QinQ Header size

Discussion in 'Cisco' started by flamer die.spam@hotmail.com, May 18, 2011.

  1. flamer

    flamer Guest

    When using an 802.1qtunnel does the number of CE-VLAN's pushed across
    the tunnel increase the frame size, or can i push as many inner vlan
    tags through without increasing the header size?

    Form our testing every extra CE vlan added to a tunnel requires an
    extra 4 bytes added to the MTU to allow the traffic to flow.
     
    flamer , May 18, 2011
    #1
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  2. On 19/5/11 12:51 AM, flamer wrote:
    > When using an 802.1qtunnel does the number of CE-VLAN's pushed across
    > the tunnel increase the frame size, or can i push as many inner vlan
    > tags through without increasing the header size?
    >
    > Form our testing every extra CE vlan added to a tunnel requires an
    > extra 4 bytes added to the MTU to allow the traffic to flow.


    Every tunnel adds 4 bytes to Ethernet frame.

    BR,
    A.C.
     
    Anonymous coward, May 19, 2011
    #2
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  3. flamer

    flamer Guest

    On May 19, 8:25 pm, Anonymous coward <>
    wrote:
    > On 19/5/11 12:51 AM, flamer wrote:
    >
    > > When using an 802.1qtunnel does the number of CE-VLAN's pushed across
    > > the tunnel increase the frame size, or can i push as many inner vlan
    > > tags through without increasing the header size?

    >
    > > Form our testing every extra CE vlan added to a tunnel requires an
    > > extra 4 bytes added to the MTU to allow the traffic to flow.

    >
    > Every tunnel adds 4 bytes to Ethernet frame.
    >
    > BR,
    > A.C.


    Do you mean every VLAN adds 4 bytes to the frame?
     
    flamer , May 20, 2011
    #3
  4. On 20/5/11 3:06 AM, flamer wrote:
    > On May 19, 8:25 pm, Anonymous coward<>
    > wrote:
    >> On 19/5/11 12:51 AM, flamer wrote:
    >>
    >>> When using an 802.1qtunnel does the number of CE-VLAN's pushed across
    >>> the tunnel increase the frame size, or can i push as many inner vlan
    >>> tags through without increasing the header size?

    >>
    >>> Form our testing every extra CE vlan added to a tunnel requires an
    >>> extra 4 bytes added to the MTU to allow the traffic to flow.

    >>
    >> Every tunnel adds 4 bytes to Ethernet frame.
    >>
    >> BR,
    >> A.C.

    >
    > Do you mean every VLAN adds 4 bytes to the frame?


    No, every tunnel adds 4 bytes to the frame.
     
    Anonymous coward, May 20, 2011
    #4
  5. flamer

    Stephen Guest

    On Thu, 19 May 2011 18:06:09 -0700 (PDT), "flamer
    " <> wrote:

    >On May 19, 8:25 pm, Anonymous coward <>
    >wrote:
    >> On 19/5/11 12:51 AM, flamer wrote:
    >>
    >> > When using an 802.1qtunnel does the number of CE-VLAN's pushed across
    >> > the tunnel increase the frame size, or can i push as many inner vlan
    >> > tags through without increasing the header size?

    >>
    >> > Form our testing every extra CE vlan added to a tunnel requires an
    >> > extra 4 bytes added to the MTU to allow the traffic to flow.

    >>
    >> Every tunnel adds 4 bytes to Ethernet frame.
    >>
    >> BR,
    >> A.C.

    >
    >Do you mean every VLAN adds 4 bytes to the frame?


    Nope

    assuming you use 802.1Q format packets (there is a cisco specific vlan
    flavour which is more complicated and that adds more overhead).

    when you use 1 "layer" of vlan tags, you have 12 bits of vlan numbers
    you can use - you get approx 4000 vlans to work with, although some
    cisco setups will limit you to around 1000.

    you can use more than 1 "layer" of vlans on a single packet.

    eg if you take a carrier ethernet service, you might get a WAN
    ethernet interface with several vlans, each of which acts as a link to
    a different remote site, and inside that tunnel you can use your own
    vlans.

    So 1 vlan tag on the packet used to tell the service provider where to
    send the packet, 1 customer vlan tag within that to select your target
    vlan, and inside that the meat of a normal Ethernet packet.

    Total of 2 vlan tags per packet, 4 bytes overhead for each.

    If you are getting more overhead than that something is set up wrong.

    i suggest you get hold of a packet sniffer and see what is actually
    going out in the packets

    Good luck
    --
    Regards

    - replace xyz with ntl
     
    Stephen, May 20, 2011
    #5
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