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802.1q tag-based vs port-based VLANs

Discussion in 'Wireless' started by tripwire45, Dec 21, 2003.

  1. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    I understand the basic concept of a switch placing a unique VLAN ID or tag in an Ethernet frame to identify the frame as it's forwarded across the switch fabric, but what is the difference between tag-based and port-based VLANs. It seems that in both, specific ports are configured to a specific VLAN membership ID and that this information must be contained in frames originating from within the membership. Thanks.

    EDIT: Actually, let's add MAC address-based VLANs, IP address-based VLANs and Protocol-based VLANs to the mix, just to keep it interesting.

    EDIT again (hours have passed), I've moved into the realm of trying to see if "IP address-based VLANs" are a different breed of cat than "Protocol-based VLANs". I'd think if a Layer 3 aware switch was identifying VLAN traffic based on Network Layer addressing, there wouldn't need to be separate catgories of info for IP vs IPX and Appletalk and what have you. When we say "protocol" could we be talking about VLAN identification based on Layer 7 protocols perhaps? Having trouble getting Google to supply consistant info. Thanks.
     
    Certifications: A+ and Network+
  2. Phil
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    Phil Gigabyte Poster

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    Ok Trip, you appear to be having a whole technical discussion with yourself here :D What is your question at the moment ? I found this in a quick google, don't know if it'll be any use.
     
    Certifications: MCSE:M & S MCSA:M CCNA CNA
    WIP: 2003 Upgrade, CCNA Upgrade
  3. tripwire45
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    tripwire45 Zettabyte Poster

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    Thanks, Phil. I found the analogus link for the US site for this product. What I'm looking into, and maybe I'm "barking up the wrong tree" so to speak, is four catagories of VLAN membership:

    tag based VLANs
    port based VLANs
    IP address based VLANs
    Protcol based VLANs

    As far as I can tell so far, IP address based VLANs are just a subset of Protocol based VLANs. I was wondering if maybe I'm missing something since "protocol" can mean more than just "routed protocol" (layer 3). Do some switches based VLANs on other than layer 3 protocols? Haven't found much of anything to base it on so I'm inclined to say "no" but then why is the list broken down the way it is in my (sorry but it's confidential) source?
     
    Certifications: A+ and Network+
  4. Phil
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    Phil Gigabyte Poster

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    The way I've understood things, and I'm prepared to be shot down in flames here :) The tag is just a method for switches to identify which vlan a packet belongs to, the other method being by mac address. Port / mac /protocol based vlans are the methods by which the vlans are assigned. I don't think there is a port based vlan or tag based vlan, rather that the port based vlan uses a tag to identify the vlan a packet comes from. As for the protocol issue the link I gave earlier has this quote

    Is the non-routable protocols bit what you were talking about ? I don't think that point is particularly clear but what it seems to be saying is that you can also use protocol based vlans to assign vlans to non-routable protocols.
     
    Certifications: MCSE:M & S MCSA:M CCNA CNA
    WIP: 2003 Upgrade, CCNA Upgrade
  5. tripwire45
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    tripwire45 Zettabyte Poster

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    That's probably it, Phil. Naturally, the protocols don't have to be routable since switches don't route (so called "layer 3 switches" aside). Unless something else comes up, guess that's the approach I'll take. I'd already taken MAC based VLANs into account and just forgot to mention that one in my list.

    It's interesting because Cisco doesn't have a lot on this on their site. The CCNA coursework only really covers tag based VLANs. I'm finding paragraphs here and there on the web, but nothing really "meaty" in terms of content on the protocol based issue. Thanks for diving in on this one, Phil.
     
    Certifications: A+ and Network+
  6. AJ

    AJ Administrator Administrator

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    Now I could be barking up the wrong tree here but we use VLANS at the school I work at. All of the boarding houses, depts, admin and separate building are all on different subnets (192.168.x.x). These are all given a different VLAN ID no on the main routing switch. This is so that the little darlings can't flood the network with peer to peer games from boarding house to boarding house. These I believe are untagged VLANS with unmanaged switches in the houses.

    Now the Admin Dept want to be completely separate from the main school network and are in fact still an NT 4 Domain with W9x clients whilst the main school is fully W2K. The Admin Dept is spread throughout the school and they need to access their network. At present we use 3COM managed switches which allow us to assign one of the ports to a specific VLAN. This is tagged. This means that the machine that is plugged into the particular port on the switch can only get to the network (VLAN) the has been assigned to that port. All of the other ports can access the schools network as usual. So you can run 2 or more networks through a managed VLAN switch.

    Hey I think that's how it goes.

    AJ
     
    Certifications: MCSE, MCSA (messaging), ITIL Foundation v3
    WIP: Looking at doing ..................
  7. tripwire45
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    tripwire45 Zettabyte Poster

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    I think I found out why IP based vlans and protocol based vlans are in separate catagories. Check out this article from Network World and scroll down and read the piece about "Using VLAN to manage legacy protocols". Thanks for the feedback, everyone.
     
    Certifications: A+ and Network+

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