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1 Rookie

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26 Posts

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December 18th, 2020 09:00

Port behavior and Vlan

We have multiple vlans on our switch closets. Our core switch is a N4064F. All of our switch closets come into the core switch. The switch closet ports to core are set to trunk on VLan1. The ports they connect to on the core are set to Access and VLAN1. My question is how does this work? If packets on the switch closet are tagged with another VLan, are they encapsulated going out the trunk port as VLan1 then continue on their way to their appropriate VLan in the core? Looking at the manual, any packets with a Vlan tag other than that of the access port they come in on are dropped. 

4 Operator

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2.9K Posts

December 29th, 2020 07:00

Right, the LAG settings override the individual port settings.

4 Operator

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2.9K Posts

December 18th, 2020 15:00

Hello,

 

Could you help me understand your question? Generally speaking, physical ports are trunked, not VLANs. Regarding your question about VLANs, the communication will be based on the matched configuration. 

If it's originating from VLAN 1 untagged on the core, it will be sent to the untagged VLAN of the connected switch(would be 1 by default if set in trunk mode).

 

Assuming that both switches are set in trunk mode on the ports connecting them, and you have a traffic originating from VLAN 5 on the core it will be sent out tagged if using the port connecting the 2 switches and received as tagged VLAN 5 on the connected switch (just using VLAN 5 as an example).

 

Please let me know if this helps.

1 Rookie

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26 Posts

December 22nd, 2020 07:00

I guess my confusion is where the trunk is forwarding all Vlan traffic to an access port which only accepts a single Vlan. Does the trunk port "encapsulate"(for lack of a better word) the the forwarded packets and the access port simply see them as from Vlan1?

4 Operator

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2.9K Posts

December 22nd, 2020 14:00

PG 766 gets into VLAN tagging: https://dell.to/3hdkD8Z

 

By default the trunk ports should carry all VLANs, so it should send the traffic to the right place, however it can be set so that the trunk port only carries specific VLANs, and if it is not in the list it will drop the traffic. Another possibility may be in configuration expectation. I say this because our switches don't have a default allow policy for VLANs (I think Cisco does, if I'm not mistaken). You would need to allow  them with ACL configuration for your other ports. 
 
If that's no helpful, you're also welcome to share the running configuration. That may help clarify specifics.

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December 28th, 2020 13:00

I may have figured this out, hopefully. The access ports on the core switches are set as part of a LAG and that LAG is set to trunk. Can you tell me what the expected behavior is here? If a port is set to "Access", but is a member of a LAG and that LAG is set to trunk, will the port in effect be a trunk?

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