information in it's ARP-cache so it doesn't have to use this process again for a while.

I am sure that people are using VTP, however most networks don't use it. There are perfectly valid reasons for it, and the best practice implementation is:. Simply put, because of how it works.

A lab-switch with a higher revision number can destroy a network if you put it inside without reseting the revision number. Even if you are careful with that, the protocol itself is proven over time to be unreliable and difficult to control But just to add - switchport trunk encapsulation dot1q - is only required on a Multilayered switch where IP-routing is enabled.

If it's a layer 2 switch that can't do ip-routing of any sort, then you just need this command:. I mean, If I don't use, for instance, at that topology that I showed, the packets doesn't reach to Layer 3? Anyway, I put in trunk mode just Switch's Interface, and it's works. Actually you should not have to use that command on the switch itself.

The problem i think lies in that ISL is not supported in modern switches, but in the older one where you actually could pick between ISL and On older platforms you need to specify the trunking method - While on newer devices there is only one option, so you don't need this command.

Packet Tracer is limited in such ways that it helps understand some topics but can confuse with others. But in your version of packet tracer they seem like they simulate older platforms wher eyou have to specify ISL or Dot1q.

But i guess you would have to trust me that in the real world you typically won't have to specify that unless you're on very old hardware :! On a multilayered switch, such as a , you would need that command since it also do IP-routing.

On Layer 3, I can specify one encapsulation type Got it? Is my logic flawed and it works for another reason? Switch 6 will tag the frames when sending to R1 out a trunk port.

R1 will return tagged frames and switch 6 untags them. When switch 6 distributes the frames out of access ports, they are untagged and can be received by the end points. The reason this works is because like you say, all links between the switches are connectec over an access-port.

It's then tagged towards the router. Router routes the packet and sends a tagged frame down towards Switch6. Switch6 will then look at this and forward it out all ports that belong to this VLAN. This is a misconfiguration because you are connecting the switches through access-ports. The reason that is considered a misconfiguration is becuase you could have different VLAN's configured on Switch5 and Switch6.

That would mean you have bridged two VLAN's. Which is what typically happens on a live network when this happens, everything will work but you will have broadcast traffic from two different VLANs spreading to eachother.

Thank you for the explanation Daniel! This article will give you the basic knowledge of these two most confusing terms in the cisco world. In very simple words, the trunk of a tree carries water and essential nutrients to all the branches and leaves of a tree.

Similarly, the trunk in VLAN especially carries streams of signals to the correct destination or location. Basically, we can say it is a link that carries many signals simultaneously, which leads to creating more efficient network access between two nodes.

Basically, it is a type of connection on a switch. There are many differences between the trunk port and the access port. Similarly, if any device is plugged into this port, then it will only be able to communicate with other devices that are in the same VLAN. Trunk ports mark frames with some uniquely identifying tags which are either They are used to add VLAN information to frames as they are transported between the switches and other devices.

Sign up. Term of the Day. Best of Techopedia weekly. News and Special Offers occasional. Trunk Port. What Does Trunk Port Mean? Transmission Methods In order to accommodate VLAN trunking, the trunk port routes a data packet that contains a tag in the frame header.

Setups and Structures The versatility of a trunk port and a VLAN trunk can be shown through various data flow charts showing how the VLANs are chained together and use common resources. Share this Term. Tech moves fast! Stay ahead of the curve with Techopedia!

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