Talk:Virtual LAN

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    • Define PVID (Port VLAN ID) [1]

    VLAN 1[edit]

    Virtual Local Area Networks often referred to as VLANS are basically configured to separate the broadcast domain in a switch. Now suppose there is a switch which has 100 ports out of which 40 belong to the marketing department of a company and rest 60 belong to sales. Now if marketing department never use data broadcasted by the sales department, then there is no use sending this data to them whenever a computer in the sales departement broadcasts a piece of information and actually there is a disadvantage in doing so, it just encourages congestion in the network. So to solve this problem, the concept of VLANs was introduced. What Vlan will do is, it will divide a switch into two different broadcast domains, so even if somebody in sales does a broadcast, the particular data wont go to people in marketing, which is quite advantageous.

    But its important to remember that by default all the ports in a new switch belong to Vlan 1, and this Vlan 1 can never be deleted or edited, but we can make more vlans and assign each port to a particular Vlan.This way the broadcast domain can be changed.

    What is this "VLAN 1" (mentioned above and in a free-floating sentence on the main page). Nowhere has the concept of naming VLANs been introduced or any explanation of how they are named or numbered. It sounds to me like "VLAN 1" might be part of a particular scheme of VLANs, and so this information has little to do with VLANs in general. Is it a tip to do with a particular manufacturer's VLAN system? As a newcomer trying to read the main article this information seems out of place and irrelevant. Chard 17:49, 21 February 2007 (UTC)

    I agree, and removed the following statement:

    VLAN 1 is the default VLAN; it can never be deleted. All untagged traffic falls into this VLAN by default.

    Whether VLAN 1 is default or can be deleted is up to the switch manufacturer. Untagged traffic uses whatever VLAN is defined as "native" when using 801.2q or when the port is on only one VLAN. --Rick Sidwell 01:18, 24 February 2007 (UTC)

    taking vlan trunks into a host[edit]

    is it possible if say a server is short on network cards to take a vlan trunk into the server and de-mulitplex it in software rather than connecting the server to a port on every vlan? Plugwash 04:53, 7 November 2005 (UTC)

    Yes, if the server supports 802.1q. Keep in mind that "trunk" is not a standard term (although commonly used by Cisco and others), so look for 802.1q or vlan tags, not trunks in the server documentation. Some products use "trunk" to mean something entirely different, so this can get confusing.
    this is certainly possible; on Linux you need a small program to configure the driver, though not all cards are physically able to do 802.1q IIRC. On Windoz it is similar - the network interface manufacturer will usually supply a utility to configure the driver. 10:57, 13 November 2005 (UTC)
    I just want to mention this article does a good job on describing what need to be done to make host vlan aware [2]

    link to vlan faq just advertisment[edit]

    Isnt the link to the FAQ just advertisment for ZeroShell? 22:23, 23 February 2007 (UTC)


    Single wire = hub not switch[edit]

    "A VLAN consists of a network of computers that behave as if connected to the same wire"

    Doesn't this incorrectly imply a VLAN is a single collision domain?

    I suppose that could be a source of confusion- I've changed the language in question. --Clay Collier 02:19, 14 June 2007 (UTC)

    Switches Have No Collision Domain?[edit]

    I don't think the following statement is correct:
    Section: Protocols and design

    " When Ethernet switches made this a non-issue (because they have no collision domain) ... "

    Switches do have a collision domain. Right?
    -Manavkataria 14:40, 30 August 2007 (UTC)

    No collision domain, but do have broadcast domain. (talk) 01:00, 22 February 2008 (UTC)
    They do have collision domains, one on each port. Pgallert (talk) 16:25, 29 April 2008 (UTC)
    if the links are all full duplex (which most if not all switches support) then there are no collision domains. 02:17, 30 April 2008 (UTC)
    Yes, there are. As Pgallert said, there's one per port. If two hosts simultaneously send a packet to a third there is a collision at the port servicing this third host. (talk) 23:02, 3 December 2009 (UTC)
    No, post on 30 April 2008 is correct. If two hosts simultaneously send a packet to a third, there is no collision, the packets are queued up. That is the fundamental difference between switches and hubs. (talk) 22:16, 22 May 2012 (UTC)
    This is not the difference between switches and hubs. Hubs are dumb devices, in that there is no logic behind the way it forward L2 franes; its basically just an electrical device. It receives a frame on one port and floods the frame out all other ports. Hubs are not capable of full duplex line speeds, meaning it cannot send and receive at the same time. The Carrier sense multiple access with collision detection algorithim was designed to detect collisions and proceed in the event of a collision. Switches do have collision domains, they just are far less likely to occur because of full duplex line speeds and the basic logic by which switches operate. They perform a lookup against a MAC address table, and only forward the frame out the link for which it has a MAC address entry. If no entry exists, it floods the frame the same way a hub would. MAC entries are added when the switch receives a frame with a source MAC it doesn't have an entry for. Getting back to collision domains though, they can't, or shouldn't occur when only 1 device is connected per port, but can occur over links with more than one host attached (like between switches) and even this is only possible if the link is functioning at half-duplex for some reason instead of full-duplex. ...nubs ;-) (talk) 06:22, 8 November 2016 (UTC)
    You might want to read up on how a switch works. The essential difference is that a repeater cannot buffer anything while a switch can buffer (so many) frames and queue them on the outbound ports. With a switch and all ports in half-duplex, there's a collision domain on each port, ie. if there is a collision while the switch tries to send, the switch will retry the packet and not the initial sender as with a hub. --Zac67 (talk) 07:38, 8 November 2016 (UTC)

    Unwieldy sentence[edit]

    This sentence needs editing: "Both ISL and IEEE 802.1Q tagging perform explicit tagging as the frame is tagged with VLAN information explicitly." - Dougher (talk) 05:39, 23 July 2008 (UTC)

    So does this one: "By definition, switches may not bridge IP traffic between VLANs as it would violate the integrity of the VLAN broadcast domain." What is meant by the word "it"? If "it" means "doing so" then that's what it ought to say. (talk) 23:07, 3 December 2009 (UTC)
    The first sentence you could possibly replace "tagging" with "protocols" and replace "VLAN information..." with "VLAN ID's", ending the sentence there; They have already mentioned that frames are explicitly tagged earlier.

    The second sentence I don't have a problem with as I think its more an issue of preference or style than clarity or grammatical acuity; 'It' refers to 'bridging IP traffic'. (talk) 06:40, 8 November 2016 (UTC)

    Article title: "VLAN" or "Virtual LAN"[edit]

    VLANs are much more commonly called VLANs than Virtual LANs, so I'm surprised that VLAN redirects to Virtual LAN. I think that the non-redirected article title should be VLAN, and Virtual LAN (and Virtual Local Area Network) should redirect to VLAN. Pelago (talk) 11:02, 27 November 2008 (UTC)

    I concur; in most documentation I've seen, the term is usually "VLAN". But then we're almost always talking about 802.11q; does anyone who still deals with older equipment have any guidance on the naming?
    Having said that, the way this article is structured, 802.11q is really the only thing being talked about, and furthermore the "concept" of VLAN is being conflated with "tag numbering".
    We need to make much clearer the distinction between "VLAN" (an ethernet broadcast domain) and "VLID" (the numbers used for tagging packets on a particular link between routers), since the latter can vary within a VLAN when more than 2 routers are involved.
    12:45, 31 December 2012 (UTC) — Preceding unsigned comment added by Martin Kealey (talkcontribs)
    To achieve accessibility by novices, we try to avoid acronyms in titles. That has to be balanced against the situation where some concepts are known almost exclusively by their acronyms and nobody knows what they stand for. I think the current title strikes a good balance. ~KvnG 14:43, 9 August 2014 (UTC)
    There has been this dilution of what VLANs implied as a layer 2 concept, and what 'tagged' VLANs as a layer 3 concept are good for. There were fundamental security features at layer 2 that cannot (IMO) be implemented as effectively at layer 3 (in software). You could run 2 subnets that were essentially completely isolated from one another at L2. I have L3 switches and full blown routers and right now I'm about ready to replace my L3 switches and go back to L2. I think its an important distinction and you risk losing that knowledge when you blur the lines between the two. Frankly, if the two had been introduced to me as two separate concepts from the very beginning, it probably would have saved me tons of frustration along the way. Its important to understand the fundamental differences between layers in the OSI model. It may seem minor, but you won't get anywhere if you're building on a poor foundation. (talk) 07:08, 8 November 2016 (UTC)

    Is ISL supported by CISCO?[edit]

    In the article a sentence saying that ISL is no longer supported by cisco has a line through it. Could somebody check to see if it is true, and either remove the sentence entirely or remove that formatting based on whether or not it is? (talk) 20:40, 4 August 2009 (UTC)

    History of VLANs[edit]

    After reading the history section and reading things that were rather absurd, I downloaded and read the referenced articles. Whoever wrote the history section clearly read those articles, but did not understand them. Almost every sentence in the section gets fundamental things wrong; e.g. a voice network does not require a terabit of bandwidth to be successful, merely that was the estimated bandwidth of the U.S. telephone network in its entirety at the time. It reminds me of a well written troll, a segment of the British sitcom "The IT Crowd", or gibberish you get after a game of telephone. The references are valuable, but the entire section needs to be rewritten from scratch. Obscuranym (talk) 04:38, 22 October 2010 (UTC)

    If you think you have a better understanding of the topic, please don't just scold the rest of us about how it should be done. Instead, be bold and fix it yourself, in the manner you think needs to be done. DMahalko (talk) 22:06, 22 October 2010 (UTC)

    VLAN is not only IEEE 802.1Q[edit]

    This article is Virtual LAN, not Ethernet VLAN nor IEEE 802.1Q. Even if the latter is the predominant technology today.

    I think it could be interesting to add more emphasis on legacy or alternate technologies. For historical considerations as well as for easier understanding of the concept.

    As an example, in the book Virtual LANs (ISBN 047-1177326) p.234, there's a reference to an earlier (?) technology called Intelligent Wiring Hub. According to the book, it is based on time division multiplexing to partition the backplane channel. Resulting on temporal multiplexing of several logical LAN on the same physical LAN. By googling a little, I found some references to this technology to share a backbone bandwidth between several LAN protocols (namely Ethernet and TokenRing). See the press article Wiring hub ties Ethernet, TokenRing over FDDI.

    - Sylvain Leroux (talk) 10:56, 30 November 2010 (UTC)

    "using them for the original purpose would be rather unusual"[edit]

    What does it mean under history where it says "using them for the original purpose would be rather unusual"? Is the original, deprecated purpose combining multiple ethernets together, or eliminating bottlenecks? It's not clear. Family Guy Guy (talk) 02:48, 20 August 2011 (UTC)

    Virtual network merge[edit]

    I'm not convinced that Virtual network is related to VLAN. I've started a discussion. Let's get this resolved before attempting a merge. --Kvng (talk) 18:19, 6 November 2011 (UTC)

    I'd suggest they are not the same and should not be merged. Specifically, a VLAN is configured on a physical switch to segregate broadcast domains. A virtual network is configured within a virtual environment. For example, I can run multiple virtual machines on a single server and use a virtual network to connect them. I can then choose to connect the virtual network to the host computer, to the outside network that the host computer is connected to, or leave the virtual network isolated from the host and the physical network. - DRG 28 Feb 2012

    no merge - VLAN is a network virtualization technique, but it's not (commonly) the same as a virtual network. Virtual network (virtual switch): Layers 1&2, VLAN: Layer 2, VPN: Layer 3. Zac67 (talk) 14:28, 17 May 2012 (UTC)
    I removed the merge banners. --Kvng (talk) 01:22, 20 May 2012 (UTC)

    Intro missing the point?[edit]

    After reading and rereading the first paragraph I'm afraid that it misses the point. VLAN isn't about joining parts together to a larger broadcast domain - that you can easily do by chaining switches -, it's rather about partitioning a physical network infrastructure into virtual separated domains. In terms of network virtualization, you're building virtual (layer 2) networks on top of an existing network. Additionally, joining hosts together to a broadcast domain regardless of physical location sounds more like a bridiging job (possibly with tunnelling/VPN) and isn't really about VLAN. Is it? Zac67 (talk) 21:17, 5 June 2012 (UTC)

    I don't think there's anything technically wrong with what exists in the lead but I think it does need to mention partitioning and VLAN tagging. --Kvng (talk) 13:50, 7 June 2012 (UTC)
    Nothing technically wrong but obscuring the main point (see "VLAN vs. WAN" below). I've tried a more straightforward approach while conserving as much possible of the previous version. Zac67 (talk) 16:44, 23 July 2012 (UTC)

    VLAN vs. WAN[edit]

    Would it be a lot of a hassle to make a section contrasting a VLAN from a WAN explaining why they differ from each other? — Preceding unsigned comment added by (talk) 13:20, 22 July 2012 (UTC)

    I've reworked the lead paragraph more to the point, hope everything becomes clearer now: VLAN is a technique of partitioning a local network while WAN is a general term for an extremely large network. Zac67 (talk) 16:44, 23 July 2012 (UTC)

    Number of VLANs.[edit]

    As we know that a single port can support 2 vlans one for data and for voice. though how and why does a switch support so many or thousands of vlans? — Preceding unsigned comment added by (talk) 10:19, 10 April 2013 (UTC)

    A single physical port can support up to 4095 VLANs (coventional) or even up to 16.8 million with IEEE 802.1aq (Shortest Path Bridging). Zac67 (talk) 17:59, 10 April 2013 (UTC)

    About talk membership.[edit]

    I tried to insert it in the article but was too bad formatted (i wrote it in open office). So, since i'm against losing contributions (not really lost since there is the history) at least i try to put the contribution in the nearest page to the article, its talk page. Moreover i believe that when there is a contribution, even "not acceptable" the community is more willing to take actions, instead when there is nothing, well nothing happens. So here it is, i have to use the "pre" tag to format it quickly.

    How to decode a VLAN definition with small examples.
    Using the information from the 3com manual (1) we can say that:
      1. A not member port is not belonging to the VLAN, so packets that are
      coming in those ports are not considerered, and no packets of the
      VLAN are sent out from those ports.
      For example the port 5 is not member of the VLAN "Gäste", so the
      packets incoming from that port are not considered and no packet is
      sent from that port (unless special rules applies but we don't use
      them, normally).
      2. An untagged port can exist in only one VLAN. That is, the port 6 is
      untagged in the VLAN "VoIP" and cannot be present as untagged in the
      other VLANs (can be present in other VLANs only as tagged, see
      later). Packet that are coming in the untagged port are modified as
        2.1 If the packet has no VLAN id, then is tagged with the VLAN id of
        the VLAN to which the port belongs.
        For example if an untagged packet goes in to the port 6 and the
        port 6 is belonging to: VID 2 as untagged port, VID 3 as tagged
        port, VID 4 as tagged port; then the packet will be assigned to
        the VLAN that contains the port 6 as untagged, thus it will get
        the VID 2.
        2.2 If a packet has a VID set then it is accepted only if the VID
        match with the VID of the VLAN that contains the untagged port,
        else is discarded (unless the port is present in other VLAN as
        tagged, see later).
        For Example a packet with VID 1 goes in the port 6 that is
        belonging to the VLAN with VID 2 as untagged, it is discarded,
        while a packet with VID 2 is accepted.
      Packets that are coming out of the untagged port will be modified as
        2.3 If the untagged port belongs to the default VLAN and the packet
        VID is the same of the default VLAN VID, then unset the packet
        VID and send the packet out.
        Otherwise if the untagged port belongs to a VLAN that is not a
        default one, send the packet without changing its VID value.
        (the rule No.1 will avoid to send packets from ports that
        doesn't belong to the VLAN of the packet).
        For example if the default VLAN has id 5, and the port 34 is
        beloning to the default VLAN as untagged, a packet with VID 5
        will be sent from this port with the VID value cleared.
        Instead if the port 34 is beloning to the VLAN "Gäste", with VID
        3, as untagged, a packet with VID 3 will be sent from this port
        with the VID value unchanged.
      3. A port that is tagged can be tagged in several VLANs, plus it can be
      present as untagged in one further VLAN. Packets that are coming in
      the tagged port are handled as follows:
        3.1 If the packet has the same VID of the VLAN that contains the
        port, it will be accepted, else will be discared. If no VID is
        set, either the rules for untagged port applied when the port is
        present as untagged in one VLAN, or the packet is discarded.
        For example if the port 3 is present as tagged in the VLANs with
        VIDs 3, 4, 5. Then a packet with VID 3 will be accepted and
        routed in the VLAN with VID 3, a packet with VID 4 will be
        accepted and routed in the VLAN with VID 4 and so on. A packet
        with VID 2 will be discarded.
      Packets that are coming out from the port are handled as follows:
        3.2 The packet will have the VID set to the value of the VLAN.VID
        that is handling it.
        For example a packet of the VLAN with VID 3 is going out from
        the tagged port, it will have the VID set to 3.
    (1)3Com Switch 4210G Family , Configuration Guide. Page 6-6

    -- (talk) 08:27, 5 August 2014 (UTC)

    "physical object recreated in software"[edit]

    @FT2: While I appreciate your recent edits, the "software" part is problematic. It suggests that VLANs are realized in software which isn't the case. Any objections changing that to something in the line of "(additional) logic"? --Zac67 (talk) 16:53, 30 April 2017 (UTC)

    I think there's room for improvement in those contributions. Please make some WP:BOLD changes and we'll see how it looks. ~Kvng (talk) 13:49, 3 May 2017 (UTC)
    Thanks for the feedback – I went ahead and made a few other fixes and updates on the way. --Zac67 (talk) 18:19, 4 May 2017 (UTC)