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Old 02-01-2019, 03:25 PM   #1
Spork Schivago
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Default Questions about VLANs and Cisco Hardware

Does anyone have any experience with Cisco hardware, specifically WLCs, Wireless APs, and VLANs?

I took the CCNA courses, but it was a very long time ago. We didn't go over wireless technologies in the course because back then, I believe wireless was fairly new in the business sector.

To start with, I'm having some trouble understanding VLANs. I realize on Cisco hardware at least that a VLAN ID is layer 2, a VLAN interface is layer 3. I am a bit confused with VLAN tagging though.

I have a setup like this:
Code:
Cisco Router
--------------
Interface GigabitEthernet 0/0/1 <-- access port, Public Static IPv4 address

Interface Wlan-GigabitEthernet0/1/8
 Description: Internal switch interface connecting to the embedded AP
 switchport trunk native vlan 999
 switchport trunk allowed vlan 10,20,40
 switchport mode trunk
end

VLAN ID 10
VLAN ID 20
VLAN ID 40

Interface VLAN 10 <-- Network Address 10.0.0.0 / 24, IP address 10.0.0.1
Interface VLAN 20 <-- Network Address 10.0.20.0 / 24, IP address 10.0.20.1
Interface VLAN 40 <-- Network Address 10.0.40.0 / 24, IP address 10.0.40.1

WLC
-----
Interface management <-- Untagged, IP address 10.0.0.2
Interface vlan_employees <-- Tagged VLAN 20, IP address 10.0.20.2
From the built-in WLC, I have trouble pinging the router. I read the management interface needs to be left untagged. But if it's left untagged, how does it work? The packet leaves the WLC, untagged, enters the WLan-GigabitEthernet 0/1/8 interface, and then gets tagged with VLAN 10? Or does the packet reach the GigabitEthernet 0/1/8 interface, sees that it doesn't belong to a VLAN, and the interface drop the packet?

My understanding about the native VLAN is if the packet coming into the interface is tagged with the same VLAN that is set as the native VLAN, the interface will remove the tag and forward the packet to it's destination, untagged. Is that correct?

Thanks!
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Old 03-04-2019, 08:08 PM   #2
ant3202
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Default Re: Questions about VLANs and Cisco Hardware

im not sure.... but had you tried encapsulation dot1q on the router interface?
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Old 03-12-2019, 11:18 AM   #3
Spork Schivago
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Default Re: Questions about VLANs and Cisco Hardware

I have tried, but I do not think I have done it right. I need a better understanding of VLANs and how the packets look when traveling from various networks to other networks.

For example, what happens and what does it look like if a packet is coming interface 1 on a wireless LAN controller, with an IP of 10.0.0.3, untagged, passing through interface 1 on the router (just as an example) which has IP address of 10.0.0.2? What happens to the packet if it's untagged when it leaves the wireless LAN controller? What happens if on the router, it's a VLAN interface? What happens if it's tagged when it leaves the wireless LAN controller?

I see many tutorials that show how to setup the dot1q on the router's interface, but that command just isn't there for my router. It's a little bit different.
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