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General Switchport untagged traffic question
Greetings,
I am currently getting ready for the DCAN-100 exam while using the study guide as a roadmap for my preparation. Unfortunately, all my practical usage of Dell switches, for now, comes from demos in Dell’s Demo Center and observations of my seniors while in production… I don’t think my company’s clients or my company would approve experimentation, much to my dismay :Smile:
So, I stumbled upon this chasm called general switchport mode, trying to find how to properly understand reading and configuring it. I will further explain what I am stuck upon…
My scenario is having two switches of the N series connected via a general link which has two untagged Vlans. For example, 1 and 2. The PVID I have put as configuration is PVID 2.
Also I have 2 PCs belonging to the same subnet (let’s say their IPs: 10.1.1.1/24 and 10.1.1.2/24) each one connected to its respective switch via the cli commands:
switchport mode access
switchport access vlan 1
and the general switchport mode has smt like the following as configuration
PVID:2
Untagged vlans:1,2
And the theory is:
Untagged traffic that enters the switch through this port is tagged with the PVID. The PVID assignment must be to an existing VLAN.
So… My questions are…
What is the dominant untagged ingress traffic’s vlan as concerns the general switchport configuration? 1 or 2 (or something else if I have more than two untagged Vlans, I mean, is it depending upon the access port configuration?)? Is the answer 2 cause of the PVID? Is the PVID only used between the switches and then changes to vlan 1( in this case) again? … Needless to say that I find the whole “more than one untagged vlan” a bit…. Disorienting…
Also while reading this was always pop ups:
While untagged traffic may be sent via several untagged VLANs, returning untagged traffic will only be received by the PVID and therefore will NOT be forwarded to a specific VLAN.
Can you please clarify what the returning untagged traffic means?
Thank you in advance and for you time…
(also please forgive any spelling and/or grammatical errors I am not a native English speaker.)
P.S Also, is there a Dell portal/site unknown to me that I can go and make small labs like this?
Anonymous
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June 20th, 2018 10:00
Without the PVID, an interface will not be able to receive untagged packets.
As an example, we will look at connecting a General mode interface to another General mode interface using the following config:
console(config-if)# switchport mode general
console(config-if)# switchport general allowed vlan add 2,3,4 tagged
console(config-if)# switchport general allowed vlan add 5,6,7 untagged
console(config-if)# switchport general pvid 1
With this configuration, the interface will forward and received tagged packets for VLANs 2,3,4. Traffic originating from VLANs 1,5,6,7, will be forwarded out the interface as untagged packets. When the other interface receives these untagged packets, it will place all this untagged traffic in the PVID, which is VLAN 1. I threw together this little picture to try and give a visual representation of the traffic. Let me know if this helps or not.
Anonymous
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June 19th, 2018 08:00
Here is a great KB article that details General mode: https://dell.to/2t8ONmh
Let me know what questions the KB article does not help clear up.
I am not aware of any lab/virtual application for the N-series switches.
antvas
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June 20th, 2018 00:00
The following are the two reasons for my angst.
So if there are more than one untagged vlans specified why/when is the PVID needed? Or is it needed when there aren't any configured as untagged vlans?
Can you please present me an example of what it means as a "returning untagged traffic"?
Thank you for your time.
antvas
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June 20th, 2018 23:00
Thank you,
This helped a lot and you made it really simple to grasp.
Thank you very much for your time!