3750 VLANs

Discussion in 'Cisco' started by Bob Simon, Oct 31, 2007.

  1. Bob Simon

    Bob Simon Guest

    Can the Ethernet ports of a 3750 be members of two different VLANs?
    If so, how is this configured?
    Bob Simon, Oct 31, 2007
    #1
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  2. Bob Simon

    Trendkill Guest

    On Oct 31, 7:46 am, Bob Simon <> wrote:
    > Can the Ethernet ports of a 3750 be members of two different VLANs?
    > If so, how is this configured?


    Yes and No. You can have auxiliary VLANs configured...most often used
    for voip devices. What this means is, the device directly plugged
    into the port is on the primary vlan (say the voice vlan if this is a
    phone), and then whatever device is plugged into the back of the cisco
    phone is put onto the secondary/auxiliary vlan to keep voice/data
    separate.

    If you are asking about a port truly being in two different vlans,
    that is not possible without trunking (generally ISL since dot1q is
    proprietary to cisco). If you trunk, you can trunk both vlans and the
    box will need to have logical interfaces in both (unless this is
    promiscuous and for a sniffer or probe, then it can just listen).
    Trendkill, Oct 31, 2007
    #2
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  3. Trendkill <> writes:
    >On Oct 31, 7:46 am, Bob Simon <> wrote:
    >> Can the Ethernet ports of a 3750 be members of two different VLANs?
    >> If so, how is this configured?


    >Yes and No. You can have auxiliary VLANs configured...most often used
    >for voip devices. What this means is, the device directly plugged
    >into the port is on the primary vlan (say the voice vlan if this is a
    >phone), and then whatever device is plugged into the back of the cisco
    >phone is put onto the secondary/auxiliary vlan to keep voice/data
    >separate.


    FWIW: this is done using a form of Cisco trunking..

    >If you are asking about a port truly being in two different vlans,
    >that is not possible without trunking (generally ISL since dot1q is
    >proprietary to cisco). If you trunk, you can trunk both vlans and the
    >box will need to have logical interfaces in both (unless this is
    >promiscuous and for a sniffer or probe, then it can just listen).



    Unlike the ancient Cisco switches, multi-vlan was dropped in all
    modern line of switches. Probably for good measure.

    In reflection, there's not really a good reason to have ports in
    multi-vlan use, its not a good security model.
    Doug McIntyre, Oct 31, 2007
    #3
  4. Bob Simon

    Thrill5 Guest

    ISL trunking is Cisco proprietary, dot1q is a standard. Only Cisco's really
    old switches only support ISL, and all the recent ones only support dot1q.


    "Trendkill" <> wrote in message
    news:...
    > On Oct 31, 7:46 am, Bob Simon <> wrote:
    >> Can the Ethernet ports of a 3750 be members of two different VLANs?
    >> If so, how is this configured?

    >
    > Yes and No. You can have auxiliary VLANs configured...most often used
    > for voip devices. What this means is, the device directly plugged
    > into the port is on the primary vlan (say the voice vlan if this is a
    > phone), and then whatever device is plugged into the back of the cisco
    > phone is put onto the secondary/auxiliary vlan to keep voice/data
    > separate.
    >
    > If you are asking about a port truly being in two different vlans,
    > that is not possible without trunking (generally ISL since dot1q is
    > proprietary to cisco). If you trunk, you can trunk both vlans and the
    > box will need to have logical interfaces in both (unless this is
    > promiscuous and for a sniffer or probe, then it can just listen).
    >
    Thrill5, Nov 1, 2007
    #4
  5. Bob Simon

    Trendkill Guest

    On Oct 31, 10:43 pm, "Thrill5" <> wrote:
    > ISL trunking is Cisco proprietary, dot1q is a standard. Only Cisco's really
    > old switches only support ISL, and all the recent ones only support dot1q.
    >
    > "Trendkill" <> wrote in message
    >
    > news:...
    >
    > > On Oct 31, 7:46 am, Bob Simon <> wrote:
    > >> Can the Ethernet ports of a 3750 be members of two different VLANs?
    > >> If so, how is this configured?

    >
    > > Yes and No. You can have auxiliary VLANs configured...most often used
    > > for voip devices. What this means is, the device directly plugged
    > > into the port is on the primary vlan (say the voice vlan if this is a
    > > phone), and then whatever device is plugged into the back of the cisco
    > > phone is put onto the secondary/auxiliary vlan to keep voice/data
    > > separate.

    >
    > > If you are asking about a port truly being in two different vlans,
    > > that is not possible without trunking (generally ISL since dot1q is
    > > proprietary to cisco). If you trunk, you can trunk both vlans and the
    > > box will need to have logical interfaces in both (unless this is
    > > promiscuous and for a sniffer or probe, then it can just listen).


    Yes you are right...sorry...got mixed up for a second. Dot1q =
    standard, ISL = Cisco.
    Trendkill, Nov 1, 2007
    #5
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