Remember that if you issue this command:. It will list that all VLAN's are allowed to cross the trunk. Since a VLAN is a logically separated broadcast domain, it will see that it has a trunk-port where this VLAN is allowed to cross and then forward this frame to those switchports.
If it was a unicast, it would just check the mac-address table and forward it out the correct trunk-port which would most likely be the one facing the router. So a clarification from my initial post - it's not a requirement to have all the VLAN's configured locally on the switch when deploying a "router-on-a-stick configuration" like in your first topology.
I kinda jumped ahead with the thinking in my head and i was thinking distribution switch But any switch would still drop the frame if it receives a tagged frame on a trunk-port and it doesn't have any place to go. And when it can't be flooded any further, it will be dropped if that same VLAN is not locally configured on the switch that received it.
I just removed vlan 3 and 4 on SWCnt and ping from And on show int trunk does not show vlans 3 and 4. I mean it does show vlans allowed on show int trunk vlans allowed on trunk Although what i said above is true, I intentionally left out some important piece information for learning purposes. This kind of practice is better rather than setting dtp on switch that are connected each other?
Setting them on access mode and only added specific vlan to pass? The recommended and best practice is to use a trunk-port to connect switches together. The above configuration should not be used in production networks because it's difficult to troubleshoot. And it's very easy to eventually make a mistake causing a "broadcast storm" by bridging two different VLAN's.
For example, you can't make it work for all the VLAN's across all the switches using only access-ports and a single cable.
The trunk port can carry multiple VLAN's over a single port. The access port can only belong to one VLAN and doesn't read That make sense now. If needed to add another vlan on the left switch another cable needs to plug to the center switch since the first cable that is plug in to the center can only carry vlan2 and 3 allowed on the center switch.
So was my first configuration was right or I should kept it dynamic auto on left switch and trunk on center, I think by default it is set to auto? I can't remember needed to look on the books on that. Then if you take the theory you learn to pass your exam into the real world - i will say But if the network does and operate what you want it to do - then it's working, right?
You create a design requirement, then implement a configuration based on the design requirements. For new switches I would pick "auto" as the default, for older switches "i would pick Dynamic Desirable". And if you were to follow best practice recommendation. Assuming the Center switch is a distribution switch but I wouldn't call it that, since it connects end-hosts - then keep the Left and the Right switch in Auto and put the center switch in Trunk.
The command " switchport nonegotiate " is required to completely disable DTP on the port. That is important since that is the best practice implementation of a trunk-port. Always disable DTP, trunk manually. But that is just the general best practice. I've seen networks that uses DTP to help field engineers deploy access-switches easily. So then the field engineers would just have to deploy a switch in the rack, connect a cable that links to the distribution layer switch and it would automagically become a trunk and allow all the VLANs.
Should they miscable it and connect it to another access-switch, hopefully other security mechanisms protects against that but it would not form a trunk where it's not supposed to trunk. Like access-switch to access-switch, access-switch to servers, access-switch to end-hosts etc.
Best practices are more if you want to learn how it's the best and recommended way of implementing things - there will always be deviations from those. Appreciate your input. I will be starting icnd2 study and probably will learn those dtp more as I go through my journey to ccna. It sucks our barnes and noble does not have it stock so I will have to order it online oh well I will just wait. I don't mean to get this thread turn in aside of other topics.
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Understanding Trunk Port. I'm having some problems to understand Trunk Port. I created a topology: Router1 has three Subinterfaces, encapsulated with dot1Q. Best Regards, Thiago. PC 8 - They will also send DTP signals that attempt to initiate a trunk with the other side. This will form a trunk with other ports in the states on , auto , or desirable that are running DTP. A port that is in on mode always tags frames sent out the port.
These links would like to become trunk links and will send DTP signals that attempt to initiate a trunk. They will only become trunk links if the other side responds to the DTP signal. This is the default mode for the running Supervisor IOS. These links will only become trunk links if they receive a DTP signal from a link that is already trunking or desires to trunk.
This will only form a trunk with other ports in the states on or desirable. This is the default mode for COS switches. Sets trunking on and disables DTP. These will only become trunks with ports in on or nonegotiate mode. This option sets trunking and DTP capabilities off.
This is the recommended setting for any access port because it will prevent any dynamic establishments of trunk links. If you turn trunking on for one of these devices, it will not negotiate with the other end of the link and requires that the other link be configured to on or nonegotiate. The other option when choosing a trunk link is the encapsulation method. You can change from the default with the switchport trunk encapsulation command. This method signals between the trunked ports to choose an encapsulation method.
ISL is preferred over The negotiate option is valid for auto or desirable trunking modes only. If you choose on as the mode or if you want to force a particular method or if the other side of the trunk cannot negotiate the trunking type, you must choose the option isl or dot1Q to specify the encapsulation method.
Not all switches allow you to negotiate a trunk encapsulation setting. The XL and XL trunks default to isl and you must use the switchport trunk encapsulation command to change the encapsulation type. The and some switches support only For switches running Remember that the native VLAN must match on both sides of the trunk link for By default a trunk link carries all the VLANs that exist on the switch. You can elect to selectively remove and add VLANs from a trunk link.
To specify which VLANs are to be added or removed from a trunk link, use the following commands. After configuring a port for trunking, use one of the following commands to verify the VLAN port assignments:. The core is configured for autotrunking mode and encapsulation negotiate.
The trunk connected between the access switch is configured to only trunk for VLANs 5, 8, and I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time. Pearson Education, Inc. These unique identifying tags are either However, it's possible for engineers to manually calibrate the setups differently, where they can stop traffic from to and from an individual VLAN.
An Ethernet interface can either function as a trunk port or as an access port, but not both at the same time. 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.
In some ways, this hearkens back to the days of the hardware network topology, where individual pieces of hardware were connected in designated topologies or structures including a bus topology, a star topology, a ring topology or other discrete setups.
By: Justin Stoltzfus Contributor, Reviewer. By: Satish Balakrishnan. Dictionary Dictionary Term of the Day. High-Performance Cloud Computing.
Techopedia Terms. You can optimize performance on access ports that are connected to end stations by simultaneously setting that port as an access port. An access host port handles the Spanning Tree Protocol STP like an edge port and immediately moves to the forwarding state without passing through the blocking and learning states. Configuring an interface as an access host port also disables port channeling on that interface. Ensure that you are configuring the correct interface to an interface that is an end station.
To configure an access host port, perform this task:. Sets the interface to be an access host port, which immediately moves to the spanning tree forwarding state and disables port channeling on this interface.
Note Apply this command only to end stations. Sets the interface as an Ethernet trunk port. By default, a trunk interface can carry traffic for all VLANs. To specify that only certain VLANs are allowed on the specified trunk, use the switchport trunk allowed vlan command.
To configure native VLAN for a Sets the native VLAN for the Valid values are from 1 to , except those VLANs reserved for internal use. The default value is VLAN1.
Before you configure the allowed VLANs for the specified trunk ports, ensure that you are configuring the correct interfaces and that the interfaces are trunks. To configure the allowed VLAN for a trunk port, perform this task:. Sets allowed VLANs for the trunk interface.
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