turn part of the cisco switch into a plain switch

Discussion in 'Cisco' started by a, Feb 13, 2007.

  1. a

    a Guest


    I would like to turn a few switchports of my 3560 into a completely separate
    dummy plain switch. Is it possible?
    I have configured a few ports to be no access vlan. Devices connected in
    these ports are able to ping each other.
    However, devices connected in these ports are not able to ping the devices
    connected in ports that have assigned vlans. This makes the switch
    configuration not equivalent to a separate dummy plain switch. How to make
    the separation possible?

    a, Feb 13, 2007
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  2. a

    BernieM Guest

    Ports configured as access ports default to vlan 1 unless they have been
    assigned to another vlan. Configuring "no switchport access vlan" puts then
    into the default vlan ... vlan 1. Hosts connected to those ports can ping
    each other because they are in the same vlan and cannot ping hosts in other
    vlans ... as you would expect from a 'dummy plain sitch'.

    What switching rules do you expect?

    BernieM, Feb 13, 2007
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  3. a

    a Guest

    Hi Bernie
    Thanks for your reply.
    But I have used no access vlan 1 for that switchport, is it still in vlan 1?
    If the devices are in VLAN, then it is not a dummy switch.
    It is because the packet will first try to find its default VLAN interface.
    A dummy switch is just like a physical layer switch with CLI control. Just a
    little bit more than a piece of cable.
    Is it possible?
    a, Feb 13, 2007
  4. a

    JF Mezei Guest

    You want say 4 ports to act as if they were on their own independant dummy
    switch, right ?

    Then you put those 4 ports into their own vlan (say vlan 7). Then any/all
    traffic that is sent into any of those 4 ports will only ever go to those 4
    ports, just like it was in its own switch.

    Broadcasts sent by a device connected to one of those 4 ports will only go
    to the other 3 ports on that VLAN.
    The would be a hub then.

    A hub transmits all information from all ports to all ports.
    A switch learns the ethernet addresses of devices connected to each port,
    so a unicast to a known ethernet address gets sent to only that port.

    I am not certain you could turn all 4 ports into a "hub". But you can make
    one port listen in on the remaining 3 with port mirroring. This way, one
    port would see all the traffic sent/received by the other 3 ports. (acting
    a bit like a hub).
    JF Mezei, Feb 13, 2007
  5. a

    BernieM Guest

    You may have used "no access vlan 1" but does that appear in the config? A
    switchport by default is in vlan 1 but "switchport access vlan 1" is one of
    those default settings that doesn't appear when you do a "show run".

    What do you mean by a dummy switch. By default all ports on a switch are in
    the same vlan but not 'on the same piece of wire'. As JF Mezei explained
    that's the difference between a switch and a hub. For the switch to act
    like a hub you'd have to disable the 'mac-address table' function so all
    packets get transmitted out all ports. Is this what you're expecting?

    What do you mean by "the packet will first try to find its default VLAN
    interface"? Frames coming from the servers and frames coming from the
    switch, on an access port, are not vlan tagged.

    BernieM, Feb 13, 2007
  6. a


    Dec 23, 2012
    Likes Received:
    If you dont what to ping each other or specific ping is required, use PVLAN concept. ISP does use this concept in there domain.
    mprasad079, Dec 23, 2012
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