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VLAN Tagging - Packet Assocation

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#1 matthew_hex


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Posted 17 November 2015 - 06:42 AM



I have a question about VLAN tagging


I have configured 3 VLAN's on a  Dreytek Vigor 2860 router with the following tags. (I do not need support on this router specifically but thought i would mention the model.)


We are using switches that support the IEEE 802.1Q Standard which i understand we need for VLAN tag support.


10  (Data for staff - accessing from computers on ethernet and wireless)

20  (Data for public (not staff) - wireless connections only)

30  (Voice - VOIP)


I have also configured the default gateways and ip ranges for each VLAN


10 - 192.168.10.X

20 - 192.168.20.X

30 - 192.168.30.X


How does the router know which VLAN should be used for allocating an IP to a device. For a computer and Mitel phone for example. I am aware that with the exception of hypervisors, other devices such as computers, laptops and phones, are not VLAN aware. I have read about the TPID -TAG Protocol Identifier  and the first 4 bytes are made of the VLAN TAG, however do not understand how the packets are identified for VLAN allocation unless the packet is marked or identified based other characteristics.

In other words i just want to understand how packets are distinguished and subsequently marked with a specific VLAN tag.

For example

Staff connecting via ethernet and WIFI on a STAFF SSID
Residents connecting via WIFI on Residents SSID
VOIP phones


Kind regards



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#2 technonymous


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Posted 24 November 2015 - 08:55 PM

The packets get tagged after you setup a port to trunk mode. The trunk links will add/remove those tags. It sounds like you want each switch to be all one vlan. So after you assign all ports to the vlan you need one port for trunk. I imagine you would need a Core switch to tie all the switches and trunks together. The router too can be setup to encapuslate and int 0/0 setup with subinterfaces. You can have multple ip's assigned to 0/0 by typeing int 0/0.1, int 0/0.2 etc. What they call a router on a stick. Each of those will be setup for the corrosponding vlans. That's where the magic happens. The router now has been trained to associate those ip's to vlans. The next step is to setup the routers dhcp pool for those networks. VOIP is setup similar but using the telephony-service. I could give examples, but it would make this post very long and tedious. I highly suggest looking up vids on youtube and joining channels. Danscourses, CBTnuggets, Stormwind. There is some good stuff out there. Plan your topology with packet tracer etc. Good Luck!

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